Docker Environment Variables

Environment variables can be set different ways in a Docker Compose yml file. These are set at run time when the container is started up, it is not encoded anywhere inside the image.

Specify a value

Set a variable at run time with a specified value from the Docker-compose.yml file like this:

variableName=value

Use a setting from the local environment

This will set a value from the local environment, for example the local computer environment setting:

variableName

How this would look in a Docker-Compose file:

version: '3'
services:
  redis:
    image: 'redis:latest'
  server:
    build:
      dockerfile: Dockerfile.dev
      context: ./server
    volumes:
      - /app/node_modules
      - ./server:/app
    environment:
      - REDS_HOST=redis
      - REDIS_PORT=6379

In this example we link the REDIS_HOST value directly to the redis service as defined in the same yml file.