Workaround to docker run "--env-file" supplied file not being evaluated as expected

Question

My current setup for running a docker container is on the lines of this:

1. I've got a main.env file:

# Main
export PRIVATE_IP=\`echo localhost\`
export MONGODB_HOST="$PRIVATE_IP"
export MONGODB_URL="mongodb://$MONGODB_HOST:27017/development"

2. In my service file (upstart), I source this file . /path/to/main.env

3. I then call docker run with multiple -e for each of the environment variables I want inside of the container. In this case I would call something like: docker run -e MONGODB_URL=$MONGODB_URL ubuntu bash

4. I would then expect MONGODB_URL inside of the container to equal mongodb://localhost:27017/development. Notice that in reality echo localhost is replaced by a curl to amazon's api for an actual PRIVATE_IP.

This becomes a bit unwieldy when you start having more and more environment variables you need to give your container. There is a fine point to see here which is that the environment variables need to be resolved at run time, such as with a call to curl or by referring to other env variables.

The solution I was hoping to use is:

1. calling docker run with an --env-file parameter such as this:

# Main
PRIVATE_IP=\`echo localhost\`
MONGODB_HOST="$PRIVATE_IP"
MONGODB_URL="mongodb://$MONGODB_HOST:27017/development"

2. Then my docker run command would be significantly shortened to docker run --env-file=/path/to/main.env ubuntu bash (keep in mind usually I've got around 12-15 environment variables.

This is where I hit my problem which is that inside the container none of the variables resolve as expected. Instead I end up with:

• PRIVATE_IP=`echo localhost`
• MONGODB_HOST="$PRIVATE_IP"
• MONGODB_URL="mongodb://$MONGODB_HOST:27017/development"

I could circumvent this by doing the following:

1. Sourcing the main.env file.
2. Creating a file containing just the names of the variables I want (meaning docker would search for them in the environment).
3. Then calling docker run with this file as an argument to --env-file. This would work but would mean I would need to maintain two files instead of one, and really wouldn't be that big of an improvement of the current situation.

What I would prefer is to have the variables resolve as expected.

The closest question to mine that I could find is: 12factor config approach with Docker

Answer 1

• Ceate a .env file

 example: test=123 val=Guru

• Execute command

docker run -it --env-file=.env bash

• Inside the bash verify using

echo $test (should print 123)