Creating server backups is an important step in production deployments. Backups
provide a mechanism for the server to recover from an outage (network loss,
operator error, or a corrupted data directory). All servers write to the
-data-dir before commit on write requests. The same directory is used on
client agents to persist local state too, but this is not critical and can be
rebuilt when recreating an agent. Local client state is not backed up in this
tutorial, and doesn't need to be in general, only the server's Raft store state.
Consul provides the snapshot
command which can be run using the CLI or the API. The
snapshot command saves
a point-in-time snapshot of the state of the Consul servers which includes, but
is not limited to:
- Key-Value entries
- the service catalog
- prepared queries
With Consul Enterprise,
snapshot agent command runs periodically and writes to local or remote
storage (such as Amazon S3).
By default, all snapshots are taken using
consistent mode where requests are
forwarded to the leader which verifies that it is still in power before taking
the snapshot. Snapshots will not be saved if the Consul datacenter is degraded
or if no leader is available. To reduce the burden on the leader, it is possible
to run the snapshot on
any non-leader server using
stale consistency mode.
This spreads the load across nodes at the possible expense of losing full
consistency guarantees. Typically this means that a very small number of recent
writes may not be included. The omitted writes are typically limited to data
written in the last
100ms or less from the recovery point. This is usually
suitable for disaster recovery. However, the system can't guarantee how stale
this may be if executed against a partitioned server.
snapshot save command for backing up the Consul cluster state has many
configuration options. In a production environment, you will want to configure
ACL tokens and client certificates for security. The configuration options also
allow you to specify the Consul cluster and server to collect the backup data
from. Below are several examples.
First, you will run the basic snapshot command on one of the servers using the
default configuration, including
$ consul snapshot save backup.snap Saved and verified snapshot to index 1176
The backup will be saved locally in the directory where you ran the command.
You can view metadata about the backup with the
$ consul snapshot inspect backup.snap ID 2-1182-1542056499724 Size 4115 Index 1182 Term 2 Version 1
To understand each field review the inspect
Version field does not correspond to the version of the data.
Rather it is the snapshot format version.
Next, you will collect the Consul cluster data from a non-leader by specifying stale mode.
$ consul snapshot save -stale backup.snap Saved and verified snapshot to index 2276
Once ACLs and agent certificates are configured, they can be passed in as environment variables or flags.
$ export CONSUL_HTTP_TOKEN=<your ACL token>
$ consul snapshot save -stale -ca-file=</path/to/file> backup.snap Saved and verified snapshot to index 2287
In the above example, you set the token as an ENV and the ca-file with a command line flag.
For production use, the
snapshot save command or
API should be scripted and run
frequently. In addition to frequently backing up the Consul cluster state, there
are several use cases when you would also want to manually execute
First, you should always backup the Consul cluster before upgrading. If the
upgrade does not go according to plan it is often not possible to downgrade due
to changes in the state store format. Restoring from a backup is the only option
so taking one before the upgrade will ensure you have the latest data. Second,
if the Consul cluster loses quorum it may be beneficial to save the state before
the servers become divergent. Finally, you can manually snapshot a Consul
datacenter and use that to bootstrap a new Consul datacenter with the same state.
Operationally, the backup process does not need to be executed on every server.
Additionally, you can use the configuration options to save the backups to a
mounted filesystem. The mounted filesystem can even be cloud storage, such as
Amazon S3. The enterprise command
snapshot agent automates this process.
restore process should be straightforward. However, there are a
couple of actions you can take to ensure the process goes smoothly. First, make
sure the Consul datacenter you are restoring is stable and has a leader. You can
verify this using
consul operator raft list-peers and checking server logs and
telemetry for signs of leader elections or network issues.
You will only need to run the process once, on the leader. The Raft consensus protocol ensures that all servers restore the same state.
$ consul snapshot restore backup.snap Restored snapshot
save subcommand, restore has many configuration options. In
production, you would again want to use ACLs and certificates for security.
In this tutorial, you learned about the
snapshot save and
commands. If you are testing the backup and restore process, you can add an
extra dummy value to Consul KV. Another indicator that the backup was saved
correctly is the size of the backup artifact.