Environment variable using docker-compose is always null

Questions / Help
,
1

How to use environment variables with docker without using phoenix?

With Phoenix it works but with only elixir is always null.

2

It works the same. Just make sure you’re not fetching the ENV variables in config/config.exs or config/prod.exs - those are evaluated at build time. Either use config/runtime.exs or read in the app.

1 Like
3

Yeah, I’m reading on the app using System.get_env(“NameOfEnv”) but for some reason they’re always nil.

I read in somewhere that it worked with Phoenix because they handle env variables in a different way

4

In a directory with a file test.exs containing:

IO.inspect(System.get_env("MY_VAR"), label: :env)

run

$ docker run -e MY_VAR=Hello -v $(pwd):/ws -w /ws -it --rm elixir:1.11.4 elixir test.exs
env: "Hello"

does that work?

5

Hello again Sebb, thanks for the help.

I’m using

mix run

To start the application and running

System.get_env("MY_VAR")

Inside a file being “supervised” by a Supervisor, would this change anything?

I’ll test the code you’ve sent

6

Running in a supervisor does not affect the environment you see. But running in docker does.

If you see the variable in the shell you run the application in - try:

echo $MY_VAR

Sytem.get_env will also see it.

7

Really weird thing is happening… With docker run -e […ENVS] it does work perfectly, but using docker-compose it doesn’t.

I attached to the container after started with docker compose and executed

echo $MY_VAR

in the shell and it printed with success, but for some reason when running with docker-compose and trying to System.get_env(“MY_VAR”) it’s null

8

This is my Dockerfile

FROM elixir:1.11-slim
RUN mkdir /app
COPY . /app
WORKDIR /app

# Install hex
RUN mix local.hex --force

#Install rebar
RUN mix local.rebar --force

#Get dependencies
RUN mix deps.get

#Run
RUN mix

This is my docker-compose.yml

version: "3.2"

services:
  checker:
    build:
      context: .
    environment:
      MY_VAR: "hello" 
    restart: on-failure

Mix.exs:

defmodule StockAlert.MixProject do
  use Mix.Project

  def project do
    [
      app: :stock_alert,
      version: "0.1.0",
      elixir: "~> 1.11.0",
      deps: deps()
    ]
  end

  # Configuration for the OTP application.
  #
  # Type `mix help compile.app` for more information.
  def application do
    [
      mod: {StockAlert.Application, []},
      extra_applications: [:elastix,:lager, :logger, :runtime_tools]
    ]
  end

  # Specifies your project dependencies.
  #
  # Type `mix help deps` for examples and options.
  defp deps do
    [
      {:elastix, "~> 0.10.0"},
      {:gettext, "~> 0.11"},
      {:jason, "~> 1.0"},
      {:websockex, "~> 0.4.2"},
      {:poison, "~> 3.1"},
      {:amqp, "~> 2.1"},
      {:json, "~> 1.4"}
    ]
  end
end

StockAlert.Application

defmodule StockAlert.Application do
  # See https://hexdocs.pm/elixir/Application.html
  # for more information on OTP Applications
  @moduledoc false

  use Application
  require Logger

  @registry :workers_registry

  def start(_type, _args) do
    mvar = System.get_env("MY_VAR")
    Logger.info "MY_VAR-> #{mvar}"
  end

  def registry(), do: @registry
end
9

And the log:

#12 97.50 Generated stock_alert app
#12 98.42 [info] MY_VAR ->
10

Not sure if this is the root of the issue, but this should be mix run.

12

Tryed with mix run but no luck

13 
web:
  environment:
    - DEBUG=1
1 Like
15

This one was tricky… Found the answer in docker-compose build environment variable - Stack Overflow

As the mix run is running on the Dockerfile, the environment section of docker-compose won’t work, so I had to use the args section on the docker-compose

version: "3.2"

services:
  checker:
    build:
      context: .
      args:
        - MY_VAR=hello
    restart: on-failure

And also declare the arg in the dockerfile

FROM elixir:1.11-slim
RUN mkdir /app
COPY . /app
WORKDIR /app

ARG MY_VAR
ENV MY_VAR $MY_VAR


# Install hex
RUN mix local.hex --force

#Install rebar
RUN mix local.rebar --force

#Get dependencies
RUN mix deps.get

RUN mix run

Thank you all for your help

19

This runs mix during build time of the container. At that point in time docker-compose has not yet set the environment.

You want to use CMD or ENTRYPOINT depending on your exact needs.

2 Likes
20

Yeah, this is the best answer, with it I don’t even need to use the args on docker-compose.

Thank you!