Read JSON-file into environment variable with Docker Compose

Question

I've dockerized a Meteor-app with Meteord, and that works fine, my problem is that I want to pass some settings to the app.

Meteord does not start the app with a settings-file as one would usually do to give settings to an app (meteor --settings file.json). This is also possible to do with an environement variable called METEOR_SETTINGS.

As I want the webapp to run with other services, I'm using Docker Compose.

I have my settings.json-file that I want to be read in as a environment variable, so something like:

  environment:
   - METEOR_SETTINGS=$cat(settings.json)

This doesn't work though.

How can I make Docker compose dynamically create this environment variable based on a JSON-file?

Kevin Newman · Accepted Answer · 2020-04-25 05:14:54Z

8

An easy way to do this is to load the JSON file in to a local env var, then use that in your yaml file.

In docker-compose.yml

environment:
  METEOR_SETTINGS: ${METEOR_SETTINGS}

Load the settings file before invoking docker-compose:

❯ METEOR_SETTINGS=$(cat settings.json) docker-compose up

answered Apr 25, 2020 at 5:14

Kevin Newman

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Erik Dannenberg · Accepted Answer · 2016-04-18 00:24:19Z

5

Not possible without some trickery, depending on the amount of tweakable variables in settings.json:

If it's a lot of settings it's fairly easy to template the docker-compose.yml with a simple shell script that replaces a token in the template with the contents of settings.json, much like in your example. You also want to wrap the docker-compose call in that case. Simplified example:

docker-compose.yml.template:

environment:
 - METEOR_SETTINGS=##_METEOR_SETTINGS_##

dc.sh:

#!/bin/sh
# replace ##_METEOR_SETTINGS_## with contents of settings.json and output to docker-compose.yml
sed -e 's|##_METEOR_SETTINGS_##|'"$(cat ./settings.json)"'|' \
    "./docker-compose.yml.template" > "./docker-compose.yml"
# wrap docker-compose, passing all arguments
docker-compose "$@"

Put the 2 files into your project root, then chmod +x dc.sh to make the wrapper executable and call ./dc.sh -h.

If it's only a few settings you could handle the templating inside the container when its starting. Simply replace tokens placed in a prepared settings.json with ENV values passed to docker before starting Meteor. This allows you to just use the docker-compose ENV features to configure Meteor.

edited Apr 18, 2016 at 0:24

answered Apr 17, 2016 at 20:07

Erik Dannenberg

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4 Comments

Esso Over a year ago

Thanks! What do you mean by wrapping the docker-compose call, and could you provide an example of the templating technique with a shell script in your answer?

Erik Dannenberg Over a year ago

I updated the answer, untested but should get you going.

Esso Over a year ago

The only problem with this is that I found Meteor does not have access to environment variables built in, so you have to go via Node. My solution was to paste the JSON-settings into a METEOR_SETTINGS variable in an env-file, but I recommend adjusting this suggested scriped if one has many settings variables, so that the script creates the env-file for you.

Mehdi Charife Over a year ago

Unfortunately, this is not portable.

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