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Docker container linking for registry

Docker container linking allows multiple Docker containers to communicate with each other directly. In the context of a Docker [[registry|Docker Registry]], this feature is commonly used to connect a web-based user interface (UI) to the registry service, enabling visual management of container images.

Configuration

To set up a linked registry environment, two containers are typically required: the registry service itself and a web frontend container^[600-developer__docker__Dockerfile__Dockerfile-01.md].

Registry Service

First, the registry service container is started. The following command runs the registry:2 image, maps port 5000, and names the container registry-srv^[600-developer__docker__Dockerfile__Dockerfile-01.md]:

docker run -d -p 5000:5000 --name registry-srv registry:2

Linked Web UI

Next, the web UI container is launched with the --link flag. This flag connects the web container to the registry-srv container^[600-developer__docker__Dockerfile__Dockerfile__Dockerfile-01.md].

  • Container Linking: The --link registry-srv argument enables the web container to discover and connect to the registry service.
  • Environment Variables: Environment variables are passed to the web container to configure the connection details, specifically pointing to the internal registry URL^[600-developer__docker__Dockerfile__Dockerfile-01.md].

Example command: 

docker run -it -p 8080:8080 --name registry-web --link registry-srv -e REGISTRY_URL=http://registry-srv:5000/v2 -e REGISTRY_NAME=localhost:5000 hyper/docker-registry-web

In this configuration, the registry URL (http://registry-srv:5000/v2) uses the alias registry-srv, which resolves to the linked container's internal IP address^[600-developer__docker__Dockerfile__Dockerfile-01.md].

Sources