feat(zfspv): adding backup and restore support (#162)

This commit adds support for Backup and Restore controller, which will be watching for
the events. The velero plugin will create a Backup CR to create a backup
with the remote location information, the controller will send the data
to that remote location.

In the same way, the velero plugin will create a Restore CR to restore the
volume from the the remote location and the restore controller will restore
the data.

Steps to use velero plugin for ZFS-LocalPV are :

1. install velero

2. add openebs plugin

velero plugin add openebs/velero-plugin:latest

3. Create the volumesnapshot location :

for full backup :-

```yaml
apiVersion: velero.io/v1
kind: VolumeSnapshotLocation
metadata:
  name: default
  namespace: velero
spec:
  provider: openebs.io/zfspv-blockstore
  config:
    bucket: velero
    prefix: zfs
    namespace: openebs
    provider: aws
    region: minio
    s3ForcePathStyle: "true"
    s3Url: http://minio.velero.svc:9000
```

for incremental backup :-

```yaml
apiVersion: velero.io/v1
kind: VolumeSnapshotLocation
metadata:
  name: default
  namespace: velero
spec:
  provider: openebs.io/zfspv-blockstore
  config:
    bucket: velero
    prefix: zfs
    backup: incremental
    namespace: openebs
    provider: aws
    region: minio
    s3ForcePathStyle: "true"
    s3Url: http://minio.velero.svc:9000
```

4. Create backup

velero backup create my-backup --snapshot-volumes --include-namespaces=velero-ns --volume-snapshot-locations=aws-cloud-default --storage-location=default

5. Create Schedule

velero create schedule newschedule  --schedule="*/1 * * * *" --snapshot-volumes --include-namespaces=velero-ns --volume-snapshot-locations=aws-local-default --storage-location=default

6. Restore from backup

velero restore create --from-backup my-backup --restore-volumes=true --namespace-mappings velero-ns:ns1



Signed-off-by: Pawan <pawan@mayadata.io>

pkg/mgmt/backup/doc.go

@@ -0,0 +1,47 @@
+/*
+Copyright 2020 The OpenEBS Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/*
+The Backup flow is as follows:
+
+- plugin takes the backup of ZFSVolume CR so that it can be restored.
+
+- It will save the namespace information where the pvc is created also while taking the backup. Plugin will use this info if restoring without a namespace mapping to find if volume has already been restored.
+
+- plugin then creates the ZFSBackup CR with status as Init and with the destination volume and remote location where the data needs to be send.
+
+- Backup controller (on node) keeps a watch for new CRs associated with the node id. This node ID will be same as the Node ID present in the ZFSVolume resource.
+
+- if Backup status == init and not marked for deletion, the Backup controller will take a snapshot which needs to be send for the Backup purpose.
+
+- Backup controller will execute the `zfs send | remote-write` command which will send the data to the Backup server which is a server running by the plugin. The plugin will read the data and send that to remote location S3 or minio.
+
+- If Backup is deleted then corresponsing snapshot also gets deleted.
+
+
+Limitation :-
+
+- there should be enough space in the pool to accomodate the snapshot.
+
+- if there is a network error and backup failed and :
+    * Backup status update also failed, then backup will be retried from the beginning (TODO optimize it)
+    * Backup status update is successful, the Backup operation will fail.
+
+- A snapshot will exist as long as Backup is present and it will be cleaned up when the Backup is deleted.
+
+*/
+
+package backup