Management of multiple containers

Usage of docker compose

Introduction of docker compose#

• Docker compose helps us manage multiple containers with a file.
  • Define a network
  • Define containers
  • For each container, it defines their images, environments, ports and so on.

Docker network configuration#

Network information#

• Setting the name of docker network
  • I set the name to dev-net.
• IP range of devnet was set to 192.168.100.0/24.
  • Namely, all of containers in dev-net network have 192.168.100.x IP address.
  • The above expression is called by CIDR which will be dealt in network section.

Creating a docker network#

• Generating a docker network with using network configuration described in Network information section.
  • It can be automatically generated by docker compose, but I will describe how you can create the docker network in manual.
  • I recommend that you manually create the network rather than automatic creation for Mac OS, I will describe why I recommend it in docker virtual private network(VPN) section.

docker network create --attachable --subnet 192.168.100.0/24 devnet

Docker container configuration#

• In this phase, I describe container information I need to configure.

Image collection#

• Choose docker images which you want to use.

Configuring container information#

Setting container names#

• Setting names for each container.

Setting environment variables#

• Some containers require environment variables.
  • mongodb container needs some environment variables.

Setting container ports#

• We can bind containers' ports to host machine’s ports.
• There are two ways to have access to guest containers from host machine.
  1. Direct access to container’s IP.
     • Basically, it can’t be used on Mac OS.
  2. Binding container ports to host machine.
     • Access to bound ports to localhost.

Setting volume mounts#

• Mounting Some path from host to container.
  • Assume that PROJECT_ROOT is /home/hackartist/data/greeting-server.

Docker compose configuration#

Writing docker-compose.yaml file#

• Composing dockers with Docker container configuration.
  • In networks section, I described the network name which has been manually created.
    • The containers in the network have a predefined subnet.
  • Describing containers' information in services section.
    • services is composed of mongodb and greeting-server.
      • The services' names of each container are used for containers' aliases in the composed network.
      • These aliases make each container able to access to other containers with the aliases as domain names.
    • restart section describes restart policy which makes containers are automatically restarted.
    • Other configurations related to the containers should be described in ports, environment and volumes sections.
    • working_dir denotes the location which the container is started in.
    • command describes starting command when the container is started.
      • greeting-server runs go run main.go command when it starts.

version: "3.8"

networks:
  default:
    external:
      name: devnet

services:
  mongodb:
    image: mongo:4
    container_name: mongodb
    restart: always
    ports:
      - 27017:27017
    environment:
      - MONGO_INITDB_ROOT_USERNAME: root
      - MONGO_INITDB_ROOT_PASSWORD: root
    volumes:
      - $PROJECT_ROOT/.build/data:/data/db
  greeting-server:
    image: golang:1.15
    container_name: greeting-server
    restart: always
    ports:
      - 3000:3000
    volumes:
      - $PROJECT_ROOT:/workdir
    working_dir: /workdir
    command: go run main.go

Running docker compose#

• Using a configuration file written in Writing docker-compose.yaml file section.
  • The configuration file passes an environmental variable, PROJECT_ROOT.
  • -f flag describes a configuration filename of docker compose.
    • docker-compose.yaml is a default configuration name, so it can be omitted.
  • -p flag describes a name of a docker stack which the container belongs to. It could make us easy to manage the containers.
  • up command composes dockers.
    • -d flag indicates that it should be run as background without attaching I/O.
    • If the only mongodb should be ran, ... up -d mongodb could be executed.

PROJECT_ROOT=/home/hackartist/data/greeting-server \
            docker-compose -f docker-compose.yaml -p greeting-server up -d

Shutting down the docker compose#

• down command removes all containers and network created by the docker compose.
  • If some containers would be orphans due to renaming or something else, --remove-orphans flag makes them removed.

PROJECT_ROOT=/home/hackartist/data/greeting-server \
            docker-compose -f docker-compose.yaml -p greeting-server down --remove-orphans