Removing applications, units, and machines

Juju can sanely and efficiently remove something when you no longer need it. This section looks at how to remove applications, units, and machines. To remove a model see the models documentation. To remove a controller, see the controllers documentation.

Removing an application

Once an application is no longer required it can be removed with:

juju remove-application <application-name>

Note: Removing an application which has active relations with another running application will terminate that relation. Charms are written to handle this, but be aware that the other application may no longer work as expected. To remove relations between deployed applications, see Charm relations.

This is the order of events for removing an application:

  1. The Juju client tells the state server that every unit (in this application) is to be destroyed.
  2. The state server signals to the application (charm) that it is going to be destroyed.
  3. The charm breaks any relations to its application by calling relationship-broken and relationship-departed.
  4. The charm calls its 'stop hook' which should:
    • Stop the application
    • Remove any files/configuration created during the application lifecycle
    • Prepare any backup(s) of the application that are required for restore purposes.
  5. The application and all its units are then removed.

An application can take a while to "die", but if juju status reveals that the application is listed as dying, but also reports an error state, then the removed application will not go away. See the 'Caveats' section below for how to manage applications stuck in a dying state.

If dynamic storage is in use, the storage will, by default, be detached and left alive in the model. However, the --destroy-storage option can be used to instruct Juju to destroy the storage once detached. See Using Juju Storage for details on dynamic storage.

Removing units

It is possible to remove individual units instead of the entire application:

juju remove-unit mediawiki/1

To remove multiple units:

juju remove-unit mediawiki/1 mediawiki/2 mediawiki/3 mysql/2

In the case that these are the only units running on a machine, unless that machine was created manually with juju add machine, the machine will also be removed.

See section 'Caveats' below for how to manage units in a dying state.

The --destroy-storage option is available for this command as it is for the remove-application command above.

Removing machines

Juju machines can be removed like this:

juju remove-machine <number>

However, it is not possible to remove a machine which is currently allocated to a unit. If attempted, this message will be emitted:

error: no machines were destroyed: machine 3 has unit "mysql/0" assigned

By default, when a Juju machine is removed, the backing system, typically a cloud instance, is also destroyed. The --keep-instance option overrides this; it allows the instance to be left running.

Caveats

These are caveats which you may encounter while removing items.

state of life: dying

If you have a unit or application that persists in a dying state check to see if that unit, or any units within the associated application, are in an error state. A "removal" is an event within the queue of a unit's lifecycle so when a unit enters an error state all events within the queue are blocked. To unblock the unit's error you need to resolve it. Do so like this:

juju resolved <unit>

The above command may need to be repeated to resolve other errors on the unit.

There may be errors on other units caused by the breaking of relations that occur when removing a unit or application. Therefore also verify that the associated units are not in an error state and apply the above command to them if they are.