Understanding Dockerfile CMD: Default Runtime Commands and How to Override Them

The Dockerfile CMD instruction defines the default command that runs when a container starts, distinguishing it from RUN, which executes only during the image build process. Without a CMD instruction, a Docker container starts and immediately exits because it has no primary process to keep it alive. For example, a Go server image built without CMD requires manual execution of 'go run server.go' inside the container each time it starts. Adding CMD ["go", "run", "server.go"] to the Dockerfile automates this, launching the server as soon as the container runs. CMD can also be overridden at runtime by passing a different command to 'docker run', giving developers flexible control over container behavior.