Docker Deep Dive: Advanced Techniques/

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Compose Files

Compose Files

Examine a sample Docker Compose YAML file.

We'll cover the following...

Compose uses YAML files to define microservices applications. We call them Compose files, and Compose expects you to name them compose.yaml or compose.yml. However, you can use the -f flag with the docker compose command to specify files with arbitrary names.

Docker Compose file for a multi-service application

Here is the Compose file we’ll be using. It’s called compose.yaml and is in the multi-container folder.

services:                     <<---- Microservices are defined in the "services" block

  web-fe:                     <<---- This block defines the web front-end microservice

    deploy:

      replicas: 1

    build: .

    command: python app.py

    ports:

      - target: 8080

        published: 5001

    networks:

      - counter-net

    volumes:

      - type: volume

        source: counter-vol

        target: /app

  redis:                      <<---- This block defines the Redis back-end microservice

    deploy:

      replicas: 1

    image: "redis:alpine"

    networks:

      counter-net:

networks:                     <<---- Networks are defined in this block

  counter-net:                

volumes:                      <<---- Volumes are defined in this block

  counter-vol:

The first thing to note is that the file has three top-level keys with a block of code beneath each:

  • services
  • networks
  • volumes

More top-level keys exist, but this app only uses the three in the list.

Let’s have a closer look at each.

Defining the web-fe service

The top-level services key is mandatory and is where you define application microservices. This app has two microservices called ...