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Seeing port mappings

(David J. Malan) #1

Hi all,

We use a command-line tool, cli50, that essentially makes it easier to spawn a Linux container on a host and mount one’s $PWD inside of it. Per, it essentially does this:

docker pull cs50/cli
docker run --publish-all --volume "$PWD":/home/ubuntu/workspace --workdir /home/ubuntu/workspace cs50/cli bash --login

(Omitted from the above are some customization features.)

The tool’s Dockerfile, meanwhile, per, exposes 3 ports:8080, 8081, and 8082. We’d like the user to know to what ports those 3 have been pseudorandomly mapped (per --publish-all), without hardcoding a mapping (so that you can run multiple containers on multiple trios of ports). We initially tried, in a nutshell

docker run --detach cs50/cli bash --login # to run container in background
docker port # to figure out port mapping
docker attach # to re-attach to container

but that approach seemed suboptimal, since when we re-attach to the container, the user doesn’t see a bash prompt (since it printed when the container was background), so it’s non-obvious that they have an interactive terminal at that point.

As a workaround, we’ve since started doing, in a nutshell:

docker run --detach cs50/cli sleep infinity # to run container in background
docker port # to figure out port mapping
docker exec --interactive --tty bash --login # to start bash in container

But a side effect is that, when you exit out of bash, sleep is still running in the background, so the container doesn’t automatically stop.

Is there a more elegant solution here that would yield the same UX, a la the below?

$ cli50
latest: Pulling from cs50/cli
Digest: sha256:7ba11681b4eb4eef363a94f38ba23973b32b8c5bcc8bf212bf5b57127ee156b8
Status: Image is up to date for cs50/cli:latest
8080/tcp ->
8081/tcp ->
8082/tcp ->
This is CS50 CLI.
root@9183ff478d12:/home/ubuntu/workspace #

Many thanks!


(Think) #2

is --net=host an option? it’s just an utility script, so shouldn’t be that much of an issue?
then you wouldn’t need the port mapping at all.

(David J. Malan) #3

Hm, I think the catch there would be that we couldn’t run multiple cs50/cli containers at a time, if each wants to use 8080, 8081, and/or 8082? (We could manually run the port-using services in each container on randomly chosen ports, but that would just push the pseudorandomness on to the user?)


(Think) #4

But when you use --net=host, you would not need the infinity-sleep anymore….so maybe this problem is then gone?
BTW: You anyway got problems to figuring out once there are multiple cs50/cli-containers, whose port mappings you should read and use.

(Sam) #5

so, 1st… what ports…

docker inspect on the containers will show you what host ports have been mapped to what container ports.

and for the name, you should use --name container{number} or something…

(Think) #6

if --net=host is no option for you, then just use your sleep-inspect way. :slight_smile: