RBD Mirroring

Disaster Recovery¶

Disaster recovery (DR) is an organization's ability to react to and recover from an incident that negatively affects business operations. This plan comprises strategies for minimizing the consequences of a disaster, so an organization can continue to operate – or quickly resume the key operations. Thus, disaster recovery is one of the aspects of business continuity. One of the solutions, to achieve the same, is RBD mirroring.

RBD Mirroring¶

RBD mirroring is an asynchronous replication of RBD images between multiple Ceph clusters. This capability is available in two modes:

• Journal-based: Every write to the RBD image is first recorded to the associated journal before modifying the actual image. The remote cluster will read from this associated journal and replay the updates to its local image.
• Snapshot-based: This mode uses periodically scheduled or manually created RBD image mirror-snapshots to replicate crash-consistent RBD images between clusters.

Create RBD Pools¶

In this section, we create specific RBD pools that are RBD mirroring enabled for use with the DR use case.

Execute the following steps on each peer cluster to create mirror enabled pools:

• Create a RBD pool that is enabled for mirroring by adding the section spec.mirroring in the CephBlockPool CR:

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apiVersion: ceph.rook.io/v1
kind: CephBlockPool
metadata:
  name: mirroredpool
  namespace: rook-ceph
spec:
  replicated:
    size: 1
  mirroring:
    enabled: true
    mode: image

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kubectl create -f pool-mirrored.yaml

• Repeat the steps on the peer cluster.

See the CephBlockPool documentation for more details.

Bootstrap Peers¶

In order for the rbd-mirror daemon to discover its peer cluster, the peer must be registered and a user account must be created.

The following steps enable bootstrapping peers to discover and authenticate to each other:

• For Bootstrapping a peer cluster its bootstrap secret is required. To determine the name of the secret that contains the bootstrap secret execute the following command on the remote cluster (cluster-2)

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[cluster-2]$ kubectl get cephblockpool.ceph.rook.io/mirroredpool -n rook-ceph -ojsonpath='{.status.info.rbdMirrorBootstrapPeerSecretName}'

Here, pool-peer-token-mirroredpool is the desired bootstrap secret name.

• The secret pool-peer-token-mirroredpool contains all the information related to the token and needs to be injected to the peer, to fetch the decoded secret:

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[cluster-2]$ kubectl get secret -n rook-ceph pool-peer-token-mirroredpool -o jsonpath='{.data.token}'|base64 -d
eyJmc2lkIjoiNGQ1YmNiNDAtNDY3YS00OWVkLThjMGEtOWVhOGJkNDY2OTE3IiwiY2xpZW50X2lkIjoicmJkLW1pcnJvci1wZWVyIiwia2V5IjoiQVFDZ3hmZGdxN013R0JBQWZzcUtCaGpZVjJUZDRxVzJYQm5kemc9PSIsIm1vbl9ob3N0IjoiW3YyOjE5Mi4xNjguMzkuMzY6MzMwMCx2MToxOTIuMTY4LjM5LjM2OjY3ODldIn0=

• With this Decoded value, create a secret on the primary site (cluster-1):

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[cluster-1]$ kubectl -n rook-ceph create secret generic rbd-primary-site-secret --from-literal=token=eyJmc2lkIjoiNGQ1YmNiNDAtNDY3YS00OWVkLThjMGEtOWVhOGJkNDY2OTE3IiwiY2xpZW50X2lkIjoicmJkLW1pcnJvci1wZWVyIiwia2V5IjoiQVFDZ3hmZGdxN013R0JBQWZzcUtCaGpZVjJUZDRxVzJYQm5kemc9PSIsIm1vbl9ob3N0IjoiW3YyOjE5Mi4xNjguMzkuMzY6MzMwMCx2MToxOTIuMTY4LjM5LjM2OjY3ODldIn0= --from-literal=pool=mirroredpool

• This completes the bootstrap process for cluster-1 to be peered with cluster-2.
• Repeat the process switching cluster-2 in place of cluster-1, to complete the bootstrap process across both peer clusters.

For more details, refer to the official rbd mirror documentation on how to create a bootstrap peer.

Configure the RBDMirror Daemon¶

Replication is handled by the rbd-mirror daemon. The rbd-mirror daemon is responsible for pulling image updates from the remote, peer cluster, and applying them to image within the local cluster.

Creation of the rbd-mirror daemon(s) is done through the custom resource definitions (CRDs), as follows:

• Create mirror.yaml, to deploy the rbd-mirror daemon

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apiVersion: ceph.rook.io/v1
kind: CephRBDMirror
metadata:
  name: my-rbd-mirror
  namespace: openshift-storage
spec:
  # the number of rbd-mirror daemons to deploy
  count: 1

• Create the RBD mirror daemon

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[cluster-1]$ kubectl create -f mirror.yaml -n rook-ceph

• Validate if rbd-mirror daemon pod is now up

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[cluster-1]$ kubectl get pods -n rook-ceph
rook-ceph-rbd-mirror-a-6985b47c8c-dpv4k  1/1  Running  0  10s

• Verify that daemon health is OK

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kubectl get cephblockpools.ceph.rook.io mirroredpool -n rook-ceph -o jsonpath='{.status.mirroringStatus.summary}'
{"daemon_health":"OK","health":"OK","image_health":"OK","states":{"replaying":1}}

• Repeat the above steps on the peer cluster.

See the CephRBDMirror CRD for more details on the mirroring settings.

Add mirroring peer information to RBD pools¶

Each pool can have its own peer. To add the peer information, patch the already created mirroring enabled pool to update the CephBlockPool CRD.

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[cluster-1]$ kubectl -n rook-ceph patch cephblockpool mirroredpool --type merge -p '{"spec":{"mirroring":{"peers": {"secretNames": ["rbd-primary-site-secret"]}}}}'

Create VolumeReplication CRDs¶

Volume Replication Operator follows controller pattern and provides extended APIs for storage disaster recovery. The extended APIs are provided via Custom Resource Definition(CRD). Create the VolumeReplication CRDs on all the peer clusters.

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kubectl create -f https://raw.githubusercontent.com/csi-addons/volume-replication-operator/v0.3.0/config/crd/bases/replication.storage.openshift.io_volumereplications.yaml
kubectl create -f https://raw.githubusercontent.com/csi-addons/volume-replication-operator/v0.3.0/config/crd/bases/replication.storage.openshift.io_volumereplicationclasses.yaml

Enable CSI Replication Sidecars¶

To achieve RBD Mirroring, csi-omap-generator and volume-replication containers need to be deployed in the RBD provisioner pods, which are not enabled by default.

• Omap Generator: Omap generator is a sidecar container that when deployed with the CSI provisioner pod, generates the internal CSI omaps between the PV and the RBD image. This is required as static PVs are transferred across peer clusters in the DR use case, and hence is needed to preserve PVC to storage mappings.

• Volume Replication Operator: Volume Replication Operator is a kubernetes operator that provides common and reusable APIs for storage disaster recovery. It is based on csi-addons/spec specification and can be used by any storage provider. For more details, refer to volume replication operator.

Execute the following steps on each peer cluster to enable the OMap generator and Volume Replication sidecars:

• Edit the rook-ceph-operator-config configmap and add the following configurations

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kubectl edit cm rook-ceph-operator-config -n rook-ceph

Add the following properties if not present:

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data:
  CSI_ENABLE_OMAP_GENERATOR: "true"
  CSI_ENABLE_VOLUME_REPLICATION: "true"

• After updating the configmap with those settings, two new sidecars should now start automatically in the CSI provisioner pod.
• Repeat the steps on the peer cluster.

Volume Replication Custom Resources¶

VolumeReplication CRDs provide support for two custom resources:

• VolumeReplicationClass: VolumeReplicationClass is a cluster scoped resource that contains driver related configuration parameters. It holds the storage admin information required for the volume replication operator.

• VolumeReplication: VolumeReplication is a namespaced resource that contains references to storage object to be replicated and VolumeReplicationClass corresponding to the driver providing replication.

Enable mirroring on a PVC¶

Below guide assumes that we have a PVC (rbd-pvc) in BOUND state; created using StorageClass with Retain reclaimPolicy.

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[cluster-1]$ kubectl get pvc
NAME      STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS      AGE
rbd-pvc   Bound    pvc-65dc0aac-5e15-4474-90f4-7a3532c621ec   1Gi        RWO            csi-rbd-sc   44s

Create a Volume Replication Class CR¶

In this case, we create a Volume Replication Class on cluster-1

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[cluster-1]$ kubectl apply -f deploy/examples/volume-replication-class.yaml

Create a VolumeReplication CR¶

• Once VolumeReplicationClass is created, create a Volume Replication for the PVC which we intend to replicate to secondary cluster.

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[cluster-1]$ kubectl apply -f deploy/examples/volume-replication.yaml

Checking Replication Status¶

replicationState is the state of the volume being referenced. Possible values are primary, secondary, and resync.

• primary denotes that the volume is primary.
• secondary denotes that the volume is secondary.
• resync denotes that the volume needs to be resynced.

To check VolumeReplication CR status:

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[cluster-1]$kubectl get volumereplication pvc-volumereplication -oyaml

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...
spec:
  dataSource:
    apiGroup: ""
    kind: PersistentVolumeClaim
    name: rbd-pvc
  replicationState: primary
  volumeReplicationClass: rbd-volumereplicationclass
status:
  conditions:
  - lastTransitionTime: "2021-05-04T07:39:00Z"
    message: ""
    observedGeneration: 1
    reason: Promoted
    status: "True"
    type: Completed
  - lastTransitionTime: "2021-05-04T07:39:00Z"
    message: ""
    observedGeneration: 1
    reason: Healthy
    status: "False"
    type: Degraded
  - lastTransitionTime: "2021-05-04T07:39:00Z"
    message: ""
    observedGeneration: 1
    reason: NotResyncing
    status: "False"
    type: Resyncing
  lastCompletionTime: "2021-05-04T07:39:00Z"
  lastStartTime: "2021-05-04T07:38:59Z"
  message: volume is marked primary
  observedGeneration: 1
  state: Primary

Backup & Restore¶

Here, we take a backup of PVC and PV object on one site, so that they can be restored later to the peer cluster.

Take backup on cluster-1¶

• Take backup of the PVC rbd-pvc

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[cluster-1]$ kubectl  get pvc rbd-pvc -oyaml > pvc-backup.yaml

• Take a backup of the PV, corresponding to the PVC

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[cluster-1]$ kubectl get pv/pvc-65dc0aac-5e15-4474-90f4-7a3532c621ec -oyaml > pv_backup.yaml

Restore the backup on cluster-2¶

• Create storageclass on the secondary cluster

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[cluster-2]$ kubectl create -f deploy/examples/csi/rbd/storageclass.yaml

• Create VolumeReplicationClass on the secondary cluster

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[cluster-1]$ kubectl apply -f deploy/examples/volume-replication-class.yaml
volumereplicationclass.replication.storage.openshift.io/rbd-volumereplicationclass created

• If Persistent Volumes and Claims are created manually on the secondary cluster, remove the claimRef on the backed up PV objects in yaml files; so that the PV can get bound to the new claim on the secondary cluster.

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...
spec:
  accessModes:
  - ReadWriteOnce
  capacity:
    storage: 1Gi
  claimRef:
    apiVersion: v1
    kind: PersistentVolumeClaim
    name: rbd-pvc
    namespace: default
    resourceVersion: "64252"
    uid: 65dc0aac-5e15-4474-90f4-7a3532c621ec
  csi:
...

• Apply the Persistent Volume backup from the primary cluster

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[cluster-2]$ kubectl create -f pv-backup.yaml

• Apply the Persistent Volume claim from the restored backup

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[cluster-2]$ kubectl create -f pvc-backup.yaml

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[cluster-2]$ kubectl get pvc
NAME      STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS      AGE
rbd-pvc   Bound    pvc-65dc0aac-5e15-4474-90f4-7a3532c621ec   1Gi        RWO            rook-ceph-block   44s