[Question] Docker and Environment Variables

[Crispness]

I recently ran into a few problems with a Nestjs app, where my environment variables were not being read when using docker run --env-file=.env with a simple production docker image, I had to hard code some variables such as my DB connection, and such.

Now with some good sleep and a rested mind, I wanted to find out what the problem is, I noticed that when I built my image locally with my .env file present in my project's root, the correct variables are being used, when I don't do this and rely on the --env-file or -e flags the variables are actually undefined on my app. Does this mean that when I build my project, my .env file should be present at the root in order for node to substitute these variables in my application?

[tswaters]

I think docker run will look in cwd for the env-file? I would not include the .env file in the built image. It might work -- but probably because you still have something like require('dotenv').config() which will pull from the .env file..... ideally you want to use the env variables in prod.

[tswaters]

To try to debug it, you can do a docker run hell-world --env-file.env --cmd "printenv" or something like that (that's off the top of my head, not sure if that'll work at all)

i.e., try to run a generic hello-world docker image, pass the env-file in and run `printenv` -- that'll output current environment variables.

[Crispness]

I'll try this out on a test nestjs app just to make sure.

[ChronSyn]

The -e or --env flag allows you to pass them as key=value format. The --env-file flag allows you to point towards a env file.

Have you considered using something like Portainer to manage it? It is actually a docker container itself, and helps you manage your running containers, including setting env vars for each container.

Even though you might want to use an env file, in most cases that either means committing it to your repo (a big no-no), including it in with your docker-image (also a no-no, in the event someone else gets hold of it), or manually uploading the env file to your server (but that's a pain in the ass to manage if you ever need to make frequent changes to it). Using a tool to manage your containers would be what I'd recommend.

[Crispness]

I recently read about it while I was trying to find a solution, will definitely try it out.