Docker Compose

What is docker compose?

  • docker compose is tool for defining and running complex applications with Docker.
  • With Compose, we define a multi-container application in a single file.
  • It allows you to spin your application up in a single command.
  • Orchestration between two containers are easy with docker compose.
  • Default file name for docker-compose is is docker-compose.yml.

Docker Compose works in the scope of a single host, where Kubernetes works on multi cluster environment.

Simple compose file

  • This is what a simple compose file looks like.
version: '3'                                       # 1    
services:                                          # 2
  myApp:                                             # 3
    image: amantuladhar/docker-kubernetes:v1-web     # 4
  • #1 specifies what version of compose API you want to use.
  • #2 is a root property. It includes list of all services (containers) compose will manage.
  • #3 is name of the service (container)
  • #4 specifies image you want to run.

If you want to build you app yourself you can find the app in Spring Simple Web branch compose-initial.

  • You noticed that in compose file containers are called services.
  • Compose can manage multiple services, but for now we are dealing with only one.
  • We defined the service called myApp which will run the image.

Build your image

  • If you want to build your own image instead of using one, you can do that easily too
version: '3'
services:
  myApp:
    build:                     # 1  
      context: .               # 2
      dockerfile: Dockerfile   # 3
  • #1 build tag will let compose know that you want to build your image.
  • #2 context defines where your docker file are stored.
  • #3 Dockerfile takes the file name for Dockerfile. If the file name is Dockerfile you don't seed to specify the property.
  • You use docker-compose build to build your image. (docker compose build in the latest version)
  • If you make any changes to Dockerfile you need to explicitly build the image again.

Any docker compose command can now be used without - i.e as part of docker command

Running services

  • To run the services defined in compose file is super easy.
  • You run any number of services defined inside compose file with single command.
  • i.e docker-compose up. On latest docker for desktop installation you can just docker compose up.
  • If you want to run it in background add -d option.
  • If you run the app right now, it will run but it won't be accessible from our host yet.
  • We need to publish ports first in order to access the app.

Stopping services

  • Starting the services were easy. How about stopping them?
  • It is super easy as well. docker-compose stop. (docker compose stop in new version).
  • It will stop all running services at once.