6.1.1.5 Creation Metadata Registration

Creation metadata registration is the step where Docker records a new container's identifying information — its ID, name, configuration, and creation timestamp — within the daemon's internal bookkeeping, making that container discoverable and manageable through subsequent commands.

What Gets Registered

At creation, Docker assigns the container a unique ID, records its configuration (the image used, environment variables, resource limits, network settings), and stores a timestamp marking exactly when this occurred.

docker create --name myapp myapp:1.0
docker inspect myapp --format '{{.Id}} {{.Created}}'

This reveals the container's full unique ID and precise creation timestamp, both established during this registration step.

Why a Container Name Must Be Unique

Because the daemon registers containers by name as well as by ID, attempting to create a second container with a name already in use by an existing container fails, since the registration step cannot record two entries under the same name.

docker create --name myapp myapp:1.0
docker create --name myapp myapp:2.0

The second command fails with a naming conflict error, since myapp is already registered as the name of an existing container.

Querying Registered Containers

Once registered, a container's metadata becomes queryable through standard commands, regardless of whether the container is actually running.

docker ps -a --filter "name=myapp"

Why Metadata Registration Matters

This registration step is what makes a created container a genuinely manageable entity within Docker's bookkeeping — without it, there would be no reliable way to reference, inspect, or control a specific container after the moment of its creation, making this an essential, if largely invisible, part of how every container comes into existence.