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Docker Compose Cheat Sheet

CLI

 docker-compose up           # start docker-compose.yml from current dir
 docker-compose down

Defining Dependencies

You MUST use a wait wrapper to ensure the readiness of the dependency. Otherwise the webapp container would start once the DB container is running, and not when the DB port is reachable.

 services:
   webapp:
     depends_on:
     - db
     command: ["./wait-for-it.sh", "db:5432", "--", "start_webapp"]
     [...]
   db:
     [...]

Custom Build Context

 services:
   webapp:
     build:
       context: ./webapp
       dockerfile: Dockerfile.webapp
       args:
         buildno: 1

Custom Network Config

Examples from compose documentation

Network

To assign a network a fixed CIDR range

networks:
  app_net:                                   # <-- any name goes here
    driver: bridge
    enable_ipv6: true
    ipam:
      driver: default
      config:
        - subnet: 172.16.238.0/24
          gateway: 172.16.238.1
        - subnet: 2001:3984:3989::/64        
          gateway: 2001:3984:3989::1

To make a service use it

service:
  my_app:
    [...]
    networks:
      - app_net

Service

To assign a service a fixed IP

services:
  my_app:
    image: busybox
    command: ifconfig
    networks:
      app_net:
        ipv4_address: 172.16.238.10
        ipv6_address: 2001:3984:3989::10

Mounting Volumes

services:
  my_app:
    volumes:
    # Actual volume mounts
    - vol1:/db
    - vol2:/mnt/vol2
    - vol3:/mnt/nfs
    
    # Bind mounts
    - src/tests:/opt/app/tests
    - /etc/ssl/certs/myCA.crt:/etc/ssl/certs/myCA.crt
            
volumes:
  vol1:                  # Auto-create volume
  vol2:
    external: true       # No auto-create volume, create with `docker volume create` manually
  vol3:
    driver: local        # NFS mounted volume
    driver_opts:
     type: "nfs"
     o: "addr=10.40.0.199,nolock,soft,rw"
     device: ":/docker/example"

Secrets

services:
  my_app:
    [...]
    secrets:
    - source: KEY1
      target: /opt/app/key.pem
      
 secrets:
   KEY1:
     file: secrets/key1.pem

Health Checking

services:
  webapp:
    [...]
    healthcheck:
       test: >
         curl --noproxy "*" -v -f -s http://127.0.0.1:8080/webapp
       interval: 15s
       timeout: 5s
       retries: 20
       start_period: 30s

Restarting Services

Old style:

 services:
   webapp:
      restart: <no|always|on-failure|unless-stopped>

new style:

 services:
   webapp:
     [...]
     deploy:
       restart_policy:
         condition: on-failure
         delay: 5s
         max_attempts: 3
         window: 120s

Setup Troubleshooting

Couldn’t connect to Docker daemon at http+docker://localhost - is it running?

Ensure systemd unit is configured correctly and has TCP socket configured. If not edit with sudo systemctl edit docker.service and provide

[Service]
ExecStart=/usr/bin/dockerd -H fd:// -H tcp://127.0.0.1:2375

Also set env var DOCKER_HOST

export DOCKER_HOST=127.0.0.1:2375