Creating snapshots and rolling back

Though backups are the most reliable and durable way to preserve Docker images and configurations, creating a backup of an entire application is not always practical. However, you need to safeguard against potential risk when changing the system. In these cases, you can create a snapshot of the system.

Snapshot functionality provides a time-efficient and space-efficient method of copying data. Create a snapshot whenever you need a save point for Docker images, such as before committing container changes.

With both snapshot and backup, Control Center

Creates a tag for the Docker image of each service with metadata about the application data.
Creates a separate snapshot of the LVM thin pool, which stores both application data and snapshots of the application data.

Snapshots are intended to serve as short-term save points only, and therefore have a default time-to-live (TTL) value of 12 hours. If you need to keep a snapshot beyond the TTL, tag the snapshot to prevent it from being deleted after the TTL expires. For historical backups of data that you need to save long-term, create full backups instead of snapshots.

You can use the rollback functionality to go back to a snapshot image. For example, roll back if changes to an application cause a failure or other degradation. Rolling back returns the application and distributed file system to the state that existed at the time of the snapshot.

Note: Rolling back from a snapshot does not remove services that you added after creating the snapshot. That is, if you create a snapshot, add a service, and then roll back, the service remains on the system; it is not deleted as part of the roll back.

Control Center uses thin provisioning, which enables it to create snapshots of the application data volume. Thin provisioning is a virtualization method that allocates data blocks only when data is written (copy-on-write).

Because snapshots track changes to the file system over time, their space requirements expand incrementally as application data changes. Application data and snapshots share the same base device; therefore, ensure that snapshots do not fill up the base device storage. For information about extending storage, see Control Center application data storage requirements.

Creating a snapshot

Log in to the Control Center host as a user with serviced CLI privileges.
Find the identifier of the service; for example, Zenoss.resmgr.
```
serviced service list
```
Create the snapshot.

Replace SERVICEID with the identifier of the service.
```
serviced snapshot add SERVICEID
```
Verify the existence of the snapshot.
```
serviced snapshot list
```
To keep the snapshot for longer than the default 12-hour TTL, tag it.

Replace SNAPSHOTID with the identifier of your snapshot and TAG-NAME with your text.
```
serviced snapshot tag SNAPSHOTID TAG-NAME
```
To make a snapshot subject to the TTL value, untag it.

Replace SNAPSHOTID with the identifier of your snapshot and TAG-NAME with your text.
```
serviced snapshot untag SNAPSHOTID TAG-NAME
```

Rolling back to a snapshot

Before rolling back, you must stop services that are used in the snapshot image. The following procedure includes this step.

Log in to the Control Center host as a user with serviced CLI privileges.
To roll back to a snapshot, you must find the identifier of the snapshot.
```
serviced snapshot list
```
Roll back to the snapshot.

Replace SNAPSHOTID with the identifier of your snapshot. The --force-restart flag automatically stops the affected services before rollback and starts them after completion.
```
serviced snapshot rollback SNAPSHOTID --force-restart
```