Controller backups

A backup of a controller enables one to re-establish the configuration and state of a controller. It does not influence workload instances on the backing cloud. That is, if such an instance is terminated directly in the cloud then a controller restore cannot re-create it.

This page will cover the following topics:

  • Creating a backup
  • Managing backups
  • Restoring from a backup
  • High availability considerations

Note: Data backups can also be made of the Juju client. See the Juju client page for guidance.

The Juju controller

Juju provides commands for recovering a controller in case of breakage or in the case where the controller no longer exists.

The current state is held within the 'controller' model. Therefore, all backup commands need to operate within that model explicitly or by ensuring the current model is the 'controller' model. In the examples provided below, both the controller name and the model name are expressed explicitly (e.g. -m aws:controller). Due to the delicate nature of data backups, this method is highly recommended.

Creating a backup

The create-backup command is used to create a backup. It does so by generating an archive, storing it on the controller (a remote backup), and downloading it to the Juju client system as a 'tar.gz' file (a local backup). With the aid of the --no-download option a local backup can be prevented.

The name of the backup is composed of the creation time (in UTC) and a unique identifier.

The below examples assume the existence of the following controllers (output to juju controllers):

Controller  Model    User   Access     Cloud/Region         Models  Machines    HA  Version
aws         default  admin  superuser  aws/us-east-1             2         1  none  2.3.7  
lxd*        default  admin  superuser  localhost/localhost       2         1  none  2.3.7

To create a backup of the 'aws' controller:

juju create-backup -m aws:controller

Sample output:

downloading to juju-backup-20180515-191942.tar.gz

The first line shows the remote backup and the second line shows the local backup. From the name of the remote archive we see that the backup was made on May 15, 2018 at 19:19:42 UTC.

Warning: Archive filenames do not include the associated controller name. Care should therefore be taken when archiving from multiple controllers. To specify a custom name use the --filename option. This option does not affect the remote archive name.

To create a backup of the 'lxd' controller while both using a custom filename and adding an optional note:

juju create-backup -m lxd:controller --filename juju-backup-lxd-20180515-193724.tar.gz "fresh lxd controller"

The optional note is exposed via the show-backup command detailed below.

Note: A backup of a fresh (empty) environment, regardless of cloud type, is approximately 56 MiB in size.

Managing backups

The following commands are available for managing backups (apart from restoring):

  • juju backups
  • juju show-backup
  • juju download-backup
  • juju upload-backup
  • juju remove-backup

juju backups

The backups command displays the names of all remote backups for a given controller. For instance, to see all remotely stored backups for the 'lxd' controller:

juju backups -m lxd:controller

Sample output:


juju show-backup

The show-backup command provides a metadata record for a specific remote backup (identified via the backups command). For example, to query a backup stored on the 'lxd' controller:

juju show-backup -m lxd:controller 20180515-195557.9c6a3650-2957-489a-8f0c-6c3b5ce2e055

Sample output:

backup ID:       "20180515-193724.9c6a3650-2957-489a-8f0c-6c3b5ce2e055"
checksum:        "pmxx7bCwtZVV+KM48YKz5w6Boc0="
checksum format: "SHA-1, base64 encoded"
size (B):        58605244
stored:          2018-05-15 19:40:28 +0000 UTC
started:         2018-05-15 19:37:24 +0000 UTC
finished:        2018-05-15 19:37:41 +0000 UTC
notes:           "fresh lxd controller"
model ID:        "9c6a3650-2957-489a-8f0c-6c3b5ce2e055"
machine ID:      "0"
created on host: "juju-e2e055-0"
juju version:    2.3.7

The started time is the most pertinent of the various timestamps. It refers to the time the backup was created.

juju download-backup

The download-backup command downloads a specific remote backup (again, identified via the backups command). Here, we download a backup that is stored on the 'aws' controller:

juju download-backup -m aws:controller 20180515-191942.7e45250b-637a-4dc9-8389-c6aa70100cd6

juju upload-backup

The upload-backup command uploads a specific local backup to a controller. For example:

juju upload-backup -m lxd:controller juju-backup-20180515-193724.tar.gz

Note: It is not possible to upload a file that is equivalent to a backup stored remotely. The process will be cancelled and an error message will be printed.

juju remove-backup

The remove-backup command removes a specific remote backup from a controller. For instance:

juju remove-backup -m aws:controller 20180515-191942.7e45250b-637a-4dc9-8389-c6aa70100cd6

Restoring from a backup

To revert the state of an environment to a previous time the restore-backup command is used.

Warning: The restore process does not validate that a backup archive corresponds to the controller it was created from. Make sure you do not overwrite a controller with the wrong backup.

This command requires the use of the --id option when referring to a remote backup:

juju restore-backup -m lxd:controller --id 20180515-193724.9c6a3650-2957-489a-8f0c-6c3b5ce2e055

To apply a local backup the --file option must be used:

juju restore-backup -m lxd:controller --file juju-backup-lxd-20180515-193724.tar.gz

To create a new controller during a data restore the -b option is used:

juju restore-backup -b --file backup.tar.gz

Note: It is not possible to restore using a local backup that is equivalent to a remote backup. The process will be cancelled and an error message will be printed. The remote backup should just be used instead.

High availability considerations

Although Controller high availability makes for a more robust (and load balanced) Juju infrastructure, it should not replace the need for data backups. It does, however, make the prospect of restoring from backup less likely, since as long as one controller cluster member remains operational, the others can be replaced via the enable-ha command. A restore in an HA scenario therefore only becomes necessary when all controllers have failed. However, if a restore is applied to a cluster with active members all reachable controllers will naturally have their data overwritten.

Restoring to a cluster

It is not possible at this time to restore while HA is enabled.

To restore to an HA cluster one needs to first remove HA (by removing all but one of the controller machines) and then perform a restore operation. HA may then be re-enabled afterwards.

For example, consider a three-member cluster with machines '0', '1', and '2' in the 'controller' model and where a backup of the cluster was previously made (aws-ha3.tar.gz).

Here, we begin by removing machines '1' and '2' but you can remove any two:

juju remove-machine -m aws:controller 1 2

Now wait until Juju reports that it is in a non-HA state. This is indicated by the text 'none' under the 'HA' column in the output to the controllers command:

juju controllers

Sample output:

Controller  Model    User   Access     Cloud/Region   Models  Machines    HA  Version
aws*        default  admin  superuser  aws/us-east-1       3         2  none 2.4-rc1

There should now be only a single machine listed in the output to juju machines -m aws:controller.

We can now restore:

juju restore-backup -m aws:controller --file aws-ha3.tar.gz

After a while the two removed machines will reappear but in a 'down' state:

Machine  State    DNS            Inst id              Series  AZ          Message
0        started  i-0095fa21cda2b3b9c  xenial  us-east-1a  running
1        down  i-08105aeb4e04a26e2  xenial  us-east-1a  running
2        down   i-0e6417bf06d36498b  xenial  us-east-1c  running

Remove them by force:

juju remove-machine -m aws:controller 1 2 --force

You can now re-enable HA if desired:

juju enable-ha -c aws

See Controller high availability for guidance on using the enable-ha command.

Restoring due to complete cluster failure

In the advent that all controllers are unresponsive the following steps should be taken:

  1. Remove the cluster
  2. Perform a data restore and create a new controller
  3. Enable HA

To demonstrate this, consider an initial AWS-based controller named 'aws-ha3-1' with three cluster members:

juju kill-controller aws-ha3-1
juju restore-backup -b --file backup.tar.gz
juju enable-ha -n 3

Note: Section Recovering from controller failure details how to deal with a partially degraded cluster.

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