Overview

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Docker container is a single solution process. In real world, we have to deal with multiple containers like, web server, proxy server, worker process, frontend, database server etc. We have to virtual networking, expose public ports and overall orchestrate each pieces. And this is exactly what docker-compose does for us.

With docker-compose we can orchestrate the services and spin them up in the local and test environment.

Docker compose consists of two separate but related things,

• Docker compose YML file, we used to define containers, networking and volumes.
• docker-compose CLI, a cli-tool used in the local dev or test environment to automate these YAML file to simplify our docker commands.

docker-compose.yml

• docker-compose.yml file solely responsible for automation in local dev or test environment. Although now it is possible to use docker compose as docker commands (Ex, v1.13 or latest can be used in Swarm).
• Default name for docker compose file is docker-compose.yml. We can use custom names and use it with -f flag.
• In yml file we can use indentation of 2 or 4 spaces

version : Each yml file has own version. If we do not specify the version, it is assumed the docker-compose.yml file is under v1. It is recommended to use at least v2.

services : Containers, same as docker run command.

servicename : A user friendly name of the container. Also used as DNS name under the virtual network.

image : Specify a image the container will build from. Can be redis, mysql etc.

command : Override the container start up command.

environment : Pass the container environment variables. For example, when we run a database container, we may pass the password through this environment.

volumes : Do the volume mapping like Named Volume or Bind Mounting.

A sample docker-compose.yml file can be as follows,

version: '3.1'

services:
  servicename:
    image:
    command:
    environment:
    volumes:
  servicename:

volumes:
network: