Manage relations for a 12-factor app charm

A charm integration can be added to your charmed 12-factor app by providing the integration and endpoint definition in your project file:

charmcraft.yaml
requires:
  <endpoint name>:
    interface: <endpoint interface name>
    optional: false

Here, <endpoint name> corresponds to the endpoint of the application with which you want the integration, and <endpoint interface name> is the endpoint schema to which this relation conforms. Both the <endpoint name> and <endpoint interface name> must coincide with the structs defined in the pfoject file of that particular application’s charm. The key optional with value False means that the charm will get blocked and stop the services if the integration is not provided.

You can provide the integration to your deployed 12-factor app using:

juju integrate <app charm> <endoint name>

After the integration has been established, the connection string and other configuration options will be available as environment variables that you may use to configure your 12-factor application.

For example, if you wish to integrate your 12-factor application with PostgreSQL (machine or k8s charm), add the following endpoint definition to your project file:

requires:
  postgresql:
    interface: postgresql_client
    optional: True

Provide the integration to your deployed 12-factor app with:

juju integrate <app charm> postgresql

This integration creates the following environment variables you may use to configure your 12-factor application.

  • POSTGRESQL_DB_CONNECT_STRING

  • POSTGRESQL_DB_SCHEME

  • POSTGRESQL_DB_NETLOC

  • POSTGRESQL_DB_PATH

  • POSTGRESQL_DB_PARAMS

  • POSTGRESQL_DB_QUERY

  • POSTGRESQL_DB_FRAGMENT

  • POSTGRESQL_DB_USERNAME

  • POSTGRESQL_DB_PASSWORD

  • POSTGRESQL_DB_HOSTNAME

  • POSTGRESQL_DB_PORT