How to manage a controller

See also: Controller

This document demonstrates various ways in which you can interact with a controller.


Create a controller

See also: juju bootstrap

To create a juju controller in a cloud, use the bootstrap command:

juju bootstrap 

This will start an interactive session where you will be asked for the name of the cloud and the name you want to give the controller.

Alternatively, you can specify these things directly by adding the name of the cloud and of the controller right after the bootstrap command. For example, below we bootstrap a controller with the name aws-controller into our aws cloud:

juju bootstrap aws aws-controller

When you use the bootstrap command in this way (non-interactively), you can also add many different options, to specify the cloud credentials to be used, to select a specific cloud region, to specify a storage pool, to constrain the controller or workload machines, to configure the deployment in various ways, to pass a cloud-specific setting, to choose a specific juju agent version, etc.

List all controllers

See also: juju controllers

To see a list of all the controllers known to the juju client, run the controllers command:

juju controllers

Sample output for a case where there is just a single controller boostrapped into the localhost cloud:

Use --refresh option with this command to see the latest information.

Controller             Model       User   Access     Cloud/Region         Models  Nodes    HA  Version
localhost-controller*  controller  admin  superuser  localhost/localhost       1      1  none  3.0.0  

By specifying various options you can also choose a specific output format, an output file, etc.

Show details about a controller

See also: juju show-controller

To view detailed information about a controller, use the show-controller command, optionally followed by one or more controller names. For example, below we examine a controller called localhost-controller:

juju show-controller localhost-controller

By specifying various options you can also choose an output format, an output file, or get an output that includes the password for the logged in user.

Switch to a different controller

See also: juju switch

To switch from one controller to another, use the switch command followed by the name of the controller. For example, below we switch to a controller called localhost-controller-prod:

juju switch localhost-controller-prod

The switch command can also be used to switch to a different model. To remove any ambiguity, in some cases it may be safer to specify the model name explicitly on the template <controller-name>:<model-name>

Configure a controller

See also: Configuration

Set values

See also: List of controller configuration keys

A controller configuration key can be assigned a value during controller-creation time or post-creation time. The vast majority of keys are set in the former way.

Set values during controller creation

See also: juju bootstrap --config

To set a controller’s configuration at controller-creation time, use the bootstrap command with the --config followed by the relevant <key>=<value> pair(s). For example, the code below creates a controller localhost on a cloud lxd and at the same time configures the controller such that the bootstrap-timeout key is 700 seconds:

juju bootstrap --config bootstrap-timeout=700 localhost lxd

Set values after controller creation

See also: juju controller-config

To set a controller’s configuration once it’s already been created, use the controller-config command followed by the relevant <key>=<value> pair(s). For example, the code below configures an existing controller named aws so as to record auditing information, with the number of old audit log files to keep being set at 5.

juju controller-config -c aws auditing-enabled=true audit-log-max-backups=5

Get values

See also: juju controller-config

To get a controller’s current configuration, run:

juju controller-config

This will output a list of configuration keys and their values. This will include those that were set during controller creation, inherited as a default value, or dynamically set by Juju.

Register and unregister a controller

Register a controller

See also: juju register

To make a controller known to the juju client, use the register command followed by the registration key provided to you by the controller admin user or, in the case of a public controller, the DNS host name of the public controller, as shown below:

# Use a registration key:
`juju register MFATA3JvZDAnExMxMDQuMTU0LjQyLjQ0OjE3MDcwExAxMC4xMjguMC4yOjE3MDcwBCBEFCaXerhNImkKKabuX5ULWf2Bp4AzPNJEbXVWgraLrAA=`

# Use a DNS host name:
juju register

This will start an interactive session prompting you to supply a local name for the controller as well as a username and a password for you as a new juju user on the controller.

Unregister a controller

See also: juju unregister

To remove knowledge of the controller from the juju client, run the unregister command followed by the name of the controller. For example, below we unregister the controller named localhost-controller-prod:

juju unregister localhost-controller-prod

Note that this does not destroy the controller (though, to regain access to it, you will have to re-register it).

Make a controller highly available

See also: juju enable-ha, Controller high availability

To make a controller highly available, use the enable-ha command:

juju enable-ha

This will make sure that the number of controllers increases to the default minimum of 3. Sample output:

maintaining machines: 0
adding machines: 1, 2

Expand to see other ways of checking this

We can also query for machines in the ‘controller’ model:

juju machines -m controller

The output should show two new machines being provisioned:

Machine  State    DNS            Inst id              Series  AZ          Message
0        started   i-04790c2414e4c8e80  xenial  us-east-1a  running
1        pending  i-071660e9ce3c3cee5  xenial  us-east-1c  running
2        pending   i-0b36284d1ebb816cf  xenial  us-east-1a  running

Invoking juju enable-ha again would have no effect since 3 controllers are already present.

Refreshing the list of controllers with juju controllers --refresh displays an HA level of 3:

Controller  Model    User   Access     Cloud/Region         Models  Machines    HA  Version
aws-ha*     default  admin  superuser  aws/us-east-1             2         3     3  2.4-beta2

Optionally, you can also mention a specific controller and also the number of controller machines you want to use for HA, among other things (e.g., constraints).

The number of controllers must be an odd number in order for a master to be “voted in” amongst its peers. A cluster with an even number of members will cause a random member to become inactive. This latter system will become a “hot standby” and automatically become active should some other member fail. Furthermore, due to limitations of the underlying database in an HA context, that number cannot exceed seven. All this means that a cluster can only have three, five, or seven active members.

If a controller is misbehaving, or if you’ve decided that you don’t need as many controllers for HA after all, you can remove them. To remove a controller, remove its machine from the controller model via the remove-machine command.

The enable-ha command cannot be used to remove machines from the cluster.

For example, below we remove controller 1 by removing machine 1 from the controller model:

juju remove-machine -m controller 1

If the removal of a controller will result in an even number of systems then one will act as a “hot standby”.
If the removal of a controller will result in an odd number of systems then each one will actively participate in the cluster.

The output to juju controllers --refresh now becomes as below, where the HA column says 1/2 – that is, there is now a single active controller, with the remaining controller on standby.

Controller  Model    User   Access     Cloud/Region         Models  Machines    HA  Version
aws-ha*     default  admin  superuser  aws/us-east-1             2         2   1/2  2.4-beta2

Back up a controller

This section demonstrates the various steps involved in backing up a controller.

The procedure documented below is currently supported only for machine (non-Kubernetes) controllers.

Create a controller backup

See also: juju create-backup

To create a backup of a controller configuration / metadata, use the create-backup followed by the -m flag and the name of the target controller model. For example, assuming a controller called localhost-controller, and the standard controller model name (controller), we will do:

juju create-backup -m localhost-controller:controller

Alternatively, you can switch to the controller model and use this command without any arguments or use the -m flag followed by just controller. However, due to the delicate nature of data backups, the verbose but explicit method demonstrated above is highly recommended.

Sample output:

backup format version: 1 
juju version:          3.0.0 
base:                  ubuntu@22.04 

controller UUID:       ca60f7e9-647b-4460-8232-fe75749e17c7
model UUID:            a04d7604-3073-45b7-871f-030ac0360fb4 
machine ID:            0 
created on host:       juju-360fb4-0 

checksum:              BrOGsXIK375529xlXJHX7m23Amk= 
checksum format:       SHA-1, base64 encoded 
size (B):              114919198 
stored:                0001-01-01 00:00:00 +0000 UTC 
started:               2022-11-09 09:06:46.800165238 +0000 UTC 
finished:              2022-11-09 09:07:05.133077079 +0000 UTC 


Downloaded to juju-backup-20221109-090646.tar.gz

The backup is downloaded to a default location on your computer (e.g., /home/user). A backup of a fresh (empty) environment, regardless of cloud type, is approximately 75 MiB in size.

The create-backup command also allows you to specify a custom filename for the backup file (--filename <custom-filename>). Note: You can technically also choose to save the backup on the controller (--no-download), but starting with juju v.3.0 this flag is deprecated.

Download a controller backup

See also: juju download-backup

Suppose you’ve created a backup with the --no-download option, as shown below (where controller is the name of the controller model).

Starting with juju v.3.0, this flag is deprecated.

$ juju create-backup -m controller --no-download
WARNING --no-download flag is DEPRECATED.

backup format version: 1 
juju version:          3.0.0 
base:                  ubuntu@22.04 

controller UUID:       ca60f7e9-647b-4460-8232-fe75749e17c7
model UUID:            a04d7604-3073-45b7-871f-030ac0360fb4 
machine ID:            0 
created on host:       juju-360fb4-0 

checksum:              tjqEvlspc88mYQmjV9u/m4i+prg= 
checksum format:       SHA-1, base64 encoded 
size (B):              114919131 
stored:                0001-01-01 00:00:00 +0000 UTC 
started:               2022-11-09 09:08:51.314128218 +0000 UTC 
finished:              2022-11-09 09:09:10.296320799 +0000 UTC 


Remote backup stored on the controller as /tmp/juju-backup-20221109-090851.tar.gz

As you can see from the output, this has resulted in the backup being saved remotely on the controller as /tmp/juju-backup-20221109-090851.tar.gz.

To download the backup, use the download-backup command followed by the remote location of the backup. In our case:

juju download-backup /tmp/juju-backup-20221109-090851.tar.gz

This will output the name of the downloaded backup file. In our case:


This file will have been downloaded to a temporary location (in our case, /home/user).

Restore a controller from a backup

See also: juju-restore

To restore a controller from a backup, you can use the stand-alone juju-restore tool.

First, download the juju-restore tool and copy it to the primary controller machine in the MongoDB replica set (typically, machine 0). To identify the primary controller machine, you can use the juju show-controller – its output will list all the machines and the primary will contain ha-primary: true:

juju show-controller
      instance-id: i-073443a840f1a3626
      ha-status: ha-enabled
      ha-primary: true
      instance-id: i-0be2c1b818e54a2ba
      ha-status: ha-enabled
      instance-id: i-0b4705ede7d3c0faa
      ha-status: ha-enabled

Then you can copy the restore tool:

# Download the latest release binary (Linux, AMD64):
chmod +x juju-restore

# Switch to the controller model:
juju switch controller

# Copy juju-restore to the primary controller machine:  
juju scp juju-restore 0:

Second, assuming that during the create-backup step you chose to save a local copy (the default option), use scp to copy the file to the same controller machine, as shown below.

juju scp <path-to-backup> 0:

If you’ve used create-download with the --no-download option, you can skip this step – the backup is already on the primary controller machine.

Now, SSH into this machine and run ./juju-restore followed by the path to the backup file, as shown below. All replica set nodes need to be healthy and in PRIMARY or SECONDARY state.

# SSH into the controller machine
juju ssh 0

# Start the restore! (it will ask for confirmation)
./juju-restore <path-to-backup>

The juju-restore tool also provides several options, among which:

  • --yes: answer “yes” to confirmation prompts (for non-interactive mode)
  • --include-status-history: restore the status history collection for machines and units (which can be large, and usually isn’t needed)
  • --username, --password, and related options: override the defaults for connecting to MongoDB
  • --allow-downgrade: restore from a backup created with an earlier juju version
  • --manual-agent-control: (in the case of restoring backups to high availability controllers) stop and restart juju agents and Mongo daemons on the secondary controller machines manually
  • --copy-controller: clone the configuration of an old controller into a new controller (download the latest juju-restore to see this option).
    Note: This feature is useful in upgrading to 3.0. See How to upgrade your deployment from 2.9 to 3.0.

For the full list of options, type: ./juju-restore --help

Upgrade a controller

The procedure for upgrading a controller depends on whether you’re upgrading it across patch versions or rather minor or major versions.

Upgrade a controller across patch versions

See also: upgrade-controller, juju upgrade-model -m controller

To upgrade a controller across patch versions (e.g., v.2.9.25 -> v.2.9.26 ), use the upgrade-controller command (or, equivalently, upgrade-model -m controller):

juju upgrade-controller

By using various options you can make this into just a simulation of an upgrade, or choose a specific agent version to upgrade to, or choose a timeout, etc.

When you want to upgrade the controller but the controller is without internet access, you can copy agent binaries from the official agent store into the controller via an internet-connected client by using the juju sync-agent-binary command: juju sync-agent-binary. By passing various options you can also specify a local destination directory, a version, etc.

Upgrade a controller across minor or major versions

See also: Create a controller

If you want to upgrade a controller across minor (e.g., v.2.7 -> v.2.8 ) or major versions (v.2 -> v.3 ), you cannot do this in place via the upgrade-controller command. Instead, you must bootstrap a new controller.

Remove a controller

See also: Removing things

There are two ways to remove a controller. Below we demonstrate each, in order of severity.

For how to remove knowledge about a controller from a juju client, see Unregister a controller.

Destroy a controller

See also: juju destroy-controller

A controller can be destroyed with:

juju destroy-controller <controller-name>

You will always be prompted to confirm this action. Use the -y option to override this.

As a safety measure, if there are any models (besides the ‘controller’ model) associated with the controller you will need to pass the --destroy-all-models option.

Additionally, if there is persistent storage in any of the controller’s models you will be prompted to either destroy or release the storage, using the --destroy-storage or --release-storage options respectively.

For example:

juju destroy-controller -y --destroy-all-models --destroy-storage aws

Any model in the controller that has disabled commands will block a controller from being destroyed. A controller administrator is able to enable all the commands across all the models in a Juju controller so that the controller can be destroyed if desired. This can be done via the enable-destroy-controller command: juju enable-destroy-controller.

Use the kill-controller command as a last resort if the controller is not accessible for some reason.

Kill a controller

See also: juju kill-controller

The kill-controller command deserves some attention as it is very destructive and also has exceptional behaviour modes. This command will first attempt to remove a controller and its models in an orderly fashion. That is, it will behave like destroy-controller. If this fails, usually due the controller itself being unreachable, then the controller machine and the workload machines will be destroyed by having the client contact the backing cloud’s API directly.

Last updated a month ago.