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doc: Add documentation for DR

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Add documenation for Disaster Recovery
which steps to Failover and Failback in case
of a planned migration or a Disaster.

Signed-off-by: Yug Gupta <yuggupta27@gmail.com>
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# Failover and Failback In Disaster Recovery
[RBD mirroring](https://docs.ceph.com/en/latest/rbd/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.
This documentation assumes that `rbd mirroring` is set up between
two clusters.
For more information on how to set up rbd mirroring, refer to
[ceph documentation](https://docs.ceph.com/en/latest/rbd/rbd-mirroring/).
## Deploy the Volume Replication CRD
Volume Replication Operator is a kubernetes operator that provides common
and reusable APIs for storage disaster recovery.
It is based on [csi-addons/spec](https://github.com/csi-addons/spec)
specification and can be used by any storage provider.
Volume Replication Operator follows controller pattern and provides
extended APIs for storage disaster recovery.
The extended APIs are provided via Custom Resource Definition (CRD).
>:bulb: For more information, please refer to the
> [volume-replication-operator](https://github.com/csi-addons/volume-replication-operator).
* Deploy the `VolumeReplicationClass` CRD
```bash
kubectl create -f https://raw.githubusercontent.com/csi-addons/volume-replication-operator/release-v0.1/config/crd/bases/replication.storage.openshift.io_volumereplicationclasses.yaml
customresourcedefinition.apiextensions.k8s.io/volumereplicationclasses.replication.storage.openshift.io created
```
* Deploy the `VolumeReplication` CRD
```bash
kubectl create -f https://raw.githubusercontent.com/csi-addons/volume-replication-operator/release-v0.1/config/crd/bases/replication.storage.openshift.io_volumereplications.yaml
customresourcedefinition.apiextensions.k8s.io/volumereplications.replication.storage.openshift.io created created
```
The VolumeReplicationClass and VolumeReplication CRDs are now created.
>:bulb: **Note:** Use the latest available release for Volume Replication Operator.
> See [releases](https://github.com/csi-addons/volume-replication-operator/branches)
> for more information.
### Add RBAC rules for Volume Replication Operator
Add the below mentioned rules to `rbd-external-provisioner-runner`
ClusterRole in [csi-provisioner-rbac.yaml](https://github.com/ceph/ceph-csi/blob/release-v3.3/deploy/rbd/kubernetes/csi-provisioner-rbac.yaml)
```yaml
- apiGroups: ["replication.storage.openshift.io"]
resources: ["volumereplications", "volumereplicationclasses"]
verbs: ["create", "delete", "get", "list", "patch", "update", "watch"]
- apiGroups: ["replication.storage.openshift.io"]
resources: ["volumereplications/finalizers"]
verbs: ["update"]
- apiGroups: ["replication.storage.openshift.io"]
resources: ["volumereplications/status"]
verbs: ["get", "patch", "update"]
- apiGroups: ["replication.storage.openshift.io"]
resources: ["volumereplicationclasses/status"]
verbs: ["get"]
```
### Deploy the Volume Replication Sidecar
To deploy `volume-replication` sidecar container in `csi-rbdplugin-provisioner`
pod, add the following yaml to
[csi-rbdplugin-provisioner deployment](https://github.com/ceph/ceph-csi/blob/release-v3.3/deploy/rbd/kubernetes/csi-rbdplugin-provisioner.yaml).
```yaml
- name: volume-replication
image: quay.io/csiaddons/volumereplication-operator:v0.1.0
args :
- "--metrics-bind-address=0"
- "--leader-election-namespace=$(NAMESPACE)"
- "--driver-name=rbd.csi.ceph.com"
- "--csi-address=$(ADDRESS)"
- "--rpc-timeout=150s"
- "--health-probe-bind-address=:9998"
- "--leader-elect=true"
env:
- name: ADDRESS
value: unix:///csi/csi-provisioner.sock
- name: NAMESPACE
valueFrom:
fieldRef:
fieldPath: metadata.namespace
imagePullPolicy: "IfNotPresent"
volumeMounts:
- name: socket-dir
mountPath: /csi
```
## VolumeReplicationClass and VolumeReplication
### 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.
>:bulb: For more information, please refer to the
> [volume-replication-operator](https://github.com/csi-addons/volume-replication-operator).
Let's say we have a *PVC* (rbd-pvc) in BOUND state; created using
*StorageClass* with `Retain` reclaimPolicy.
```bash
kubectl get pvc --context=cluster-1
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
rbd-pvc Bound pvc-65dc0aac-5e15-4474-90f4-7a3532c621ec 1Gi RWO csi-rbd-sc 44s
```
* Create Volume Replication Class on cluster-1
```yaml
$cat <<EOF | kubectl --context=cluster1 apply -f -
apiVersion: replication.storage.openshift.io/v1alpha1
kind: VolumeReplicationClass
metadata:
name: rbd-volumereplicationclass
spec:
provisioner: rbd.csi.ceph.com
parameters:
mirroringMode: snapshot
schedulingInterval: "12m"
schedulingStartTime: "16:18:43"
replication.storage.openshift.io/replication-secret-name: csi-rbd-secret
replication.storage.openshift.io/replication-secret-namespace: default
EOF
```
>:bulb: **Note:** The `schedulingInterval` can be specified in formats of
> minutes, hours or days using suffix `m`,`h` and `d` respectively.
> The optional schedulingStartTime can be specified using the ISO 8601
> time format.
* Once VolumeReplicationClass is created,create a Volume Replication for
the PVC which we intend to replicate to secondary cluster.
```yaml
$cat <<EOF | kubectl --context=cluster-1 apply -f -
apiVersion: replication.storage.openshift.io/v1alpha1
kind: VolumeReplication
metadata:
name: pvc-volumereplication
spec:
volumeReplicationClass: rbd-volumereplicationclass
replicationState: primary
dataSource:
apiGroup: ""
kind: PersistentVolumeClaim
name: rbd-pvc # Name of the PVC to which mirroring to be enabled.
EOF
```
>:memo: *VolumeReplication* is a namespace scoped object. Thus,
> it should be created in the same namespace as of PVC.
`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:
```yaml
kubectl get volumereplication pvc-volumereplication --context=cluster-1 -oyaml
...
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
```
* Take a backup of PVC and PV object on primary cluster(cluster-1)
* Take backup of the PVC `rbd-pvc`
```bash
kubectl get pvc rbd-pvc -oyaml >pvc-backup.yaml
```
* Take a backup of the PV, corresponding to the PVC
```bash
kubectl get pv/pvc-65dc0aac-5e15-4474-90f4-7a3532c621ec -oyaml >pv_backup.yaml
```
>:bulb: We can also take backup using external tools like **Velero**.
> Refer [velero documentation]((https://velero.io/docs/main/)) for more information.
* Restoring on the secondary cluster(cluster-2)
* Create storageclass on the secondary cluster
```bash
kubectl create -f examples/rbd/storageclass.yaml --context=cluster-2
storageclass.storage.k8s.io/csi-rbd-sc created
```
* Create VolumeReplicationClass on the secondary cluster
```bash
cat <<EOF | kubectl --context=cluster-2 apply -f -
apiVersion: replication.storage.openshift.io/v1alpha1
kind: VolumeReplicationClass
metadata:
name: rbd-volumereplicationclass
spec:
provisioner: rbd.csi.ceph.com
parameters:
mirroringMode: snapshot
replication.storage.openshift.io/replication-secret-name: csi-rbd-secret
replication.storage.openshift.io/replication-secret-namespace: default
EOF
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.
```yaml
...
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
```bash
kubectl create -f pv-backup.yaml --context=cluster-2
persistentvolume/pvc-65dc0aac-5e15-4474-90f4-7a3532c621ec created
```
* Apply the Persistent Volume claim from the restored backup
```bash
kubectl create -f pvc-backup.yaml --context=cluster-2
persistentvolumeclaim/rbd-pvc created
```
```bash
kubectl get pvc --context=cluster-2
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
rbd-pvc Bound pvc-65dc0aac-5e15-4474-90f4-7a3532c621ec 1Gi RWO csi-rbd-sc 44s
```
## Planned Migration
> Use cases: Datacenter maintenance, Technology refresh, Disaster avoidance, etc.
### Failover
The failover operation is the process of switching production to a
backup facility (normally your recovery site). In the case of Failover,
access to the image on the primary site should be stopped.
The image should now be made *primary* on the secondary cluster so that
the access can be resumed there.
:memo: As mentioned in the pre-requisites, periodic or one time backup of
the application should be available for restore on the secondary site (cluster-b).
Follow the below steps for planned migration of workload from primary
cluster to secondary cluster:
* Scale down all the application pods which are using the
mirrored PVC on the Primary Cluster
* Take a back up of PVC and PV object from the primary cluster.
This can be done using some backup tools like
[velero](https://velero.io/docs/main/).
* Update `replicationState` to `secondary` in VolumeReplication CR at Primary Site.
When the operator sees this change, it will pass the information down to the
driver via GRPC request to mark the dataSource as `secondary`.
* If you are manually recreating the PVC and PV on the secondary cluster,
remove the `claimRef` section in the PV objects.
* Recreate the storageclass, PVC, and PV objects on the secondary site.
* As you are creating the static binding between PVC and PV, a new PV won’t
be created here, the PVC will get bind to the existing PV.
* Create the VolumeReplicationClass on the secondary site.
* Create the VolumeReplications for all the PVC’s for which mirroring
is enabled
* `replicationState` should be `primary` for all the PVC’s on
the secondary site.
* Check whether the image is marked `primary` on the secondary site
by verifying it in VolumeReplication CR status.
* Once the Image is marked as `primary`, the PVC is now ready
to be used. Now, we can scale up the applications to use the PVC.
>:memo: **WARNING**: In Async Disaster recovery use case, we don't
> get the complete data. We will only get the crash-consistent data
> based on the snapshot interval time.
### Failback
To perform a failback operation to primary cluster in case of planned migration
, just repeat the Failback steps in vice-versa.
>:memo: **Remember**: We can skip the backup-restore operations
> in case of failback if the required yamls are already present on
> the primary cluster. Any new PVCs will still need to be restored on the
> primary site.
## Disaster Recovery
> Use cases: Natural disasters, Power failures, System failures, and crashes, etc.
### Failover (abrupt shutdown)
In case of Disaster recovery, create VolumeReplication CR at the Secondary Site.
Since the connection to the Primary Site is lost, the operator automatically
sends a GRPC request down to the driver to forcefully mark the dataSource as `primary`.
* If you are manually creating the PVC and PV on the secondary cluster, remove
the claimRef section in the PV objects.
* Create the storageclass, PVC, and PV objects on the secondary site.
* As you are creating the static binding between PVC and PV, a new PV won’t be
created here, the PVC will get bind to the existing PV.
* Create the VolumeReplicationClass and VolumeReplication CR on the secondary site.
* Check whether the image is `primary` on secondary site, by verifying in
the VolumeReplication CR status.
* Once the Image is marked as `primary`, the PVC is now ready to be used. Now,
we can scale up the applications to use the PVC.
### Failback (post-disaster recovery)
Once the failed cluster is recovered on the primary site and you want to failback
from secondary site, follow the below steps:
* Update the VolumeReplication CR replicationState
from `primary` to `secondary` on the primary site.
* Scale down the applications on the secondary site.
* Update the VolumeReplication CR replicationState from `primary` to
`secondary` in secondary site.
* On the primary site, verify that the VolumeReplication status is marked as
volume ready to use
* Once the volume is marked to ready to use, change the replicationState state
from `secondary` to `primary` in primary site.
* Scale up the applications again on the primary site.