Docker compose tips

Using environment variables with env_file

For example:

Content of docker-compose.yml file:

version: "3"
services:
  busybox:
    image: "nginx:alpine"
    env_file:
      - example.env

Content of example.env file:

REDIS_HOST=localhost

Now we can using command docker exec example-env-docker-compose env to list all the environment variables

Example output:

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=116525becba5
REDIS_HOST=localhost
NGINX_VERSION=1.17.10
NJS_VERSION=0.3.9
PKG_RELEASE=1
HOME=/root

Here we are using env_file, there are some rules:

• An environment file named .env placed in the folder where the docker-compose command is executed
• Compose expects each line in an env file to be in VAR=VAL format.
• Comment line start with #, blank lines are ignored
• There is no special handling of quotation marks.