docker-compose.yml demonstration 2019.10.09

readme-docker-compose_demonstration.md

Our Dockerfile:

FROM alpine
ADD script.sh /script.sh
CMD ["/bin/sh", "/script.sh"]

Our script.sh

#!/bin/sh
echo "Message: ${VAR_MESSAGE:-nothing_defined}"

When we build our image and run a container from that image without any variables set, we will expect Message: nothing_defined

$ docker build -f Dockerfile -t local:v1 .
$ docker run -it local:v1
Message: nothing_defined

When we pass the environment variable, we will see it in our output:

$ docker run -it -e VAR_MESSAGE=hello_world local:v1
Message: hello_world

Using Docker Compose

Our docker-compose.yml

version: "3.7"
services:
  hello:
    build:
      context: .
      dockerfile: Dockerfile
    environment:
      - VAR_MESSAGE=hello_world
    networks:
      - hello

networks:
  hello:

Building:

$ docker-compose build

Running:

$ docker-compose up                                                                                                                                    1 ↵
Creating network "aa_hello" with the default driver
Message: hello_world

Docker Compose with 2 Services

Let's take a producer and consumer setup, where we will have 2 services defined in our compose, where they will work together.

We will have a shared volume and one container will write to the shared volume and the other container will read from that volume.

We also instruct our compose to only let the consumer container run after the producer has started.

Our Dockerfile for our producer: Dockerfile.producer

FROM alpine
ADD script.sh /script.sh
CMD ["/bin/sh", "/script.sh"]

Our Dockerfile for our consumer: Dockerfile.consumer

FROM alpine
CMD echo "reading from file -> $(cat /data/file.txt)"

The script that the producer will run:

#!/bin/sh
echo "writing to disk"
echo "Message: ${VAR_MESSAGE:-nothing_defined}" > /data/file.txt

Our docker-compose.yml

version: "3.7"
services:
  producer:
    build:
      context: .
      dockerfile: Dockerfile.producer
    environment:
      - VAR_MESSAGE=hello_world
    volumes:
      - shared_vol:/data
    networks:
      - hello

  consumer:
    build:
      context: .
      dockerfile: Dockerfile.consumer
    volumes:
      - shared_vol:/data
    depends_on:
      - producer
    networks:
      - hello

volumes:
  shared_vol:
    driver: local

networks:
  hello:

Building and running our containers:

$ docker-compose build
$ docker-compose up
Creating network "aa_hello" with the default driver
Creating volume "aa_shared_vol" with local driver
Creating aa_producer_1 ... done
Creating aa_consumer_1 ... done

Attaching to aa_producer_1, aa_consumer_1
producer_1  | writing to disk
consumer_1  | reading from file -> Message: hello_world

aa_producer_1 exited with code 0
aa_consumer_1 exited with code 0