Generic Environment Substitution Solution

[amouat]

Which image/versions are related to this issue/feature request?

All images that have configuration options, especially those that use a configuration file.

Issue/Feature description

Many container images from other providers support env var substitution - that is you can docker something like docker run -e MYPORT=5000 myimage to configure options on the image that would normal require editing and volume mounting a config file.

This is fairly simple to do with a shell script and envsbst (https://man7.org/linux/man-pages/man1/envsubst.1.html). But it's a little more difficult in a minimal container without pulling in a shell (which I really don't want to do). My suggestion is to create a small reusable binary that runs as an entrypoint and doees this for us. We could extend: https://github.com/wolfi-dev/container-entrypoint

[dlorenc]

+1 on doing this as a small rust/go binary!

[amouat]

The only thing that gives me pause is it's not very transparent; if it was a bash script it's a lot easier to see what's going on.

[imjasonh]

The only thing that gives me pause is it's not very transparent; if it was a bash script it's a lot easier to see what's going on.

I think a little static Go binary would be great, and not require a shell anymore.

Having to reimplement parts of some bash commands (like command) seems like it might be annoying, but ultimately being able to have the benefits of an entrypoint.sh without a shell seems valuable.

[leksmano]

would it be possible to support functionality similar to the templates described here: https://github.com/docker-library/docs/tree/master/nginx#using-environment-variables-in-nginx-configuration-new-in-119 ?

[vicious-dahlia]

Please add this feature, it's necessary for many practical uses of nginx.

[black-snow]

I currently use https://gitlab.com/black-snow/env-dump in some places. I could extend it if you tell me what you need.

[ericsmalling]

Just heard from another customer that relies on this feature for nginx

[ctr49]

How about using renvsubst instead of envsubst - this should be more aligned with the minimal container image approach.

[kevinneufeld]

We also rely on this feature, which is the primary reason we cannot use the chainguard image as is.

[smythp]

Thought I'd ask about the status of this feature since I'm updating the nginx README.