What is the difference between CMD and ENTRYPOINT in a Dockerfile?

The distinction between CMD and ENTRYPOINT in a Dockerfile is essential for understanding how containers are run. When you designate a command in a Dockerfile, you often need to understand how CMD and ENTRYPOINT work together.

The appropriate answer highlights that CMD can indeed provide default arguments to ENTRYPOINT, which is the main command that gets executed when a container starts. This means that if you set up ENTRYPOINT as the primary executable, CMD could supply additional command-line arguments to that executable. For example, if you specify ENTRYPOINT as an application (like a shell or a specific program), CMD can provide the parameters that you want that application to run with by default.

In scenarios where only CMD is defined, Docker will consider it as the command to run when the container starts. However, if both CMD and ENTRYPOINT are specified, CMD values will be used as arguments to the ENTRYPOINT. This allows for more versatility and configurability in running containers, making it easier to override CMD arguments at runtime without changing the ENTRYPOINT.

Understanding this relationship helps in creating more efficient and adaptable Docker images tailored to specific needs or different environments, while also allowing users to modify the parameters without changing the main executable logic defined in ENTRYPOINT.