Docker compose

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This is a study note from a tutorial video in YouTube: https://www.youtube.com/watch?v=fqMOX6JJhGo&t=4723s

Docker compose is used to run several differences services in one .yml file. 

 docker run WeibotopHistory 
 docker run mariadb 

docker-compose.yml
services:
    web:
        image: "WeibotopHistory"
    database:
        image: "mariadb"

Use "docker-compose" command to bring up all the application stacks in yml files.

 docker-compose up 

How to compose yml files?

To explain how to compose the yml files, we use the voting app example. The structure of voting app is like below:


These connections between difference services can be described using "run --link" command like below:
 docker run -d --name=redis redis 
 docker run -d --name=db postgres:9.4 
 docker run -d --name=vote -p 5000:80 --link redis:redis voting-app 
 docker run -d --name=result -p 5001:80 --link db:db result-app 
 docker run -d --name=worker --link db:db --link redis:redis worker 

Above commands can be described in yml file like below:

docker-compose.yml

redis: # This is the name of container, it is
# corresponding to "--name" in "run" command
image: redis # This is the image name
db:
image: postgres:9.4
vote:
image: voting-app
ports: # This is corresponding to "-p" in "run" command
- 5000:80
links: # This is corresponding to "--link" in "run" command
- redis
result:
image: result
ports:
- 5001:80
links:
- db
worker:
image: worker
links:
- redis
- db

However if some of the images have not been built yet, you can use "build" keywords instead of "image" to build and run. For example, since the voting-app, result app, and worker app are written by developer, they may not be built into images yet. Then we can modify above yml file to build the images.

redis:
image: redis
db:
image: postgres:9.4
vote:
build: ./vote # Here will build the image with directory "vote"
ports:
- 5000:80
links:
- redis
result:
build: ./result
ports:
- 5001:80
links:
- db
worker:
build: ./worker
links:
- redis
- db

Above format is for yml version 1.

In version 2, there are some differences:

  1. All the containers need to be defined in "services" section;
  2. If you need dependencies, you can use "depends_on" attribute to specify the services that need to be run before this service;
For example, the above yml can be modified in version 2 like below:

version: '2' # Here needs to specify the version using string
services: # All services need to be put under "services"
    redis:
    image: redis
    db:
    image: postgres:9.4
    vote:
    image: voting-app
    ports:
    - 5000:80
    depends_on: # Here to tell to run redis before run this
    - redis
    result:
    image: result
    ports:
    - 5001:80
    depends_on:
    - db
    worker:
    image: worker
    depends_on:
    - redis
    - db

Version 3 is similar to version 2. However some tags are removed and simplified.

Networking in docker compose

Let's use an example directly. 


If you want to create a network structure like above, you need to add"networks" tag in the yml files.

version: 2
services:
    redis:
    image: redis
        networks: # Here needs to specify the network you want
            - back-end # to use from the networks defined
    db:
    image: postgres:9.4
        networks:
            - back-end
    vote:
    image: voting-app
    ports:
    - 5000:80
    depends_on:
    - redis
        networks:
            - front-end
            - back-end
    result:
    image: result
    ports:
    - 5001:80
    depends_on:
    - db
        networks:
            - front-end
            - back-end
    worker:
    image: worker
    depends_on:
    - redis
    - db
        networks:
            - back-end
networks: # Here to define the networks
    front-end:
    back-end:



Reference: https://www.youtube.com/watch?v=fqMOX6JJhGo&t=4723s

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