4. Docker compose

Contents

Note: Docker compose can be used with a single container, in order to simplify (and document) a complex command line.

Commands

docker-compose up

-d detached
--build build containers before

docker-compose down

docker-compose ps
→ to be executed in the directory of a docker-compose.yml file

docker-compose.yml basic example

version: "3"

services:

  # very basic setup
  web:
    image: steveltn/https-portal:1
    environment:
      ...
    ports:
      - 80:80
      - 443:443

  # not using an image, but a docker file located into ./service1
  # wa have a restart policy as well
  myservice1:
    build: ./service1
    restart: always

  # custom Dockerfile name
  myservice2:
    build:
      context: ./service2
      dockerfile: Dockerfile.service2
    restart: always

  # custom CMD 
  myservice3:
    image: bash
    command: echo hello world

restart policies

'no' → don't forget quotes for this value!
always
on-failure (based on exit code)
unless-stopped

Environment

There are two syntaxes

KEY=value → make this env variable available at runtime with this value
KEY → make this env variable available at runtime. Find the value in the host env variable.

depends_on

Express dependency between services. Service dependencies cause the following behaviors:

docker-compose up starts services in dependency order. In the following example, db and redis are started before web.
docker-compose up SERVICE automatically includes SERVICE’s dependencies. In the example below, docker-compose up web also creates and starts db and redis.
docker-compose stop stops services in dependency order. In the following example, web is stopped before db and redis.

Simple example:

version: "3.8"
services:
  web:
    build: .
    depends_on:
      - db
      - redis
  redis:
    image: redis
  db:
    image: postgres