Docker image as Curl command

In the previous example we installed "curl" in Docker image so we could use it in the container, but we did not make any special arrangement for curl. Using that image it is equally easy to run any other Linux command available in the image. What if we would like to make executing curl the default behavior just as we had with echo?

We could include something like CMD curl in the Dockerfile, but then it would default to download the given page.

We could use CMD curl and hope to pass the URL to the docker run command, but the parameters given on the command-line will override everything we have in CMD.

However there is another tool called ENTRYPOINT. It is very similar to CMD, but in certain situations it allows the *addition* of parameters instead of the overwriting of parameters.

FROM ubuntu:20.04

RUN apt-get update
RUN apt-get install -y curl


$ docker build -t mydocker .

$ docker run --rm  mydocker
curl: try 'curl --help' or 'curl --manual' for more information

$ docker run --rm  mydocker