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Adding persistance to on premises Kubernetes cluster

The following is part of a series of posts I wrote called "Repurposing old equipment by building a Kubernetes cluster".

While old equipment by itself is in general not very useful unless you find a particular use case, by combining a number of old devices you can build a more powerful system that can span perhaps a number of use cases. Kubernetes is a perfect candidate to be able to do this. I had a number of old laptops laying about and decided to test this theory out.

One of the more difficult things with Kubernetes is correctly setting up persistance for stateful services. The abstractions provided with storage classes, volume claims etc help a lot, but in most cases you’re going to need to do some vendor specific setup. i.e. Running on GKE means you’ll likely be using a gcePersistentDisk in your PersistentVolume.

With on premises, we could use something like Rook but I’m looking to keep things simple this time round and therefore I feel that the best choice is going with a NFS storage solution.

Before starting, I want the NFS provisioner to be the default storage class for any future requirements. To do this, I need to enable the DefaultStorageClass admission plugin. This is done by editing the /etc/kubernetes/manifests/kube-apiserver.yaml file on the master node, and adding DefaultStorageClass to the comma separated values on the --enable-admission-plugins line.

kubelet supposedly watches these file periodically for changes which I feel is not very declarative or a normal approach with Kubernetes. Not really sure on how to check the changes, although when I
look at the kube-apiserver pod, it appears to have been running only a few minutes which would suggest the update has taken place pretty much immediately after I saved the configuration file. Great!

Once this is done, it should mean that the storageclass.kubernetes.io/is-default-class annotation on the StorageClass we’re about to create means that any PersistentVolumeClaim with an empty StorageClass will automatically get an NFS volume provisioned.

One last thing here prior to adding the storage configuration to the cluster is that each node needs nfs-common installed at the OS level in order to mount nfs volumes, so at this point I run the following on all machines in the cluster to install nfs-common.

sudo apt-get install -y nfs-common

Alright, time to apply the storage configuration to the cluster.

---
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: nfs-provisioner-runner
rules:
  - apiGroups: [""]
    resources: ["persistentvolumes"]
    verbs: ["get", "list", "watch", "create", "delete"]
  - apiGroups: [""]
    resources: ["persistentvolumeclaims"]
    verbs: ["get", "list", "watch", "update"]
  - apiGroups: ["storage.k8s.io"]
    resources: ["storageclasses"]
    verbs: ["get", "list", "watch"]
  - apiGroups: [""]
    resources: ["events"]
    verbs: ["create", "update", "patch"]
  - apiGroups: [""]
    resources: ["services", "endpoints"]
    verbs: ["get"]
  - apiGroups: ["extensions"]
    resources: ["podsecuritypolicies"]
    resourceNames: ["nfs-provisioner"]
    verbs: ["use"]
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: run-nfs-provisioner
subjects:
  - kind: ServiceAccount
    name: nfs-provisioner
    namespace: default
roleRef:
  kind: ClusterRole
  name: nfs-provisioner-runner
  apiGroup: rbac.authorization.k8s.io
---
kind: Role
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: leader-locking-nfs-provisioner
rules:
  - apiGroups: [""]
    resources: ["endpoints"]
    verbs: ["get", "list", "watch", "create", "update", "patch"]
---
kind: RoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: leader-locking-nfs-provisioner
subjects:
  - kind: ServiceAccount
    name: nfs-provisioner
    namespace: default
roleRef:
  kind: Role
  name: leader-locking-nfs-provisioner
  apiGroup: rbac.authorization.k8s.io
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: nfs-provisioner
---
kind: Service
apiVersion: v1
metadata:
  name: nfs-provisioner
  labels:
    app: nfs-provisioner
spec:
  ports:
    - name: nfs
      port: 2049
    - name: mountd
      port: 20048
    - name: rpcbind
      port: 111
    - name: rpcbind-udp
      port: 111
      protocol: UDP
  selector:
    app: nfs-provisioner
---
kind: Deployment
apiVersion: apps/v1
metadata:
  name: nfs-provisioner
spec:
  selector:
    matchLabels:
      app: nfs-provisioner
  replicas: 1
  strategy:
    type: Recreate 
  template:
    metadata:
      labels:
        app: nfs-provisioner
    spec:
      serviceAccount: nfs-provisioner
      containers:
        - name: nfs-provisioner
          image: quay.io/kubernetes_incubator/nfs-provisioner:latest
          ports:
            - name: nfs
              containerPort: 2049
            - name: mountd
              containerPort: 20048
            - name: rpcbind
              containerPort: 111
            - name: rpcbind-udp
              containerPort: 111
              protocol: UDP
          securityContext:
            capabilities:
              add:
                - DAC_READ_SEARCH
                - SYS_RESOURCE
          args:
            - "-provisioner=home.com/nfs"
          env:
            - name: POD_IP
              valueFrom:
                fieldRef:
                  fieldPath: status.podIP
            - name: SERVICE_NAME
              value: nfs-provisioner
            - name: POD_NAMESPACE
              valueFrom:
                fieldRef:
                  fieldPath: metadata.namespace
          imagePullPolicy: "IfNotPresent"
          volumeMounts:
            - name: export-volume
              mountPath: /export
      volumes:
        - name: export-volume
          hostPath:
            path: /mnt/ssd/nfs
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
            - matchExpressions:
              - key: kubernetes.io/hostname
                operator: In
                values:
                - acepc
---
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: nfs-sc
  annotations:
    storageclass.kubernetes.io/is-default-class: true
provisioner: home.com/nfs
mountOptions:
  - vers=4.1

While it’s quite a large and involved configuration but if you read through it, there isn’t anything too complex or special in what it’s doing. Most of the configuration is related to setting up RBAC roles and bindings. The main points are:

  • the provisioner name which is passed in can be anything. I’ve decided to just use home.com in this instance because I couldn’t think up anything super intelligent when I put together the configuration.
  • We’re passing in a bunch of information about the pod directly as envvars as the nfs-provisioner container requires them.
  • We’re setting up a node affinity with the node with hostname acepc.

The reason for setting up affinity with acepc for this pod is due to the fact that acepc has a 250GB SSD installed.

250GB SSD installed in acepc

For the moment I’m only using this drive for persistance, but in future I could add further drives attached to different nodes and set up other deployments to target the nodes that the new drives are attached to.

At this point I check that everything deployed ok, and there appears to be an error. The path of /mnt/ssd/nfs doesn’t appear to exist. I quickly ssh into acepc directly and create the missing nfs directory, delete the current pod to trigger the replication controller to re-create the pod and after a few seconds, everything is up and running.

All looking good. Now to test it out. I choose to make a MySQL deployment to see what happens.

---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: nfs-mysql-test-pvc
spec:
  storageClassName: nfs-sc
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 1Gi
---
apiVersion: v1
kind: Service
metadata:
  name: mysql
spec:
  ports:
  - port: 3306
    targetPort: 3306
    protocol: TCP
  selector:
    app: mysql
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: mysql
spec:
  selector:
    matchLabels:
      app: mysql
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: mysql
    spec:
      containers:
      - image: mysql:5.6
        name: mysql
        env:
        - name: MYSQL_ROOT_PASSWORD
          value: password
        ports:
        - containerPort: 3306
          name: mysql
        volumeMounts:
        - name: mysql-storage
          mountPath: /var/lib/mysql
      volumes:
      - name: mysql-storage
        persistentVolumeClaim:
          claimName: nfs-mysql-test-pvc

I apply the above configuration and after a few minutes take a look at the persistent volumes, in Dashboard. Wowsers, there is a dynamically created volume now created for the MySQL deployment that I just launched.

NFS Dynamic Persistent Volume

Awesome, this means that anything requiring persistence I can now dynamically provision based on the requirements. It’s worth mentioning at this point that the PersistentVolumeClaim sets an explicit storageClassName, so I haven’t tested if the default storage class functionality has worked as yet.

Time to test it out MySQL in this context. I forward the MySQL instance to my local machine and connect to it via MySQL workbench.

$ kubectl get pods
NAME                                                     READY   STATUS    RESTARTS   AGE
mysql-64d7f649b-mpnjx                                    1/1     Running   0          109s
nfs-provisioner-78495f4f78-4qgcg                         1/1     Running   0          33m
weave-scope-agent-weave-scope-test-68mwl                 1/1     Running   0          20h
weave-scope-agent-weave-scope-test-f5m8h                 1/1     Running   0          20h
weave-scope-agent-weave-scope-test-mrjt8                 1/1     Running   0          20h
weave-scope-agent-weave-scope-test-mvptk                 1/1     Running   0          20h
weave-scope-agent-weave-scope-test-x9rgp                 1/1     Running   0          20h
weave-scope-agent-weave-scope-test-xzv6l                 1/1     Running   0          20h
weave-scope-frontend-weave-scope-test-78d78cf9fd-5ql92   1/1     Running   0          20h

$ kubectl port-forward mysql-64d7f649b-mpnjx 3306:3306
Forwarding from 127.0.0.1:3306 -> 3306
Forwarding from [::1]:3306 -> 3306
Handling connection for 3306

That takes care of the forwarding, and opening up workbench, I start a new session against localhost:3306, put the password in that we set earlier in the deployment, and it connects.

I create a new schema and table in workbench and populate the table with some test data. All works smoothly. As this is my first time setting up NFS, I want to dig a little deeper. Lets check out the actual volume mount position. I ssh into acepc and go to the /mnt/ssd/nfs directory.

[email protected]:/mnt/ssd/nfs$ ls -la
total 32
drwxr-xr-x 3 root root   4096 Sep  3 16:14 .
drwxr-xr-x 4 root root   4096 Sep  3 08:09 ..
-rw-r--r-- 1 root root   9898 Sep  3 16:15 ganesha.log
-rw------- 1 root root     36 Sep  3 14:50 nfs-provisioner.identity
drwxrwsrwx 5  999 docker 4096 Sep  3 16:16 pvc-0c9221bc-1589-45be-8350-0403378bdceb
-rw------- 1 root root    902 Sep  3 16:14 vfs.conf

[email protected]:/mnt/ssd/nfs$ cd pvc-0c9221bc-1589-45be-8350-0403378bdceb/

[email protected]:/mnt/ssd/nfs/pvc-0c9221bc-1589-45be-8350-0403378bdceb$ ls -la
total 176152
drwxrwsrwx 5  999 docker     4096 Sep  3 16:16 .
drwxr-xr-x 3 root root       4096 Sep  3 16:14 ..
-rw-rw---- 1  999 docker       56 Sep  3 16:15 auto.cnf
-rw-rw---- 1  999 docker 79691776 Sep  3 16:19 ibdata1
-rw-rw---- 1  999 docker 50331648 Sep  3 16:19 ib_logfile0
-rw-rw---- 1  999 docker 50331648 Sep  3 16:15 ib_logfile1
drwx--S--- 2  999 docker     4096 Sep  3 16:15 mysql
drwx--S--- 2  999 docker     4096 Sep  3 16:18 new_schema
drwx--S--- 2  999 docker     4096 Sep  3 16:15 performance_schema

That looks how I’d expect. We can see the directory for the volume claim there and internally it is most definitely a MySQL database.

Lets see if the data is hosted correctly across pods. I find the current MySQL pod which is running on lenovo, delete it and the replication controller restarts the pod again on dell.

I port-forward the new pod, reconnect MySQL workbench and it appears that the schema is intact. That means that NFS is able to persist the current data and move it between machines.

For interest, what happens if I restart the nfs-provisioner? This will be a good test to see how robust things are in a pretty significant failure.

$ kubectl get pods
NAME                                                     READY   STATUS    RESTARTS   AGE
mysql-64d7f649b-hpv8j                                    1/1     Running   0          14m
nfs-provisioner-78495f4f78-4qgcg                         1/1     Running   0          59m
weave-scope-agent-weave-scope-test-68mwl                 1/1     Running   0          21h
weave-scope-agent-weave-scope-test-f5m8h                 1/1     Running   0          21h
weave-scope-agent-weave-scope-test-mrjt8                 1/1     Running   0          21h
weave-scope-agent-weave-scope-test-mvptk                 1/1     Running   0          21h
weave-scope-agent-weave-scope-test-x9rgp                 1/1     Running   0          21h
weave-scope-agent-weave-scope-test-xzv6l                 1/1     Running   0          21h
weave-scope-frontend-weave-scope-test-78d78cf9fd-5ql92   1/1     Running   0          21h

$ kubectl delete pod/nfs-provisioner-78495f4f78-4qgcg
pod "nfs-provisioner-78495f4f78-4qgcg" deleted

Again, I redo the port-forward, open MySQL workbench and everything is still there. Nice! At this point I’m confident that dynamic NFS provisioning is working well.

The following links I found really helpful regarding setting up NFS:

— edit —

I didn’t test out the default storage class provisioning during this post, but see the post regarding setting up Jenkins in this series of posts as I tested it there and it works.

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