Linking Acorn Apps
Acorn apps can link to containers from other Acorn apps at runtime to provide supporting services. For instance, if you have an Acorn running PostgreSQL, it can be used to provide the db service to another app.
If you have an Acorn that defines a web container and a redis container, you can consume a separate Acorn to provide the redis service from an already running Acorn.
acorn run --link my-other-redis-acorn:redis [IMAGE]
In the above example, the container service from the running Acorn will be available within the new Acorn as redis. Your new instance will be able to resolve the redis name and it will connect to the remote service defined by the link.
The port from the container being linked to must be explicitly exposed in the Acornfile i.e. ports: expose: "5432/tcp".
The more general linking syntax is as follows:
acorn run --link <source>:<alias> [IMAGE]
<alias> is the name that the new Acorn app can use to resolve the linked service.
<source> is one of the following:
- The name of another Acorn in the same project, if that Acorn only has one container
- A reference to a particular container in a different Acorn in the same project, in the format
<acorn>.<container>
For example, if I have an Acorn called my-app with two containers nginx and db, I can link the db container to another Acorn in the same project:
acorn run --link my-app.db:db [IMAGE]
If you set the <alias> to a name identical to the name of one of the containers in the new app, then that container in the new app will not be created, since the linked container takes its place.