Question posted in 
If I have a .gitlab-ci.yml file like:
image: node:latest
test:
script:
- npm install
This runs fine – but if I run docker run --rm -it node:latest, it drops me at a node shell, which doesn’t recognise npm:
$ docker run --rm -it node:latest
Welcome to Node.js v21.6.2.
Type ".help" for more information.
> npm install
npm install
npm should be run outside of the Node.js REPL, in your normal shell.
(Press Ctrl+D to exit.)
>
I thought GitLab used whatever shell the container presented – is it secretly doing something like passing /bin/bash or /bin/sh to the docker command to get a shell it can run npm, etc. on?
2
Answers
The image entrypoint is just set to start a node shell.
Yes.
https://docs.gitlab.com/ee/ci/docker/using_docker_images.html#where-scripts-are-executed
The
nodeimage is a little confusing in that it can interpret its command in two different ways. If you runthen it runs the script, as though you had run
node index.js. But if you give it a normal commandit just runs it. This behavior comes from the image’s entrypoint wrapper script: if the provided command isn’t an executable shell command, then
nodeis prepended to it.This also explains the default behavior from
docker run -i nodeyou show above: if the command is empty, then it’s not a shell command andnodeis prepended to it, so the effective main container command is justnodeand it launches the interactive REPL.I think of the "standard" path to run a command in a container as to
docker run ... the-commandin a new container. Especially if programs are invoking Docker, they don’t start an interactive container and then run commands inside it (this is mechanically a little tricky and definitely harder than just creating a container).