How to manage relations

To set up a relation between two applications on the same model, run the integrate command followed by the names of the applications. For example:

juju integrate mysql wordpress

This will satisfy WordPress’s database requirement where MySQL provides the appropriate schema and access credentials required for WordPress to run properly.

The code above however works only if there is no ambiguity in what relation the charm requires and what the related charm provides.

If the charms in question are able to establish multiple relation types, Juju may need to be supplied with more information as to how the charms should be joined. For example, if we try instead to relate the ‘mysql’ charm to the ‘mediawiki’ charm:

juju integrate mysql mediawiki 

the result is an error:

error: ambiguous relation: "mediawiki mysql" could refer to
  "mediawiki:db mysql:db"; "mediawiki:slave mysql:db"

The solution is to be explicit when referring to an endpoint, where the latter has a format of <application>:<application endpoint>. In this case, it is ‘db’ for both applications. However, it is not necessary to specify the MySQL endpoint because only the MediaWiki endpoint is ambiguous (according to the error message). Therefore, the command becomes:

juju integrate mysql mediawiki:db

See more: juju integrate

To add a same-model relation, create a resource of the juju_integration type, give it a label (below, this), and in its body add:

• a model attribute specifying the name of the model where you want to create the relation;
• two application blocks, specifying the names of the applications that you want to integrate (and, if necessary, their endpoints_;
• a lifecycle block with the replace_triggered_by argument specifying the list of application attributes (always the name, model, constraints, placement, and charm name) for which, if they are changed = destroyed and recreated, the relation must be recreated as well.

resource "juju_integration" "this" {
  model = juju_model.development.name
  via   = "10.0.0.0/24,10.0.1.0/24"

  application {
    name     = juju_application.wordpress.name
    endpoint = "db"
  }

  application {
    name     = juju_application.percona-cluster.name
    endpoint = "server"
  }

  # Add any RequiresReplace schema attributes of
  # an application in this integration to ensure
  # it is recreated if one of the applications
  # is Destroyed and Recreated by terraform. E.G.:
  lifecycle {
    replace_triggered_by = [
      juju_application.wordpress.name,
      juju_application.wordpress.model,
      juju_application.wordpress.constraints,
      juju_application.wordpress.placement,
      juju_application.wordpress.charm.name,
      juju_application.percona-cluster.name,
      juju_application.percona-cluster.model,
      juju_application.percona-cluster.constraints,
      juju_application.percona-cluster.placement,
      juju_application.percona-cluster.charm.name,
    ]
  }
}

See more: juju_integration (resource), Terraform | lifecycle > replace_triggered_by

To integrate two applications, on a connected Model, use the integrate() method.

await my_model.integrate('mysql', 'mediawiki')

# Integrate with particular endpoints
await my_model.integrate('mysql', 'mediawiki:db')

See more: integrate()

To view the current relations in the model, run juju status --relations. The example below shows a peer relation and a regular relation:

[...]
Relation provider  Requirer       Interface  Type     Message
mysql:cluster      mysql:cluster  mysql-ha   peer     
mysql:db           mediawiki:db   mysql      regular

To view just a specific relation and the applications it integrates, run juju status --relations followed by the provider and the requirer application (and endpoint). For example, based on the output above, juju status --relations mysql mediawiki would output:

[...]
Relation provider  Requirer       Interface  Type     Message  
mysql:db           mediawiki:db   mysql      regular

See more: juju status --relations

The terraform juju client does not support this. Please use the juju client.

To view the current relations in a model, directly access the Model’s relations property.

my_model.relations

See more: Model.relations (property)

To get the ID of a relation, for any unit participating in the relation, run the show-unit command – the output will also include the relation ID. For example:

$ juju show-unit synapse/0
  
...
  - relation-id: 7
    endpoint: synapse-peers
    related-endpoint: synapse-peers
   application-data:
      secret-id: secret://1234
    local-unit:
      in-scope: true

The terraform juju client does not support this. Please use the juju client.

The python-libjuju client does not support this. Please use the juju client.

Regardless of whether the relation is same-model or cross-model, to remove an relation, run the remove-relation command followed by the names of the two applications involved in the integration:

juju remove-relation <application-name> <application-name>

For example:

juju remove-relation mediawiki mysql

In cases where there is more than one relation between the two applications, specify the interface at least for one of the applications:

juju remove-relation mediawiki mysql:db

See more: juju remove-relation

To remove a relation, in your Terraform plan, remove its resource definition.

See more: juju_integration (resource)

To remove a relation, use the remove_relation() method on an Application object.

await my_app.remove_relation('mediawiki', 'mysql:db')

See more: remove_relation()