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An Innovator’s Guide to Kubernetes Storage Using Ceph

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Kubernetes, the awesome container orchestration tool is changing the way applications are being developed and deployed. You can specify the required resources you want and have it available without worrying about the underlying infrastructure. Kubernetes is way ahead in terms of high availability, scaling, managing your application, but storage section in the k8s is still evolving. Many storage supports are getting added and are production ready.

People are preferring clustered applications to store the data. But, what about the non-clustered applications? Where does these applications store data to make it highly available? Considering these questions, let’s go through the Ceph storage and its integration with Kubernetes.

What is Ceph Storage?

Ceph is open source, software-defined storage maintained by RedHat. It’s capable of block, object, and file storage. The clusters of Ceph are designed in order to run on any hardware with the help of an algorithm called CRUSH (Controlled Replication Under Scalable Hashing). This algorithm ensures that all the data is properly distributed across the cluster and data quickly without any constraints. Replication, Thin provisioning, Snapshots are the key features of the Ceph storage.

There are good storage solutions like Gluster, Swift but we are going with Ceph for following reasons:

  1. File, Block, and Object storage in the same wrapper.
  2. Better transfer speed and lower latency
  3. Easily accessible storage that can quickly scale up or down

We are going to use 2 types of storage in this blog to integrate with kubernetes.

  1. Ceph-RBD
  2. CephFS

Ceph Deployment

Deploying highly available Ceph cluster is pretty straightforward and easy. I am assuming that you are familiar with setting up the Ceph cluster. If not then refer the official document here.

If you check the status, you should see something like:

# ceph -s
  cluster:
    id:     ed0bfe4e-f44c-4797-9bc6-21a988b645c7
    health: HEALTH_OK
 
  services:
    mon: 3 daemons, quorum ip-10-0-1-118,ip-10-0-1-172,ip-10-0-1-227
    mgr: ip-10-0-1-118(active), standbys: ip-10-0-1-227, ip-10-0-1-172
    mds: cephfs-1/1/1 up  {0=ip-10-0-1-118=up:active}
    osd: 3 osds: 3 up, 3 in
 
  data:
    pools:   2 pools, 160 pgs
    objects: 22  objects, 19 KiB
    usage:   3.0 GiB used, 21 GiB / 24 GiB avail
    pgs:     160 active+clean
@velotiotech

Here notice that my Ceph monitors IPs are 10.0.1.118, 10.0.1.227 and 10.0.1.172

K8s Integration

After setting up the Ceph cluster, we would consume it with Kubernetes.  I am assuming that your Kubernetes cluster is up and running. We will be using Ceph-RBD and CephFS as storage in Kubernetes.

Ceph-RBD and Kubernetes

We need a Ceph RBD client to achieve interaction between Kubernetes cluster and CephFS. This client is not in the official kube-controller-manager container so let’s try to create the external storage plugin for Ceph.

kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: rbd-provisioner
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"]
    resourceNames: ["kube-dns","coredns"]
    verbs: ["list", "get"]
  - apiGroups: [""]
    resources: ["endpoints"]
    verbs: ["get", "list", "watch", "create", "update", "patch"]
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: rbd-provisioner
subjects:
  - kind: ServiceAccount
    name: rbd-provisioner
    namespace: kube-system
roleRef:
  kind: ClusterRole
  name: rbd-provisioner
  apiGroup: rbac.authorization.k8s.io
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: Role
metadata:
  name: rbd-provisioner
rules:
- apiGroups: [""]
  resources: ["secrets"]
  verbs: ["get"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: rbd-provisioner
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: rbd-provisioner
subjects:
- kind: ServiceAccount
  name: rbd-provisioner
  namespace: kube-system
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: rbd-provisioner
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: rbd-provisioner
spec:
  replicas: 1
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: rbd-provisioner
    spec:
      containers:
      - name: rbd-provisioner
        image: "quay.io/external_storage/rbd-provisioner:latest"
        env:
        - name: PROVISIONER_NAME
          value: ceph.com/rbd
      serviceAccount: rbd-provisioner

# kubectl create -n kube-system -f  Ceph-RBD-Provisioner.yaml

  • You will get output like this:
clusterrole.rbac.authorization.k8s.io/rbd-provisioner created
clusterrolebinding.rbac.authorization.k8s.io/rbd-provisioner created
role.rbac.authorization.k8s.io/rbd-provisioner created
rolebinding.rbac.authorization.k8s.io/rbd-provisioner created
serviceaccount/rbd-provisioner created
deployment.extensions/rbd-provisioner created

  • Check RBD volume provisioner status and wait till it comes up in running state. You would see something like following:
[root@ip-10-0-1-226 Ceph-RBD]# kubectl get pods -l app=rbd-provisioner -n kube-system
NAME                               READY     STATUS    RESTARTS   AGE
rbd-provisioner-857866b5b7-vc4pr   1/1       Running   0          16s

  • Once the provisioner is up, provisioner needs the admin key for the storage provision. You can run the following command to get the admin key:
# ceph auth get-key client.admin
AQDyWw9dOUm/FhAA4JCA9PXkPo6+OXpOj9N2ZQ==

# kubectl create secret generic ceph-secret 
    --type="kubernetes.io/rbd" 
    --from-literal=key='AQDyWw9dOUm/FhAA4JCA9PXkPo6+OXpOj9N2ZQ==' 
    --namespace=kube-system

  • Let’s create a separate Ceph pool for Kubernetes and the new client key:
# ceph --cluster ceph osd pool create kube 1024 1024
# ceph --cluster ceph auth get-or-create client.kube mon 'allow r' osd 'allow rwx pool=kube'

  • Get the auth token which we created in the above command and create kubernetes secret for new client secret for kube pool.
# ceph --cluster ceph auth get-key client.kube
AQDabg9d4MBeIBAAaOhTjqsYpsNa4X10V0qCfw==

# kubectl create secret generic ceph-secret-kube 
    --type="kubernetes.io/rbd" 
    --from-literal=key=”AQDabg9d4MBeIBAAaOhTjqsYpsNa4X10V0qCfw=='' 
    --namespace=kube-system

  • Now let’s create the storage class.
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast-rbd
provisioner: ceph.com/rbd
parameters:
  monitors: 10.0.1.118:6789, 10.0.1.227:6789, 10.0.1.172:6789
  adminId: admin
  adminSecretName: ceph-secret
  adminSecretNamespace: kube-system
  pool: kube
  userId: kube
  userSecretName: ceph-secret-kube
  userSecretNamespace: kube-system
  imageFormat: "2"
  imageFeatures: layering

# kubectl create -f Ceph-RBD-StorageClass.yaml

  • We are all set now. We can test the Ceph-RBD by creating the PVC. After creating the PVC, PV will get created automatically.  Let’s create the PVC now:
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: testclaim
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
  storageClassName: fast-rbd

# kubectl create -f Ceph-RBD-PVC.yaml

[root@ip-10-0-1-226 Ceph-RBD]# kubectl get pvc
NAME      STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
testclaim  Bound     pvc-c215ad98-95b3-11e9-8b5d-12e154d66096   1Gi        RWO            fast-rbd       2m

  • If you check pvc, you’ll find it shows that it’s been bounded with the pv which got created by storage class.
  • Let’s check the persistent volume
[root@ip-10-0-1-226 Ceph-RBD]# kubectl get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM             STORAGECLASS   REASON    AGE
pvc-c215ad98-95b3-11e9-8b5d-12e154d66096   1Gi        RWO            Delete           Bound     default/testclaim   fast-rbd                 8m

Till now we have seen how to use the block based storage i.e Ceph-RBD with kubernetes by creating the dynamic storage provisioner. Now let’s go through the process for setting up the storage using file system based storage i.e. CephFS.  

CephFS and Kubernetes

  • Let’s create the provisioner and storage class for the CephFS.  Create the dedicated namespace for CephFS
# kubectl create ns cephfs

  • Create the kubernetes secrete using the Ceph admin auth token
# ceph auth get-key client.admin
AQDyWw9dOUm/FhAA4JCA9PXkPo6+OXpOj9N2ZQ==

# kubectl create secret generic ceph-secret-admin --from-literal=key="AQDyWw9dOUm/FhAA4JCA9PXkPo6+OXpOj9N2ZQ==" -n cephfs

  • Create the cluster role, role binding, provisioner
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: cephfs-provisioner
  namespace: cephfs
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"]
    resourceNames: ["kube-dns","coredns"]
    verbs: ["list", "get"]
---
kind: ClusterRoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: cephfs-provisioner
subjects:
  - kind: ServiceAccount
    name: cephfs-provisioner
    namespace: cephfs
roleRef:
  kind: ClusterRole
  name: cephfs-provisioner
  apiGroup: rbac.authorization.k8s.io
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: cephfs-provisioner
  namespace: cephfs
rules:
  - apiGroups: [""]
    resources: ["secrets"]
    verbs: ["create", "get", "delete"]
  - apiGroups: [""]
    resources: ["endpoints"]
    verbs: ["get", "list", "watch", "create", "update", "patch"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: cephfs-provisioner
  namespace: cephfs
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: cephfs-provisioner
subjects:
- kind: ServiceAccount
  name: cephfs-provisioner
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: cephfs-provisioner
  namespace: cephfs
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: cephfs-provisioner
  namespace: cephfs
spec:
  replicas: 1
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: cephfs-provisioner
    spec:
      containers:
      - name: cephfs-provisioner
        image: "quay.io/external_storage/cephfs-provisioner:latest"
        env:
        - name: PROVISIONER_NAME
          value: ceph.com/cephfs
        - name: PROVISIONER_SECRET_NAMESPACE
          value: cephfs
        command:
        - "/usr/local/bin/cephfs-provisioner"
        args:
        - "-id=cephfs-provisioner-1"
      serviceAccount: cephfs-provisioner

# kubectl create -n cephfs -f Ceph-FS-Provisioner.yaml

  • Create the storage class
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: cephfs
provisioner: ceph.com/cephfs
parameters:
    monitors: 10.0.1.226:6789, 10.0.1.205:6789, 10.0.1.82:6789
    adminId: admin
    adminSecretName: ceph-secret-admin
    adminSecretNamespace: cephfs
    claimRoot: /pvc-volumes

# kubectl create -f Ceph-FS-StorageClass.yaml

  • We are all set now. CephFS provisioner is created. Let’s wait till it gets into running state.
# kubectl get pods -n cephfs
NAME                                 READY     STATUS    RESTARTS   AGE
cephfs-provisioner-8d957f95f-s7mdq   1/1       Running   0          1m

  • Once the CephFS provider is up, try creating the persistent volume claim. In this step, storage class will take care of creating the persistent volume dynamically.
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: claim1
spec:
  storageClassName: cephfs
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 1Gi

# kubectl create -f Ceph-FS-PVC.yaml

  • Let’s check the create PV and PVC
# kubectl get pvc
NAME      STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
claim1    Bound     pvc-a7db18a7-9641-11e9-ab86-12e154d66096   1Gi        RWX            cephfs         2m

# kubectl get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM            STORAGECLASS   REASON    AGE
pvc-a7db18a7-9641-11e9-ab86-12e154d66096   1Gi        RWX            Delete           Bound     default/claim1   cephfs                   2m

Conclusion

We have seen how to integrate the Ceph storage with Kubernetes. In the integration, we covered ceph-rbd and cephfs. This approach is highly useful when your application is not clustered application and if you are looking to make it highly available.

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