Add warnings about snapshot consistency

We supported creating snapshots, but not doing anything with them. This
removes the manual task of restoring a snapshot and replace it with a
PVC abstraction of rolling back to a snapshot.

While Ceph recommends cloning a snapshot instead of rolling back, due to
the time taken, in our usecase I don't think that is an optimal
strategy, as it will leave dangling clones that we'd then have to
manage.

Closes #183

api-daemon/pvcapid/flaskapi.py

@@ -6362,6 +6362,59 @@ api.add_resource(
 )
 
 
+# /storage/ceph/snapshot/<pool>/<volume>/<snapshot>/rollback
+class API_Storage_Ceph_Snapshot_Rollback_Element(Resource):
+    @Authenticator
+    def post(self, pool, volume, snapshot):
+        """
+        Roll back an RBD volume {volume} in pool {pool} to snapshot {snapshot}
+
+        WARNING: This action cannot be done on an active RBD volume. All IO MUST be stopped first.
+        ---
+        tags:
+          - storage / ceph
+        parameters:
+          - in: query
+            name: snapshot
+            type: string
+            required: true
+            description: The name of the snapshot
+          - in: query
+            name: volume
+            type: string
+            required: true
+            description: The name of the volume
+          - in: query
+            name: pool
+            type: integer
+            required: true
+            description: The name of the pool
+        responses:
+          200:
+            description: OK
+            schema:
+              type: object
+              id: Message
+          404:
+            description: Not found
+            schema:
+              type: object
+              id: Message
+          400:
+            description: Bad request
+            schema:
+              type: object
+              id: Message
+        """
+        return api_helper.ceph_volume_snapshot_rollback(pool, volume, snapshot)
+
+
+api.add_resource(
+    API_Storage_Ceph_Snapshot_Rollback_Element,
+    "/storage/ceph/snapshot/<pool>/<volume>/<snapshot>/rollback",
+)
+
+
 ##########################################################
 # Provisioner API
 ##########################################################

api-daemon/pvcapid/helper.py

@@ -2183,6 +2183,22 @@ def ceph_volume_snapshot_rename(zkhandler, pool, volume, name, new_name):
     return output, retcode
 
 
+@ZKConnection(config)
+def ceph_volume_snapshot_rollback(zkhandler, pool, volume, name):
+    """
+    Roll back a Ceph RBD volume to a given snapshot in the PVC Ceph storage cluster.
+    """
+    retflag, retdata = pvc_ceph.rollback_snapshot(zkhandler, pool, volume, name)
+
+    if retflag:
+        retcode = 200
+    else:
+        retcode = 400
+
+    output = {"message": retdata.replace('"', "'")}
+    return output, retcode
+
+
 @ZKConnection(config)
 def ceph_volume_snapshot_remove(zkhandler, pool, volume, name):
     """

client-cli/pvc/cli/cli.py

@@ -4325,6 +4325,10 @@ def cli_storage_volume_snapshot():
 def cli_storage_volume_snapshot_add(pool, volume, name):
     """
     Add a snapshot with name NAME of Ceph RBD volume VOLUME in pool POOL.
+
+    WARNING: RBD snapshots are crash-consistent but not filesystem-aware. If a snapshot was taken
+    of a running VM, restoring that snapshot will be equivalent to having forcibly restarted the
+    VM at the moment of the snapshot.
     """
 
     retcode, retmsg = pvc.lib.storage.ceph_snapshot_add(CLI_CONFIG, pool, volume, name)
@@ -4372,6 +4376,36 @@ def cli_storage_volume_snapshot_remove(pool, volume, name):
     finish(retcode, retmsg)
 
 
+###############################################################################
+# > pvc storage volume snapshot rollback
+###############################################################################
+@click.command(name="rollback", short_help="Roll back RBD volume to snapshot.")
+@connection_req
+@click.argument("pool")
+@click.argument("volume")
+@click.argument("name")
+@confirm_opt("Roll back to snapshot {name} for volume {pool}/{volume}")
+def cli_storage_volume_snapshot_rollback(pool, volume, name):
+    """
+    Roll back the Ceph RBD volume VOLUME in pool POOL to the snapshot NAME.
+
+    DANGER: All data written to the volume since the given snapshot will be permanently lost.
+
+    WARNING: A rollback cannot be performed on an RBD volume with active I/O. Doing so will cause
+    undefined behaviour and possible corruption. Ensure that any VM(s) using this RBD volume are
+    stopped or disabled before attempting a snapshot rollback.
+
+    WARNING: RBD snapshots are crash-consistent but not filesystem-aware. If a snapshot was taken
+    of a running VM, restoring that snapshot will be equivalent to having forcibly restarted the
+    VM at the moment of the snapshot.
+    """
+
+    retcode, retmsg = pvc.lib.storage.ceph_snapshot_rollback(
+        CLI_CONFIG, pool, volume, name
+    )
+    finish(retcode, retmsg)
+
+
 ###############################################################################
 # > pvc storage volume snapshot list
 ###############################################################################
@@ -6349,6 +6383,7 @@ cli_storage_volume.add_command(cli_storage_volume_list)
 cli_storage_volume_snapshot.add_command(cli_storage_volume_snapshot_add)
 cli_storage_volume_snapshot.add_command(cli_storage_volume_snapshot_rename)
 cli_storage_volume_snapshot.add_command(cli_storage_volume_snapshot_remove)
+cli_storage_volume_snapshot.add_command(cli_storage_volume_snapshot_rollback)
 cli_storage_volume_snapshot.add_command(cli_storage_volume_snapshot_list)
 cli_storage_volume.add_command(cli_storage_volume_snapshot)
 cli_storage.add_command(cli_storage_volume)

client-cli/pvc/lib/storage.py

@@ -1544,6 +1544,30 @@ def ceph_snapshot_add(config, pool, volume, snapshot):
     return retstatus, response.json().get("message", "")
 
 
+def ceph_snapshot_rollback(config, pool, volume, snapshot):
+    """
+    Roll back Ceph volume to snapshot
+
+    API endpoint: POST /api/v1/storage/ceph/snapshot/{pool}/{volume}/{snapshot}/rollback
+    API arguments:
+    API schema: {"message":"{data}"}
+    """
+    response = call_api(
+        config,
+        "post",
+        "/storage/ceph/snapshot/{pool}/{volume}/{snapshot}/rollback".format(
+            snapshot=snapshot, volume=volume, pool=pool
+        ),
+    )
+
+    if response.status_code == 200:
+        retstatus = True
+    else:
+        retstatus = False
+
+    return retstatus, response.json().get("message", "")
+
+
 def ceph_snapshot_remove(config, pool, volume, snapshot):
     """
     Remove Ceph snapshot

daemon-common/ceph.py

@@ -1082,6 +1082,36 @@ def rename_snapshot(zkhandler, pool, volume, name, new_name):
     )
 
 
+def rollback_snapshot(zkhandler, pool, volume, name):
+    if not verifyVolume(zkhandler, pool, volume):
+        return False, 'ERROR: No volume with name "{}" is present in pool "{}".'.format(
+            volume, pool
+        )
+    if not verifySnapshot(zkhandler, pool, volume, name):
+        return (
+            False,
+            'ERROR: No snapshot with name "{}" is present for volume "{}" in pool "{}".'.format(
+                name, volume, pool
+            ),
+        )
+
+        # 1. Roll back the snapshot
+        retcode, stdout, stderr = common.run_os_command(
+            "rbd snap rollback {}/{}@{}".format(pool, volume, name)
+        )
+        if retcode:
+            return (
+                False,
+                'ERROR: Failed to roll back RBD volume "{}" in pool "{}" to snapshot "{}": {}'.format(
+                    volume, pool, name, stderr
+                ),
+            )
+
+    return True, 'Rolled back RBD volume "{}" in pool "{}" to snapshot "{}".'.format(
+        volume, pool, name
+    )
+
+
 def remove_snapshot(zkhandler, pool, volume, name):
     if not verifyVolume(zkhandler, pool, volume):
         return False, 'ERROR: No volume with name "{}" is present in pool "{}".'.format(