Gluster linear scaling: How to choose wisely

We talk a lot about the linear scalability of Red Hat Gluster Storage, and we can generally back that up with empirical data. Indeed, homogeneously scaling out the storage nodes and network infrastructure can result in both capacity and throughput capabilities that are directly proportional. But it’s important to note that this is potential scalability, and how you use the volumes plays a vital role in the experience you have.

We architect optimal solution recommendations based on a few expectations:

  1. Most of the workload falls into a particular category—high throughput, small file, or latency sensitive, for example.
  2. When your capacity needs grow, so do your concurrent client demands.
  3. You’re using the glusterfs native client.

Let’s take a look at these points and how they affect your real scalability.

Architecting for workload

We know through thousands of test cycle results that there is a generally optimal server configuration that will apply broadly to a majority of workloads. This compiled knowledge is a huge benefit to you, the user, and it can greatly reduce your own time commitment in designing and testing fundamental system architectures. However, just up the stack from the server and network components are low-level configuration choices that you will make for every deployment. These choices are the big knobs—Particular to your workload there is likely one best choice for peak performance. And it’s important to note that these aren’t choices you can easily change later. Changes at these layers likely require moving data, potentially more than once, and data has inertia.

When you understand your majority workload, and preferably you isolate dislike workloads entirely, you will be positioned to make choices about server density (12, 24, or higher drive capacity), block-level configurations (e.g., HDD vs. SSD, RAID vs. JBOD, caching vs. not, block and stripe sizes), and Gluster volume geometry (e.g., replicated vs. dispersed, failure resiliency, arbiter bricks, tiering). Locked into these choices and the related workload, you’ll find it reasonably simple to integrate new nodes and bricks into the volume for predictable capacity and performance expansion.

Client concurrency

So you’ve built to your workload and everything is great. That is, unless your expectations aren’t aligned with a scale-out solution. Any single connection to the storage pool is bound by physics. One client communicates over one network link to one server to one file system and block stack. Sure, some design options allow for single-client concurrency to multiple stacks, but those come at a trade off, and each connection is still bound by physics and bottlenecked somewhere along the line. So if your need is to provide expanded throughput capabilities to a single or a small number of clients, you will likely find that horizontal scale-out won’t give you much performance benefit. There are some tricks we can use to architect for such a need, but it will never be an efficient solution.

To that end, an optimal design assumes you are operating at an appropriate client:server concurrency ratio. The best ratio will vary with your workload and the architecture decisions you make per the preceding discussion, but you can expect for most cases a ratio range of 12:1 to 48:1 to be appropriate for peak or plateau storage throughput capabilities. So if you build out a 12-node storage pool based on your capacity needs and then expect 4 client systems to use that storage concurrently, you’ll bottleneck on the server node I/O stack long before you saturate the aggregate system capabilities. But with an appropriate concurrent client count of say 150+ for your 12 server nodes, you may be operating at the peak capabilities of the system.

Client choice

Great! So you’re heeding all the advice here, and you’re going to deploy 12 Red Hat Gluster Storage nodes in an optimal architecture for 150 NFS clients. Well, hold on there a minute, buckaroo. We’re more than happy to support the NFS client, but you should know what you’re getting into.

When using the Gluster native client, data placement calculations are made on the client side. This means that each client is fully aware of the volume geometry and all server nodes participating, allowing it to determine how the data protection scheme is applied and which nodes and backend filesystems (bricks) each file will be written to. All client-to-server connections are then made efficiently based on this client-side intelligence. And because data placement among the distributed system is done pseudo-randomly, there is a statistically even distribution of work between the clients and servers and therefore predictable performance scalability.

When choosing NFS (or SMB), a client will make its connections to a single Gluster server. That server then has to apply the client-side intelligence for data resilience, conversion, and placement, and it will then make secondary network calls out to each participating server node for the file transaction. This inefficiency leads to a concurrency bottleneck far below the capabilities of the native client—You’ll still hit peak throughput at about the same client:server ratio, but that throughput will be well below what can be achieved on the same systems with the native client.

The one surprise that can come up with the NFS client is that if you do indeed require a lower client:server ratio, NFS can in some conditions outperform the native client at that concurrency level. YMMV on this, and you’ll still be far below the peak capabilities of the system, but it’s worth testing out if you’re absolutely determined to connect your 4 clients to your 12 Gluster nodes (but don’t say I didn’t warn you not to).

Oh yeah? Prove it.

Lucky for you, I did that already. Take a look at our published reference architectures and, in particular, our most recent Gluster Performance and Sizing Guide. And keep an eye out here for future publications as we continue to expand and refine our data.

Container-native storage for the OpenShift masses

By Daniel Messer, Red Hat Storage

 

Red Hat Container-Native Storage 3.6, released today, reaches a new level of storage capabilities on the OpenShift Container Platform. Container-native storage can now be used for all the key infrastructure pieces of OpenShift: the registry, logging, and metrics services. The latter two services come courtesy of the new block storage implementation. Object storage is now also available directly to developers in the form of the well-known S3 API. Administrators will enjoy a more robust cns-deploy utility, support for online volume expansion, and more choice in deployment topologies in the OpenShift Advanced Installer. Last, but just as important, it now supports more concurrent workloads serving over 1,000 persistent volumes with just 3 nodes.

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You know you must be doing something right when some of your users are looking to use your technology in different ways than expected. Initially, the idea of running GlusterFS alongside Kubernetes and OpenShift promised the ability to use a distributed storage system with a framework for distributed applications. They goes nicely together because both approaches are entirely based on scale-out software, hence independent of the underlying platform, and they are driven by a declarative API-driven design. On the GlusterFS side, that API is available in the form of an additional software daemon, called heketi. Things soon took a new direction when the first experiments of running the GlusterFS/heketi combination as an OpenShift workload were conducted.

A lot of engineering cycles later, the idea of hacking GlusterFS onto OpenShift has emerged to a fully supported product offering: container-native storage. Today, we are happy to announce container-native storage 3.6.

For the impatient: In essence, we have taken container-native storage from being an optional supplement in OpenShift to being a storage solution that now serves file, block, and object storage to applications on top of OpenShift and to the entire OpenShift internal infrastructure, as well.

For the curious reader, let’s go see how we did that….

Increase density

The first thing we had to do was ensure that container-native storage was a robust, scalable, long-term solution for the different possible OpenShift cluster sizes. When we launched container-native storage with OpenShift 3.2 last summer, the container images were based on Red Hat Gluster Storage 3.1.3 and, on average, each brick process on a GlusterFS host/pod consumed about 300 MB of RAM.

That may not sound like much, but you have to be aware that every PersistentVolume served by container-native storage results in a GlusterFS volume being created. Bricks are local directories on GlusterFS pods that make up volumes. The consistency of volumes across all its bricks (by default, 3 in container-native storage) is handled by the glusterfsd process, which is what consumes the memory.

In older releases of Red Hat Gluster Storage, there was one such process per brick on each host. It’s easy to see that with potentially hundreds of application pods in OpenShift requiring their own PersistentVolumes, the resulting number of brick processes in each GlusterFS pod will easily consume gigabytes of RAM and would create a significant effort to coordinate in each pod.

That many processes in a pod are an anti-pattern for Kubernetes and, even if we would have broken out those in separate containers, the memory overhead would still be huge.

Fortunately, Red Hat Gluster Storage 3.3 came to the rescue. Released just a little over 2 weeks ago, it introduced a new feature called brick-multiplexing. It’s easier to depict how this feature changes the structure of a GlusterFS pod in a diagram than a lengthy explanation:

With brick-multiplexing, only one glusterfsd process is governing the bricks such that the amount of memory consumption of GlusterFS pods is drastically reduced and the scalability is significantly improved.

By introducing brick-multiplexing in version 3.6, we are able to support over 1,000 PersistentVolumes in a single container-native storage cluster. The amount of memory consumed increases linearly, so that 32GB of RAM are only needed at the high end of that. The rule of thumb is roughly 30-35 MB RAM per volume on each of the participating GlusterFS pods.

Container-native storage can probably support an even greater number of volumes, and we hope to confirm that soon. Until then, you always have the option to either run more GlusterFS pods in your OpenShift cluster or deploy a second container-native storage cluster, governed by the same Heketi API service.

Optimized storage for logging/metrics

File storage is what containers on OpenShift (and in general) deal with today. It’s a ubiquitous, well-understood concept. There are also proposals for native access to block devices in pods, but they are still in design or planning phases.

That is—at least for now—storage (including block) in Kubernetes and OpenShift always ends up being a mounted file system on the host running the pod, which is then bind-mounted to the target container’s file system namespace. Block storage provisioners in OpenShift eventually format the device with XFS too, before handing it over to the container.

GlusterFS is a distributed, networked file system which, in contrast to local filesystems like XFS, allows shared access from multiple hosts and stores the data in the backend distributed across multiple nodes. This big advantage does not come without cost, however: Some type of operations that are fast and cheap on a local file system are quite expensive in a distributed file system.

For some workloads (e.g., OpenShift Logging and Metrics), this can be a show-stopper. To properly support those, we designed something that might seem counter-intuitive at first: gluster-block. Take a look at the implementation scheme below:

Yes, you see that right: We are using TCM (the Linux kernel’s iSCSI stack, also called LIO) managed by targetcli to create iSCSI LUNs from files on a GlusterFS volume and present those as block devices to pods. The TCM stack allows local storage of a Linux system to be made available on the network via the iSCSI protocol. In our specific case, the local storage is a large raw file on a GlusterFS volume. On the client side, the iSCSI block device will be formatted with XFS and then bind-mounted to the target container’s file system namespace.

But why go through all the trouble? In distributed file systems—and here GlusterFS is no exception—metadata-intensive operations like file create, file open, or extended attribute updates are particularly expensive and slow compared to a local file system. In particular, indexing solutions likes ElasticSearch (part of OpenShift Logging) and scale-out NoSQL databases like Cassandra (part of OpenShift Metrics) generate such workloads.  But also other database software might make heavy use of locking and byte-range locking, which are costly compared to simple read and writes.

In order to qualify OpenShift Metrics and Logging Services to run well on a container-native storage backend, a significant speed up was needed for a lot of special file system operations like these.

You can probably guess what we were thinking: In software, many problems can be solved by adding an additional layer of indirection.

The indirection in accessing data on GlusterFS via iSCSI instead of a normal GlusterFS mount converts otherwise expensive file system operations to a single stream of continuous reads and writes to a single raw file on GlusterFS. The TCM stack delivers this IO stream over the network via iSCSI. On the receiving end, the file in GlusterFS backing the iSCSI LUN is accessed via libgfapi, a userspace library to access files in GlusterFS without the need to mount a volume.

The clients, in our case containers in pods on OpenShift, still write to an XFS file system the iSCSI LUN is formatted with. As a result, simple client-level read and write requests remain virtually as fast as accessing the file directly on GlusterFS, but also all the other file system operations are converted into much faster reads and writes to the file backing the block volume because they are not distributed. From the perspective of GlusterFS, it’s a constant stream of basic read and write requests, which GlusterFS is efficient at. Of course, this comes with a trade-off: gluster-block is not shared storage.

Container-Native Storage version 3.6 now provides backend storage for OpenShift Logging and OpenShift Metrics with gluster-block. For the moment, the use of gluster-block in production is only supported for OpenShift Logging and Metrics services, but use of gluster-block beyond that is under qualification, and support is expected to be extended soon.

The Logging and Metrics services have strict performance and latency requirements and are important for any OpenShift cluster in production. They provide vital information and debugging capabilities for administrators. By design, they are scale-out services, because their storage backend (ElasticSearch for Logging, Cassandra for Metrics) supports a shared-nothing approach. However, in production you do not want additional shards of ElasticSearch and Cassandra run side-by-side with your application pods. That’s why there is a concept of infrastructure nodes in OpenShift that do not run business applications but are dedicated to OpenShift infrastructure components like these. Typically, these kind of servers only have storage locally available, which is limited in capacity and performance. Thus, it might quickly become insufficient to store the logs and metrics of hundred of pods. With container-native storage, you now have a scalable, robust, and long-term storage solution for logging and metrics that utilizes the entire cluster’s storage capacity.

Support a scale-out registry

There is one additional component in OpenShift that’s crucial for operations: the container image registry. This is where all the resulting images from source-to-image builds will be pushed to and where developers can upload their custom images. If it’s unavailable, those operations will fail, and users will be unable to launch new or update existing applications.

The default configuration for the OpenShift registry is to use `emptyDir` storage, that is, a local file system on the container host that depends on the registry pod’s lifetime. In this setup, the registry, of course, cannot be scaled out, updated, or restarted on another host.

Fortunately, as of version 3.5, container-native storage allows for a scale-out registry using shared storage on a PersistentVolume served by GlusterFS. This has several advantages:

  1. No external storage is required, like NFS, which can cause problems with metadata consistency with a busy registry.
  2. There is no dependency on provider storage (e.g., AWS S3 being unavailable in a VMware environment) for shared data access.
  3. The registry can now be scaled out, ideally across all infra nodes.
  4. The registry storage backend can grow dynamically with the platform.

The beauty of this is that it can be installed like this right away. Like we’ve already covered during the announcement of OpenShift Container Platform 3.6 earlier this year, the OpenShift Advanced Installer now supports deploying container-native storage and the registry on container-native storage out of the box. See this video here for details.

All you have to do since OpenShift Container Platform 3.6 is add a few lines to your Ansible inventory file.

To deploy an OpenShift registry backed by container-native storage, first add the following variable definition in the [OSEv3:vars] section:

openshift_hosted_registry_storage_kind=glusterfs

And then add a new host group defining the container-native storage nodes to the inventory, for example:

[glusterfs_registry]
infra-1.lab glusterfs_devices='[ "/dev/sdd" ]'
infra-2.lab glusterfs_devices='[ "/dev/sdd" ]'
infra-3.lab glusterfs_devices='[ "/dev/sdd" ]'

This is enough to tell the OpenShift Advanced Installer that it should create a basic 3-node container-native storage cluster, in this case on the infrastructure nodes, using the supplied devices to create bricks. From this cluster a PersistentVolume will be created and supplied to the registry DeploymentConfig.

That way the registry will be launched with shared storage, provided by container-native storage, and scaled to 3 instances across the infrastructure nodes. You get a highly available and robust registry out of the box with no additional configuration needed.

S3 object storage for applications

In addition to providing block and file storage services, Container-Native Storage 3.6 now provides an S3 object storage interface as a TechPreview. Application developers have a ready-to-use REST API at hand to provide object storage to workloads on OpenShift, just a HTTP PUT or GET request away.

Object storage in Red Hat Container-Native Storage 3.6 provides a simple yet scalable storage layer for distributed applications that were previously tied to specific cloud provider S3 object storage. These application now run with little or no modification on OpenShift.

In this implementation, a gluster-s3 service is deployed as a pod in your OpenShift cluster, and an OpenShift Route is generated for it. The Route’s URL is provided to applications as their S3 endpoint. The service receives the S3 requests and translates those to file system operations on GlusterFS volumes. The S3 buckets and objects are stored as directories and files on that volume, respectively.

For now, this service can be deployed with the cns-deploy utility. There are some new command switches available for this purpose:

cns-deploy topology.json --namespace gluster-storage --log-file=cns-deploy.log --object-account dmesser --object-user dmesser --object-password redhat

The new parameters allow you to specify a name for the S3 account (object-account, an aggregate of multiple S3 buckets, one per CNS cluster), a named user (object-user), and the authentication password for that user in that account (object-password). Once all of these 3 switches are presented, cns-deploy will create the glusterfs-s3 infrastructure.

Support for doing this with the OpenShift Advanced Installer is expected to follow soon. The design foresees exactly one S3 domain/account per CNS cluster, although multiple CNS clusters can be deployed easily.

Improvements for deployment and operations

Besides a whole bunch of new features, we’ve also introduced improvements in usability to make the container-native storage experience better.

In Container-Native Storage 3.6, the cns-deploy tool has been improved in a number of ways. It is now more idempotent, allowing the administrator to run the installer multiple times without having to start from scratch. There will still be error scenarios that may require manual intervention, but it should be much easier to recover from such errors. It will also deploy the required resources to use gluster-block and gluster-s3. Combined with the idempotency improvements, administrators will be able to run cns-deploy to deploy those features into an environment that’s already running container-native storage.

Container Native Storage 3.6 also provides improved integration with container-ready storage. All of our new features will work just as well on container-ready storage as container-native storage. In addition, we have introduced support for a configuration we’re calling Container-Ready Storage without Heketi. heketi is the volume management API service for GlusterFS. In this configuration, container-ready storage runs with the usual Red Hat Gluster Storage nodes outside the OpenShift cluster, but heketi resides as a pod within OpenShift. This has the advantage of making the heketi service highly available rather than residing on a single machine. For new deployments, the cns-deploy can be used to initialize a container-ready storage cluster in this configuration.

Another common scenario that is likely to occur over time, even with the short-lived nature of some workloads, is PersistentVolumes filling to capacity. This can happen when a user under-estimates the required capacity for a workload or the pod simply runs way longer than expected. In any case, heketi now allows for online volume expansion.

To take advantage of this, simply use the heketi-client on the CLI to expand the size of any given volume:

heketi-cli volume expand --volume=0e8a8adc936cd40c2df3698b2f06bba9 --expand-size=2

In the background, heketi changes the GlusterFS volume layout from a 3-way replicated to distributed-replicated. See below for a comparison from GlusterFS perspective.

Before volume expansion:

sh-4.2# gluster vol info vol_0e8a8adc936cd40c2df3698b2f06bba9

Volume Name: vol_0e8a8adc936cd40c2df3698b2f06bba9
Type: Replicate
Volume ID: 841bd097-659b-4b5d-b3ec-56bb8cc51c2f
Status: Started
Snapshot Count: 0
Number of Bricks: 1 x 3 = 3
Transport-type: tcp
Bricks:
Brick1: 10.20.5.232:/var/lib/heketi/mounts/vg_c05319c8a95eaa083adbedb7d43913fa/brick_4bf9ae183dacceccf4bf525186850bdd/brick
Brick2: 10.20.6.239:/var/lib/heketi/mounts/vg_bd7fbf9053d6340771f7b75ce2872339/brick_e1175aaaa8596aedc18bf8c56b42fe8d/brick
Brick3: 10.20.4.184:/var/lib/heketi/mounts/vg_0797a1d458309eec3e5e818a9b87f6c6/brick_2b5255cc2c0297e4e34eb6f1b4319fb9/brick
Options Reconfigured:
transport.address-family: inet
nfs.disable: on
cluster.brick-multiplex: on

After volume expansion:

sh-4.2# gluster vol info vol_0e8a8adc936cd40c2df3698b2f06bba9

Volume Name: vol_0e8a8adc936cd40c2df3698b2f06bba9 
Type: Distributed-Replicate 
Volume ID: 841bd097-659b-4b5d-b3ec-56bb8cc51c2f 
Status: Started 
Snapshot Count: 0 
Number of Bricks: 2 x 3 = 6 
Transport-type: tcp 
Bricks: 
Brick1: 10.20.5.232:/var/lib/heketi/mounts/vg_c05319c8a95eaa083adbedb7d43913fa/brick_4bf9ae183dacceccf4bf525186850bdd/brick 
Brick2: 10.20.6.239:/var/lib/heketi/mounts/vg_bd7fbf9053d6340771f7b75ce2872339/brick_e1175aaaa8596aedc18bf8c56b42fe8d/brick 
Brick3: 10.20.4.184:/var/lib/heketi/mounts/vg_0797a1d458309eec3e5e818a9b87f6c6/brick_2b5255cc2c0297e4e34eb6f1b4319fb9/brick 
Brick4: 10.20.6.239:/var/lib/heketi/mounts/vg_bd7fbf9053d6340771f7b75ce2872339/brick_c48d4ea4b43635f62c464ddf0259d733/brick 
Brick5: 10.20.4.184:/var/lib/heketi/mounts/vg_0797a1d458309eec3e5e818a9b87f6c6/brick_121fbc266c905311d8a8810f221fbdca/brick 
Brick6: 10.20.5.232:/var/lib/heketi/mounts/vg_c05319c8a95eaa083adbedb7d43913fa/brick_5f208c680444b4820f53c923aa079614/brick 
Options Reconfigured: transport.address-family: inet nfs.disable: on cluster.brick-multiplex: on 

Finally, with Container-Native Storage 3.6, we have expanded the amount of technical documentation available. We provide more examples of things both new and pre-existing that you can do with container-native storage, as well as detailed upgrade procedures from a variety of configurations to make sure you can get the latest set of features.

Verdict

The storage play for containers is an exciting space at the moment. There are many options available for customers, and Red Hat container-native storage is unique in the way it runs natively on OpenShift and provides scalable shared file, block, and object storage to business applications and container platform infrastructure.

Red Hat Ceph Storage: Object storage performance and sizing guide

Red Hat Ceph Storage is a proven, petabyte-scale, object storage solution designed to meet the scalability, cost, performance, and reliability challenges of large-scale, media-serving, savvy organizations. Designed for web-scale object storage and cloud infrastructures, Red Hat Ceph Storage delivers the scalable performance necessary for rich media and content-distribution workloads.

While most of us are familiar with deploying block or file storage, object storage expertise is less common. Object storage is an effective way to provision flexible and massively scalable data storage without the arbitrary limitations of traditional proprietary or scale-up storage solutions. Before building object storage infrastructure at scale, organizations need to understand how to best configure and deploy software, hardware, and network components to serve a range of diverse workloads. They also need to understand the performance and scalability they can expect from given hardware, software, and network configurations.

This reference architecture/performance and sizing guide describes Red Hat Ceph Storage coupled with QCT (Quanta Cloud Technology) storage servers and networking as object storage infrastructure. Testing, tuning, and performance are described for both large-object and small-object workloads. This guide also presents the results of the tests conducted to evaluate the ability of configurations to scale to host hundreds of millions of objects.

After hundreds of hours of [Test ⇒ Tune ⇒ Repeat] exercises, this reference architecture provides empirical answers to a range of performance questions surrounding Ceph object storage, such as (but not limited to):

  • What are the architectural considerations before designing object storage?
  • What networking is most performant for Ceph object storage?
  • What does performance look like with dedicated vs. co-located Ceph RGWs?
  • How many Ceph RGW nodes do I need?
  • How do I tune object storage performance?
  • What are the recommendations for small/large object workloads?
  • What should I do? I’ve got millions of objects to store.

And the list of questions goes on. You can unlock the performance secrets of Ceph object storage for your organization with the help of the Red Hat Ceph Storage/QCT performance and sizing guide.

Storage for RHV and OCP: Two Glusters on one platform

Architecture is an interesting discipline. There are whitepapers and best practices and reference architectures to offer pristine views of what your perfect deployment should look like. And then there are budgets and timelines and business requirements to derail all of that. It’s what makes this job so interesting and challenging—hacking together the best pieces of disparate and often seemingly unrelated systems to meet goals driven by six leaders whose bonuses are met by completely different metrics.

A recent project has involved combining OpenShift Container Platform (OCP), Red Hat Virtualization (RHV), and Red Hat Gluster Storage (Gluster) into a unified system with common lifecycle operations, minimized management points, and the lowest overall footprint in terms of both capital cost and TCO. The primary storage challenge here is in creating a Gluster environment to support both RHV and its VMs as well as OCP container persistent volume requirements.

Our architectural goals include:

  • Purchase a single flexible hardware platform to serve all the storage needs
  • Segregate Gluster for RHV and Gluster for OCP into separate pools for resource allocation and to avoid possible administration snafus (such as we experienced in early testing)
  • Maintain a single-point and single-method of management—one Heketi server to rule them all
  • Containerize as much as possible to keep lifecycle maintenance atomic

Our early version of the architecture had Gluster running as container-native storage (CNS) for OCP on top of RHV while also serving storage to RHV, but this proved to introduce a chicken-and-egg problem where a single failure (such as an etcd crash) could cause a cascading outage. So our redesign involved splitting Gluster off from OCP as a stand-alone system while still being a unified storage provider and leveraging container atomicity.

The approach we wanted involved containerized Gluster running on bare-metal container hosts. Fundamentally, this is actually pretty straightforward today with pre-build Gluster containers available from the Red Hat registry. What complicated this was our desire to run two separate containerized Gluster pools on the same hardware nodes.

Disclaimer

There’s a pretty good chance that this architecture is not explicitly supported by Red Hat. While all the components we use here are definitely supported, this particular combination is untested by our engineering, QE, and performance teams. Don’t consider anything here a recommendation for how you should run your environment, only an academic study of a possible approach to solving an interesting challenge. If you have any questions, please reach out to your Red Hat sales and support teams.

The platform

We initially wanted to build this on top of Red Hat Enterprise Linux Atomic Host, but our lab environment wasn’t setup to provision this build on our systems, so we had to go forward with RHEL plus the docker packages. For a production build, we would return to using Atomic.

Networking

Gluster containers are usually configured with host networking because they need to communicate freely with each other and need to serve storage out to other systems and containers. However, with host networking, the Gluster ports are bound to all interfaces, so it is not possible to run two Gluster containers in this mode due to port conflicts. To solve this, the networks for each Gluster pool had to be segregated.

First, a VLAN sub-interface was created on each Gluster node for the storage network interface and using VLAN ID 199. There are ifcfg files to make these persistent. So each node includes a 192.168.99.0/24 IP on the primary interface and a 192.168.199.0/24 IP on a VLAN sub-interface. The Switch ports for the storage network interfaces have been configured for the tagged VLAN ID 199. The 802.1q kernel module (for VLANs) was set to load at boot time on each node with a /etc/modules-load.d/8021q.conf file.

Containerized Gluster

Networks

Each Gluster container needs to exist on its own interface and subnet. So leveraging the system-level network stuff done above, the two interfaces were each attached to a docker macvlan network on each node.

docker network create -d macvlan --subnet=192.168.99.0/24 \

-o parent=eth1 gluster-rhv-net
docker network create -d macvlan --subnet=192.168.199.0/24 \

-o parent=eth1.199 gluster-ocp-net

Containers

The containers were pulled down from the Red Hat registry.

docker pull registry.access.redhat.com/rhgs3/rhgs-server-rhel7
docker pull registry.access.redhat.com/rhgs3/rhgs-volmanager-rhel7

The Gluster containers need to be privileged in order to access the /dev/sdX block devices. They also need a number of local persistent volume stores in order to ensure they start up properly each time.

The container fstab file needs a persistent mount. So first we should touch these files, otherwise the gluster-startup command in the container will fail.

touch /var/lib/heketi-{rhv,ocp}/fstab

Then we can run the containers.

docker run -d --privileged=true --net=gluster-rhv-net \

--ip=192.168.99.28  --name=gluster-rhv-1 -v /run \

-v /home/gluster-rhv-1-root:/root:z \

-v /etc/glusterfs-rhv:/etc/glusterfs:z \

-v /var/lib/glusterd-rhv:/var/lib/glusterd:z \

-v /var/log/glusterfs-rhv:/var/log/glusterfs:z \

-v /var/lib/heketi-rhv:/var/lib/heketi:z \

-v /sys/fs/cgroup:/sys/fs/cgroup:ro \

-v /dev:/dev rhgs3/rhgs-server-rhel7
docker run -d --privileged=true --net=gluster-ocp-net \

--ip=192.168.199.28 --name=gluster-ocp-1 -v /run \

-v /home/gluster-ocp-1-root:/root:z \

-v /etc/glusterfs-ocp:/etc/glusterfs:z \

-v /var/lib/glusterd-ocp:/var/lib/glusterd:z \

-v /var/log/glusterfs-ocp:/var/log/glusterfs:z \

-v /var/lib/heketi-ocp:/var/lib/heketi:z \

-v /sys/fs/cgroup:/sys/fs/cgroup:ro \

-v /dev:/dev rhgs3/rhgs-server-rhel7

Block device assignments

Running the containers in privileged mode allows them to access all system block devices. For our particular architectural needs, we intend to use from each node only one SSD for the gluster-rhv pool and the remaining five SSDs for the gluster-ocp pool.

 Gluster Pool  Block Devices
 gluster-rhv  sdb
 gluster-ocp  sdc, sdd, sde, sdf, sdg

Heketi

Config

The persistent Heketi config is being stored in the /etc/heketi directory on one of the nodes (we’ll call it node1). First, an ssh keypair is created and placed there.

ssh-keygen -f /etc/heketi/heketi_key -t rsa -N ''

Next, the heketi.json file is created. Right now, no auth is being used — obviously don’t do this in production. Note the ssh port is 2222, which is what the Gluster containers are configured to listen on.

{
  "_port_comment": "Heketi Server Port Number",
  "port": "8080",

  "_use_auth": "Enable JWT authorization. Please enable for deployment",
  "use_auth": false,

  "_jwt": "Private keys for access",
  "jwt": {
    "_admin": "Admin has access to all APIs",
    "admin": {
      "key": "My Secret"
    },
    "_user": "User only has access to /volumes endpoint",
    "user": {
      "key": "My Secret"
    }
  },

  "_glusterfs_comment": "GlusterFS Configuration",
  "glusterfs": {
    "_executor_comment": [
      "Execute plugin. Possible choices: mock, ssh",
      "mock: This setting is used for testing and development.",
      "      It will not send commands to any node.",
      "ssh:  This setting will notify Heketi to ssh to the nodes.",
      "      It will need the values in sshexec to be configured.",
      "kubernetes: Communicate with GlusterFS containers over",
      "            Kubernetes exec api."
    ],
    "executor": "ssh",

    "_sshexec_comment": "SSH username and private key file information",
    "sshexec": {
      "keyfile": "/etc/heketi/heketi_key",
      "user": "root",
      "port": "2222"
    },

    "_db_comment": "Database file name",
    "db": "/var/lib/heketi/heketi.db",

    "_loglevel_comment": [
      "Set log level. Choices are:",
      "  none, critical, error, warning, info, debug",
      "Default is warning"
    ],
    "loglevel" : "debug"
  }
}

SSH access

The Heketi server needs passwordless SSH access to all Gluster containers on port 2222. The public key generated above needs to be added to the authorized_keys for all of the Gluster containers. Note that we have a local persistent volume (PV) for each Gluster container’s /root directory, so this authorized_key entry was simply added to each one of those.

cat /etc/heketi/heketi_key.pub >> \

/home/gluster-rhv-1-root/.ssh/authorized_keys

NOTE: This needs to be done for each of the root home directories for each Gluster container

Container

The single Heketi container will run on node1. It needs access to both of the subnets, so the best thing to do is run the container in host networking mode. It also needs a few persistent volumes.

docker run -d --net=host --name=gluster-heketi \

-v /etc/heketi:/etc/heketi:z -v /var/lib/heketi:/var/lib/heketi:z \

rhgs3/rhgs-volmanager-rhel7

Network

Since we are running heketi-cli on the same node that we are running the Heketi container, there is a security issue we have to work through. By default, the container host cannot directly access the local container via the IP assigned to its macvlan network interface. So on the container host node1 we need to create local macvlan interfaces for each of the subnets. Use this at runtime and the /etc/rc.d/rc.local file:

/usr/sbin/ip link add macvlan0 link eth1 type macvlan mode bridge
/usr/sbin/ip addr add 192.168.99.228/24 dev macvlan0
/usr/sbin/ifconfig macvlan0 up

/usr/sbin/ip link add macvlan1 link eth1.199 type macvlan mode bridge
/usr/sbin/ip addr add 192.168.199.228/24 dev macvlan1
/usr/sbin/ifconfig macvlan1 up

The rc.local file in RHEL is for legacy support, so it has to be made executable and its systemd service has to be enabled.

chmod 755 /etc/rc.d/rc.local
systemctl enable rc-local.service

Heketi CLI

The heketi-cli needs to run $somewhere. For simplicity, the RPM is installed on node1. With the container running with networking in host mode, heketi is listening on localhost port 8080. Export the environment variable in order to be able to run heketi-cli commands.

export HEKETI_CLI_SERVER=http://localhost:8080

Setting up the Heketi clusters

A JSON file is populated at /root/heketi-rhv-plus-ocp-topology.json on node1. This file defines two separate Heketi clusters with their respective Gluster nodes (containers) and block devices.

{
    "clusters": [
        {
            "nodes": [
                {
                    "node": {
                        "hostnames": {
                            "manage": [
                                "192.168.99.28"
                            ],
                            "storage": [
                                "192.168.99.28"
                            ]
                        },
                        "zone": 1
                    },
                    "devices": [
                        "/dev/sdb"
                    ]
                },
                {
                    "node": {
                        "hostnames": {
                            "manage": [
                                "192.168.99.29"
                            ],
                            "storage": [
                                "192.168.99.29"
                            ]
                        },
                        "zone": 2
                    },
                    "devices": [
                        "/dev/sdb"
                    ]
                },
                {
                    "node": {
                        "hostnames": {
                            "manage": [
                                "192.168.99.30"
                            ],
                            "storage": [
                                "192.168.99.30"
                            ]
                        },
                        "zone": 3
                    },
                    "devices": [
                        "/dev/sdb"
                    ]
                }
            ]
        },

        {
            "nodes": [
                {
                    "node": {
                        "hostnames": {
                            "manage": [
                                "192.168.199.28"
                            ],
                            "storage": [
                                "192.168.199.28"
                            ]
                        },
                        "zone": 1
                    },
                    "devices": [
                        "/dev/sdc",
                        "/dev/sdd",
                        "/dev/sde",
                        "/dev/sdf",
                        "/dev/sdg"
                    ]
                },
                {
                    "node": {
                        "hostnames": {
                            "manage": [
                                "192.168.199.29"
                            ],
                            "storage": [
                                "192.168.199.29"
                            ]
                        },
                        "zone": 2
                    },
                    "devices": [
                        "/dev/sdc",
                        "/dev/sdd",
                        "/dev/sde",
                        "/dev/sdf",
                        "/dev/sdg"
                    ]
                },
                {
                    "node": {
                        "hostnames": {
                            "manage": [
                                "192.168.199.30"
                            ],
                            "storage": [
                                "192.168.199.30"
                            ]
                        },
                        "zone": 3
                    },
                    "devices": [
                        "/dev/sdc",
                        "/dev/sdd",
                        "/dev/sde",
                        "/dev/sdf",
                        "/dev/sdg"
                    ]
                }
            ]
        }
    ]
}

This file is passed (once) to Heketi to setup the two clusters.

heketi-cli topology load --json=heketi-rhv-plus-ocp-topology.json

It’s important to note the two different clusters. It’s not (AFAIK) possible to “name” the clusters, so we have to reference them by their UUIDs. The Gluster volumes for RHV will be created on one cluster, and those orchestrated for OCP PVs will be created on a different cluster.

RHV Gluster volumes

For the purposes of RHV, two volumes were requested—one for the Hosted Engine and one for the VM storage. These were created via heketi-cli. Note the cluster ID passed to the commands.

heketi-cli volume create --size 100 --name rhv-hosted-engine \

--clusters ae2a309d02781816adfed567693221a9
heketi-cli volume create --size 1024 --name rhv-virtual-machines \

--clusters ae2a309d02781816adfed567693221a9

These can be mounted to the RHV nodes via the 192.168.99.0/24 subnet using the Gluster native client. Example fstab entries:

192.168.99.28:rhv-hosted-engine      /100g   glusterfs       backupvolfile-server=192.168.99.29:192.168.99.30 0 0
192.168.99.28:rhv-virtual-machines      /1t   glusterfs       backupvolfile-server=192.168.99.29:192.168.99.30 0 0

OCP PV Gluster volumes

Our OCP pods are attached to the 192.168.199.0/24 subnet to communicate with the storage. First on node1 the Heketi API port (8080) needs to be opened in the firewall.

firewall-cmd --add-port 8080/tcp
firewall-cmd --add-port 8080/tcp --permanent

Then the storage class for OCP is defined with the below YAML. Note that we aren’t currently doing any authentication (but obviously we should). You see here that we explicitly define the Heketi cluster ID for this class in order to ensure that all volumes for PVCs are created only on the Gluster pool we have identified for OCP use.

kind: StorageClass
apiVersion: storage.k8s.io/v1beta1
metadata:
 name: gluster-dyn
provisioner: kubernetes.io/glusterfs
parameters:
 resturl: "http://192.168.199.128:8080"
 restauthenabled: "false"
 clusterid: "74edade536c80f14486edfbabd204151"

Then the storage class is added to OCP on the master.

oc create -f glusterfs-storageclass.yaml

From this point, PVCs (persistent volume claims) made against this storage class will interface with Heketi to dynamically provision Gluster volumes to match the claim.

Miscellaneous

Auto-start containers

Docker container systemd init scripts are tricky. I’ve found that every example on the internet is either wrong, outdated, or uses an approach I don’t like.

Below is an example systemd service file for the Heketi container, which is simple and works the way we expect it to with the docker run command in the ExecStart (/etc/systemd/system/docker-container-gluster-heketi.service). NOTE: Do not daemonize (-d) the docker run command in the init script. Also, the SuccessExitStatus is important here.

[Unit]
Description=Gluster Heketi Container
Requires=docker.service
After=docker.service

[Service]
TimeoutStartSec=60
Restart=on-abnormal
SuccessExitStatus=0 137
ExecStartPre=-/usr/bin/docker stop gluster-heketi
ExecStartPre=-/usr/bin/docker rm gluster-heketi
ExecStart=/usr/bin/docker run --net=host --name=gluster-heketi -v /etc/heketi:/etc/heketi:z -v /var/lib/heketi:/var/lib/heketi:z rhgs3/rhgs-volmanager-rhel7
ExecStop=/usr/bin/docker stop gluster-heketi

[Install]
WantedBy=multi-user.target

Reload the systemd daemon:

systemctl daemon-reload

Enable and start the service

systemctl enable docker-container-gluster-heketi

systemctl start docker-container-gluster-heketi

Known issues and TODOs

  • Security needs to be taken into account. We’ll set up appropriate key-based authentication and JWT for Heketi. We’d also like to use role-based auth. Hopefully we’ll cover this in a future blog post.
  • Likely $other_things I haven’t realized yet, or better ways of approaching this. I’d love to hear your comments.

Library of Ceph and Gluster reference architectures – Simplicity on the other side of complexity

The Storage Solution Architectures team at Red Hat develops reference architectures, performance and sizing guides, and test drives for Gluster- and Ceph-based solutions. We’re a group of architects who perform lab validation, tuning, and interoperability development for composable storage services with target workloads on optimized server and network configurations. We seek simplicity on the other side of complexity.

At the end of this blog entry is a full library of our current publications and test drives.

In our modern era, a top company asset is pivotability. Pivotability based on external market changes. Pivotability after unknowns become known. Pivotability after golden ideas become dark alleys. For most enterprises, pivotability requires a composable technology infrastructure for shifting resources to meet changing needs. Composable storage services, such as those provided by Ceph and Gluster, are part of many companies’ composable infrastructures.

Composable technology infrastructures are most frequently described by the following attributes:

  • Open source v. closed development.
  • On-demand architectures v. fixed architectures.
  • Commodity hardware v. proprietary appliances.
  • Cross-industry collaboration v. isolated single-vendor silos.

As noted in the following figure, a few companies with large staffs of in-house experts can create composable infrastructures from raw technologies. Their large investments in in-house expertise allows them to convert raw technologies into solutions with limited pre-integration by technology suppliers. AWS, Google, and Azure are all examples of DIY businesses. A larger number of other companies, also needing composable infrastructures, rely on technology suppliers and the community for solution pre-integration and guidance to reduce their in-house expertise costs. We’ll label them “Assisted DIY.” Finally, the majority of global enterprises lack the in-house expertise for deploying these composable infrastructures. They rely on public cloud providers and pre-packaged solutions for their infrastructure needs. We’ll call them “Pre-packaged.”

Brent_Slide

The reference architectures, performance and sizing guides, and test drives produced by our team are primarily focused on the “Assisted DIY” segment of companies. Additionally, we strive to make Gluster and Ceph composable storage services available to the “Pre-packaged” segment of companies by using what we learn to produce pre-packaged combinations of Red Hat software with partner hardware targeting specific workload use cases.

We enjoy our roles at Red Hat because of the many of you with whom we collaborate to produce value.  We hope you find these guides useful.

Team-produced with partner collaboration:

Partner-produced with team collaboration:

Pre-packaged solutions:

Hands-on test drives:

Struggling to containerize stateful applications in the cloud? Here’s how.

The newest release of Red Hat’s Reference Architecture “OpenShift Container Platform 3.5 on Amazon Web Services” now incorporates container-native storage, a unique approach based on Red Hat Gluster Storage to avoid lock-in, enable stateful applications, and simplify those applications’ high availability.


In the beginning, everything was so simple. Instead of going through the bureaucracy and compliance-driven process of requesting compute, storage, and networking resources, I would pull out my corporate credit card and register at the cloud provider of my choice. Instead of spending weeks forecasting the resource needs and costs of my newest project, I would get started in less than 1 hour. Much lower risk, virtually no capital expenditure for my newest pet project. And seemingly endless capacity—well, as long as my credit card was covered. If my project didn’t turn out to be a thing, I didn’t end up with excess infrastructure, either.

Until I found out that basically what I was doing was building my newest piece of software against a cloud mainframe. Not directly, of course. I was still operating on top of my operating system with the libraries and tools of my choice, but essentially I spend significant effort getting to that point with regards to orchestration and application architecture. And these are not easily ported to another cloud provider.

I realize that cloud providers are vertically integrated stacks, just as mainframes were. Much more modern and scalable with an entirely different cost structure—but, still, eventually and ultimately, lock-in.

Avoid provider lock-in with OpenShift Container Platform

This is where OpenShift comes in. I take orchestration and development cycles to a whole new level when I stop worrying about operating system instances, storage capacity, network overlays, NAT gateways, firewalls—all the things I need to make my application accessible and provide value.

Instead, I deal with application instances, persistent volumes, services, replication controllers, and build configurations—things that make much more sense to me as an application developer as they are closer to what I am really interested in: deploying new functionality into production. Thus, OpenShift offers abstraction on top of classic IT infrastructure and instead provides application infrastructure. The key here is massive automation on top of the concept of immutable infrastructure, thereby greatly enhancing the capability to bring new code into production.

The benefit is clear: Once I have OpenShift in place, I don’t need to worry about any of the underlying infrastructure—I don’t need to be aware of whether I am actually running on OpenStack, VMware, Azure, Google Cloud, or Amazon Web Services (AWS). My new common denominator is the interface of OpenShift powered by Kubernetes, and I can forget about what’s underneath.

Well, not quite. While OpenShift provides a lot of drivers for various underlying infrastructure, for instance storage, they are all somewhat different. Their availability, performance, and feature set is tied to the underlying provider, for instance Elastic Block Storage (EBS) on AWS. I need to make sure that critical aspects of the infrastructure below OpenShift are reflected in OpenShift topology. A good example are AWS availability zones (AZs): They are failure domains in a region across which an application instance should be distributed to avoid downtime in the event a single AZ is lost. So OpenShift nodes need to be deployed in multiple AZs.

This is where another caveat comes in: EBS volumes are present only inside a single AZ. Therefore, my application must replicate the data across other AZs if it uses EBS to store it.

So there are still dependencies and limitations a developer or operator must be aware of, even if OpenShift has drivers on board for EBS and will take care about provisioning.

Introducing container-native storage

With container-native storage (CNS), we now have a robust, scalable, and elastic storage service out-of-the-box for OpenShift Container Platform—based on Red Hat Gluster Storage. The trick: GlusterFS runs containerized on OpenShift itself. Thus, it runs on any platform that OpenShift is supported on—which is basically everything, from bare metal, to virtual, to private and public cloud.

With CNS, OpenShift gains a consistent storage feature set across, and independent of, all supported cloud providers. It’s deployed with native OpenShift / Kubernetes resources, and GlusterFS ends up running in pods as part of a DaemonSet:

[ec2-user@ip-10-20-4-55 ~]$ oc get pods
NAME              READY     STATUS    RESTARTS   AGE
glusterfs-0bkgr   1/1       Running   9          7d
glusterfs-4fmsm   1/1       Running   9          7d
glusterfs-bg0ls   1/1       Running   9          7d
glusterfs-j58vz   1/1       Running   9          7d
glusterfs-qpdf0   1/1       Running   9          7d
glusterfs-rkhpt   1/1       Running   9          7d
heketi-1-kml8v    1/1       Running   8          7d

The pods are running in privileged mode to access the nodes’ block device directly. Furthermore, for optimal performance, the pods are using host-networking mode. This way, OpenShift nodes are running a distributed, software-defined, scale-out file storage service, just as any distributed micro-service application.

There is an additional pod deployed that runs heketi—a RESTful API front end for GlusterFS. OpenShift natively integrates via a dynamic storage provisioner plug-in with this service to request and delete storage volumes on behalf of the user. In turn, heketi controls one or more GlusterFS Trusted Storage Pools.

Container-native storage on Amazon Web Services

The EBS provisioner has been available for OpenShift for some time. To understand what changes with CNS on AWS, a closer look at how EBS is accessible to OpenShift is in order.

  1. Dynamic provisioning
    EBS volumes are dynamically created and deleted as part of storage provisioning requests (PersistentVolumeClaims) in OpenShift.
    .
  2. Local block storage
    EBS appears to the EC2 instances as a local block device. Once provisioned, it is attached to the EC2 instance, and a PCI interrupt is triggered to inform the operating system.

    NAME                                  MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
    xvda                                  202:0    0   15G  0 disk
    ├─xvda1                               202:1    0    1M  0 part
    └─xvda2                               202:2    0   15G  0 part /
    xvdb                                  202:16   0   25G  0 disk
    └─xvdb1                               202:17   0   25G  0 part
      ├─docker_vol-docker--pool_tmeta     253:0    0   28M  0 lvm
      │ └─...                             253:2    0 23.8G  0 lvm
      │   ├─...                           253:8    0    3G  0 dm
      │   └─...                           253:9    0    3G  0 dm
      └─docker_vol-docker--pool_tdata     253:1    0 23.8G  0 lvm
        └─docker_vol-docker--pool         253:2    0 23.8G  0 lvm
          ├─...                           253:8    0    3G  0 dm
          └─...                           253:9    0    3G  0 dm
    xvdc                                  202:32   0   50G  0 disk 
    xvdd                                  202:48   0  100G  0 disk

    OpenShift on AWS also uses EBS to back local docker storage. EBS storage is formatted with a local filesystem like XFS..

  3. Not shared storage
    EBS volumes cannot be attached to more than one EC2 instance. Thus, all pods mounting an EBS-based PersistentVolume in OpenShift must run on the same node. The local filesystem on top of the EBS block device does not support clustering either.
    .
  4. AZ-local storage
    EBS volumes cannot cross AZs. Thus, OpenShift cannot failover pods mounting EBS storage into different AZs. Basically, an EBS volume is a failure domain.
    .
  5. Performance characteristics
    The type of EBS storage, as well as capacity, must be selected up front. Specifically, for fast storage a certain minimum capacity must be requested to have a minimum performance level in terms of IOPS.

This is the lay of the land. While these characteristics may be acceptable for stateless applications that only need to have local storage, they become an obstacle for stateful applications.

People want to containerize databases, as well. Following a micro-service architecture where every service maintains its own state and data model, this request will become more common. The nature of these databases differs from the classic, often relational, database management system IT organizations have spent millions on: They are way smaller and store less data than their big brother from the monolithic world. Still, with the limitations of EBS, I would need to architect replication and database failover around those just to deal with a simple storage failure.

Here is what changes with CNS:

  1. Dynamic provisioning
    The user experience actually doesn’t change. CNS is represented like any storage provider in OpenShift, by a StorageClass. PersistentVolumeClaims (PVCs) are issued against it, and the dynamic provisioner for GlusterFS creates the volume and returns it as a PersistentVolume (PV). When the PVC is deleted, the GlusterFS volume is deleted, as well.
    .
  2. Distributed file storage on top of EBS
    CNS volumes are basically GlusterFS volumes, managed by heketi. The volumes are built out of local block devices of the OpenShift nodes backed by EBS. These volumes provide shared storage and are mounted on the OpenShift nodes with the GlusterFS FUSE client.

    [ec2-user@ip-10-20-5-132 ~]$ mount
    ...
    10.20.4.115:vol_0b801c15b2965eb1e5e4973231d0c831 on /var/lib/origin/openshift.local.volumes/pods/80e27364-2c60-11e7-80ec-0ad6adc2a87f/volumes/kubernetes.io~glusterfs/pvc-71472efe-2a06-11e7-bab8-02e062d20f83 type fuse.glusterfs (rw,relatime,user_id=0,group_id=0,default_permissions,allow_other,max_read=131072)
    ...
  3. Container-shared storage
    Multiple pods can mount and write to the same volume. The access mode for the corresponding node is known as “RWX”—read-write many. The containers can run on different OpenShift nodes, and the dynamic provisioner will mount the GlusterFS volume on the right nodes accordingly. Then, this local mount directory is bind-mounted to the container.
    .
  4. Cross-availability zone
    CNS is deployed across AWS AZs. The integrated, synchronous replication of GlusterFS will mirror every write 3 times. GlusterFS is deployed across OpenShift nodes in at least different AZs, and thus the storage is available in all zones. The failure of a single GlusterFS pod, an OpenShift node running the pod, or a block device accessed by the pod will have no impact. Once the failed resources come back, the storage is automatically re-replicated. CNS is actually aware of the failure zones as part of the cluster topology and will schedule new volumes, as well as recovery, so that there is no single point of failure.
    .
  5. Predictable performance
    CNS storage performance is not tied to the size of storage request by the user in OpenShift. It’s the same performance whether 1GB or 100GB PVs are requested.
    .
  6. Storage performance tiers
    CNS allows for multiple GlusterFS Trusted Storage Pools to be managed at once. Each pool consists of at least 3 OpenShift nodes running GlusterFS pods. While the OpenShift nodes belong to a single OpenShift cluster, the various GlusterFS pods form their own Trusted Storage Pools. An administrator can use this to equip the nodes with different kinds of storage and offer their pools with CNS as distinct storage tiers in OpenShift, via its own StorageClass. An administrator instance might, for example, run CNS on 3 OpenShift nodes with SSD (e.g., EBS gp2) storage and call it “fast,” whereas another set of OpenShift nodes with magnetic storage (e.g., EBS st1) runs a separate set of GlusterFS pods as an independent Trusted Storage Pool, represented with a StorageClass called “capacity.”

This is a significant step toward simplifying and abstracting provider infrastructure. For example, a MySQL database service running on top of OpenShift is now able to survive the failure of an AWS AZ, without needing to set up MySQL Master-Slave replication or change the micro-service to replicate data on its own.

Storage provided by CNS is efficiently allocated and provides performance with the first Gigabyte provisioned, thereby enabling storage consolidation. For example, consider six MySQL database instances, each in need of 25 GiB of storage capacity and up to 1500 IOPS at peak load. With EBS, I would create six EBS volumes, each with at least 500 GiB capacity out of the gp2 (General Purpose SSD) EBS tier, in order to get 1500 IOPS guaranteed. Guaranteed performance is tied to provisioned capacity with EBS.
With CNS, I can achieve the same using only 3 EBS volumes at 500 GiB capacity from the gp2 tier and run these with GlusterFS. I would create six 25 GiB volumes and provide storage to my databases with high IOPS performance, provided they don’t peak all at the same time.

Doing that, I would halve my EBS cost and still have capacity to spare for other services. My read IOPS performance is likely even higher because in CNS with 3-way replication I would read from data distributed across 3×1500 IOPS gp2 EBS volumes.

Finally, the setup for CNS is very simple and can run on any OpenShift installation based on version 3.4 or newer.

This way, no matter where I plan to run OpenShift (i.e., which cloud provider currently offers lowest prices), I can rely on the same storage features and performance. Furthermore, the Storage Service grows with the OpenShift cluster but still provides elasticity. Only a subset of OpenShift nodes must run CNS, at least 3 ideally across 3 AZs.

Deploying container-native storage on AWS

Installing OpenShift on AWS is dramatically simplified based on the OpenShift on Amazon Web Services Reference Architecture. A set of Ansible playbooks augments the existing openshift-ansible installation routine and creates all the required AWS infrastructure automatically.

A simple python script provides a convenient wrapper to the playbooks found in the openshift-ansible-contrib repository on GitHub for deploying on AWS.

All the heavy lifting of setting up Red Hat OpenShift Container Platform on AWS is automated with best practices incorporated.

The deployment finishes with an OpenShift Cluster with 3 master nodes, 3 infrastructure nodes, and 2 application nodes deployed in a highly available fashion across AWS AZs. The external and internal traffic is load balanced, and all required network, firewall, and NAT resources are stood up.

Since version 3.5, the reference architecture playbooks now ship with additional automation to make deployment of CNS as easy. Through additional AWS CloudFormation templates and Ansible playbook tasks, the additional, required infrastructure is stood up. This mainly concerns provisioning of additional OpenShift nodes with an amended firewall configuration, additional EBS volumes, and then joining them to the existing OpenShift cluster.

In addition, compared to previous releases, the CloudFormation templates now emit more information as part of the output. These are picked up by the playbooks to further reduce the information needed from the administrator. They will simply get the right information from the existing CloudFormation stack to retrieve the proper integration points.

The result is AWS infrastructure ready for the administrator to deploy CNS. Most of the manual steps of this process can therefore be avoided. Three additional app nodes are deployed with configurable instance type and EBS volume type. Availability zones of the selected AWS region are taken into account.

Subsequent calls allow for provisioning of additional CNS pools. The reference architecture makes reasonable choices for the EBS volume type and the EC2 instance with a balance between running costs and initial performance. The only thing left for the administrator to do is to run the cns-deploy utility and create a StorageClass object to make the new storage service accessible to users.

At this point, the administrator can choose between labeling the nodes as regular application nodes or provide a storage-related label that would initially exclude them from the OpenShift scheduler for regular application pods.

Container-ready storage

The reference architecture also incorporates the concept of Container-Ready Storage (CRS). In this deployment flavor, GlusterFS runs on dedicated EC2 instances with a heketi-instance deployed separately, both running without containers as ordinary system services. The difference is that these instances are not part of the OpenShift cluster. The storage service is, however, made available to, and used by, OpenShift in the same way. If the user, for performance or cost reasons, wants the GlusterFS storage layer outside of OpenShift, this is made possible with CRS. For this purpose, the reference architecture ships add-crs-storage.py to automate the deployment in the same way as for CNS.

Verdict

CNS provides further means of OpenShift Container Platform becoming an equalizer for application development. Consistent storage services, performance, and management are provided independently of the underlying provider platform. Deployment of data-driven applications is further simplified with CNS as the backend. This way, not only stateless but also stateful applications become easy to manage.

For developers, nothing changes: The details of provisioning and lifecycle of storage capacity for containerized applications is transparent to them, thanks to CNS’s integration with native OpenShift facilities.

For administrators, achieving cross-provider, hybrid-cloud deployments just became even easier with the recent release of the OpenShift Container Platform 3.5 on Amazon Web Service Reference Architecture. With just two basic commands, an elastic and fault-tolerant foundation for applications can be deployed. Once set up, growth becomes a matter of adding nodes.

It is now possible to choose the most suitable cloud provider platform without worrying about various tradeoffs between different storage feature sets or becoming too close to one provider’s implementation, thereby avoiding lock-in long term.

The reference architecture details the deployment and resulting topology. Access the document here.