Volume Replication Operator

Overview

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.

Design

Volume Replication Operator follows controller pattern and provides extended APIs for storage disaster recovery. The extended APIs are provided via Custom Resource Definition (CRD).

VolumeReplicationClass

VolumeReplicationClass is a cluster scoped resource that contains driver related configuration parameters.

provisioner is name of the storage provisioner

parameters contains key-value pairs that are passed down to the driver. Users can add their own key-value pairs. Keys with replication.storage.openshift.io/ prefix are reserved by operator and not passed down to the driver.

Reserved parameter keys

• replication.storage.openshift.io/replication-secret-name
• replication.storage.openshift.io/replication-secret-namespace

apiVersion: replication.storage.openshift.io/v1alpha1
kind: VolumeReplicationClass
metadata:
  name: volumereplicationclass-sample
spec:
  provisioner: example.provisioner.io
  parameters:
    replication.storage.openshift.io/replication-secret-name: secret-name
    replication.storage.openshift.io/replication-secret-namespace: secret-namespace

VolumeReplication

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

volumeReplicationClass is the class providing replication

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

dataSource contains typed reference to the source being replicated.

• apiGroup is the group for the resource being referenced. If apiGroup is not specified, the specified Kind must be in the core API group. For any other third-party types, apiGroup is required.
• kind is the kind of resource being replicated. For eg. PersistentVolumeClaim
• name is the name of the resource

replicationHandle (optional) is an existing (but new) replication id

apiVersion: replication.storage.openshift.io/v1alpha1
kind: VolumeReplication
metadata:
  name: volumereplication-sample
  namespace: default
spec:
  volumeReplicationClass: volumereplicationclass-sample
  replicationState: primary
  replicationHandle: replicationHandle # optional
  dataSource:
    kind: PersistentVolumeClaim
    name: myPersistentVolumeClaim # should be in same namespace as VolumeReplication

Usage

Planned Storage Migration

Failover

In case of planned migration, 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.

On the Secondary Site, create VolumeReplication CR pointing to the same dataSource with replicationState as primary. When the operator sees this change, it will pass the information down to the driver via GRPC request to mark the dataSource as primary.

Failback

Once the planned work is done and you want to failback, update replicationState from primary to secondary in current Primary Site and secondary to primary in current Secondary Site after it is recovered. These changes are detected by operator and information is passed down to the driver via GRPC request.

Storage Disaster Recovery

Failover

In case of disaster recovery, create VolumeReplication CR at 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.

Failback

Once the failed cluster is recovered and you want to failback, update replicationState from primary to secondary in current Primary Site and secondary to primary in the recovered site. These changes are detected by operator and information is passed down to the driver via GRPC request to make the necessary changes.