# Docker-compose
Create a collection of interconnected containers, networks, and volumes with a single command.

## CLI
- `docker-compose up`: create all containers, networks and volumes described in our docker-compose file
- `docker-compose up -d`: same as above, but run containers in detached mode
- `docker-compose -f <filename> up`: create containers based on a different docker-compose file
- `docker-compose down`: remove all containers and networks
- `docker-compose down -v`: remove all containers, networks, and volumes

## `docker-compose.yml` file
The docker-compose tool uses files written in a data-serialization language called YAML (extension is `.yml`)

At the top level of each file, include the version of docker-compose, then you can list services (containers), plus any volumes or networks if necessary.

version: '3.8'

services:
  # any services go here
networks:
  # networks go here
volumes:
  # volumes

### services
The next level down will be the name of the service/container.

Useful keywords

| Keyword | Purpose |
|--------- |---------|
|`build` | specify where to find the Dockerfile to build image |
|`image` | multipurpose: can name a newly built image, or specify name of image to build from |
|`volumes` | specify volumes or bind mounts to connect to image |
|`networks` | will connect container to specified networks |
|`environment` | add environment variables |
|`ports` | publish ports |

services:
#   build: .
  service_name:
    build:
        context: ./folder_with_dockerfile
        dockerfile: Dockerfile-alternate.Dockerfile
    image: whatevername # like the -t flag when you are building your image
    # if you don't have a build command, Docker will try to build from an existing image with that name
    volumes: 
        # with a named volume - also list name under top-level volumes
        - volume_name:/path/to/volume/on/container
        # for bind mounts
        - ./path/locally:/path/to/bind/mount/on/container
    # by default, docker-compose will create a single network for all containers
    networks:
        - network_name
    environment:
      DATABASE_URL: postgresql://username:password/localhost
      ANOTHER_VARIABLE: more-stuff
    ports:
      # <external port>:<internal port>
      -8000:80
  second_service_name:
    #... all the keywords for this service

### volumes
If you include any named volumes, list their names under the top-level "volumes" key.

Anonymous volumes and bind mounts don't need to be listed.

volumes:
  some_named_volume:
  another_named_volume:

### networks
If you don't specify a network, all the containers in the docker-compose file will be put onto one network together.

If you want multiple networks, specify all the names under the top-level volumes key.

networks:
  network_name:
  second_network_name: