What is entrypoint and cmd in the context of Docker?

ENTRYPOINT defines the command that will be executed when the container starts. If CMD or command parameters are passed during docker run, they are added as arguments to this command.

CMD provides default arguments for ENTRYPOINT or is executed as a separate command if ENTRYPOINT is not defined. If parameters are passed during container startup, they override the CMD value.

Differences:

Feature	ENTRYPOINT	CMD
Purpose	Defines the main command to execute	Provides default arguments or command
Override	Requires docker run --entrypoint	Overridden by arguments in docker run
Usage with ENTRYPOINT	Arguments for ENTRYPOINT	Default command if ENTRYPOINT is not set

Examples:

Using ENTRYPOINT and CMD:

# Dockerfile
FROM alpine:latest
ENTRYPOINT ["echo", "Hello"]
CMD ["World!"]

Running docker run your-image-name: Executes echo Hello World! Running docker run your-image-name Universe!: Executes echo Hello Universe!

Using only CMD:

# Dockerfile
FROM alpine:latest
CMD ["echo", "Hello World!"]

Running docker run your-image-name: Executes echo Hello World! Running docker run your-image-name echo Hello Docker!: Overrides CMD, executes echo Hello Docker!

It is recommended to use ENTRYPOINT for the executable file and CMD for passing default parameters to this executable.