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.
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