ENTRYPOINT Vs CMD in Docker
CMD Vs Entrypoint is a bit confusing at the beginning. When should you use CMD and when should you use ENTRYPOINT while building your docker images?
CMD
This is the command that runs when you start a container.
Eg:
cmd-docker
FROM ubuntu
CMD [ "echo" , "this is running from CMD which runs when the container starts" ]
Building an image:
docker build -t cmd-docker -f cmdvsentrypoint.yaml .
Default docker run:
docker run cmd-docker
this is running from CMD which runs when the container starts
Docker run with external command as input
docker run cmd-docker echo this is passed as startup argument
this is passed as startup argument
ENTRYPOINT
This is just the starting program without the options/arguments.
Sample:
FROM ubuntu
ENTRYPOINT [ "echo" ]
docker build: docker build -t entrypoint -f entrypoint.yaml .
default run:
docker run entrypoint
(there is no output since we just have echo and didn’t pass an argument)
docker run with argument:
docker run entrypoint hello
hello
docker run entrypoint echo hello
echo hello
(This is equivalent to echo echo hello world)