Links

Links are how Docker containers talk to each other through TCP/IP ports. Atlassian show worked examples. You can also resolve links by hostname.

This has been deprecated to some extent by user-defined networks.

NOTE: If you want containers to ONLY communicate with each other through links, start the docker daemon with -icc=false to disable inter process communication.

If you have a container with the name CONTAINER (specified by docker run --name CONTAINER) and in the Dockerfile, it has an exposed port:

EXPOSE 1337

Then if we create another container called LINKED like so:

docker run -d --link CONTAINER:ALIAS --name LINKED user/wordpress

Then the exposed ports and aliases of CONTAINER will show up in LINKED with the following environment variables:

$ALIAS_PORT_1337_TCP_PORT
$ALIAS_PORT_1337_TCP_ADDR

And you can connect to it that way.

To delete links, use docker rm --link.

Generally, linking between docker services is a subset of “service discovery”, a big problem if you’re planning to use Docker at scale in production. Please read The Docker Ecosystem: Service Discovery and Distributed Configuration Stores for more info.