Configuring applications

When deploying an application, the charm you use will often support or even require specific configuration options to be set.

Juju provides tools to help manage these options and respond to changes over the lifetime of the application. These options apply to the entire application, as opposed to only a specific unit or relation. The configuration can be done at deployment time or post-deployment.

Discovering application configuration options

Each charm will have its own set of options and possible values. You can discover these in several ways:

  • by running the config command
  • by viewing the charm in the Charm Store
  • by examining the config.yaml file in the charm itself

Configuring an application at deployment time

Configuration values can be set at deployment time using the following methods:

  • by using a yaml-formatted file
  • by passing options/values directly on the command line
  • a combination of the above

All these methods use the --config option.

For example, upon investigation we discover that the Mediawiki charm allows us to set values for the 'name' of the wiki and the 'skin' to use. We can put these inside a configuration file.

  name: Juju Wiki
  skin: monobook

Assuming the file is called myconfig.yaml, the application can be deployed and configured in this way:

juju deploy --config myconfig.yaml mediawiki

Warning: If the configuration file cannot be read or contains syntax errors or invalid options, an error message will be printed to this effect. However, the application will still be deployed .

To pass the options directly:

juju deploy --config name='Juju Wiki' --config skin='monobook'

A combination can also be used. If a duplication arises, the last-mentioned value gets used. For instance, below, the wiki will be assigned the name of 'Juju Wiki':

juju deploy --config name='Juju Wookie' --config myconfig.yaml

Configuring an application post deployment

It is possible to set or change the configuration of an application which is already deployed.

Before you set any of these options, you may want to check what current options are already set. For example:

juju config mediawiki

Should return something like this:

application: mediawiki
charm: mediawiki
    description: Admin users to create, user:pass
    is_default: true
    type: string
    value: ""
    description: turn on debugging features of mediawiki
    is_default: true
    type: boolean
    value: false
    description: URL to fetch logo from
    is_default: true
    type: string
    value: ""
    description: The name, or Title of the Wiki
    is_default: true
    type: string
    value: Please set name of wiki
    description: The server url to set "$wgServer". Useful for reverse proxies
    is_default: true
    type: string
    value: ""
    description: skin for the Wiki
    is_default: true
    type: string
    value: vector
    description: If we should put '/mediawiki' suffix on the url
    is_default: true
    type: boolean
    value: true

You can set the options in a very similar way. Simply add space-separated key=value pairs as arguments:

juju config mediawiki skin=monoblock name='Juju Wiki'

It is also possible to set options from a YAML file:

juju config mediawiki --file path/to/myconfig.yaml

Setting an option back to its default value is achieved with the --reset option. Here, the argument is a comma-separated list of the option names in question:

juju config mediawiki --reset admins,name