# Docker Compose

> Markdown source of <https://docs.calebsargeant.com/computing/docker/compose/>.

- Why: configure relationships between containes

- Why: save our docker container run settings in easy-to-read file

- Why: create one-liner developer environment startups

- Comprised of 2 seperate but related things

  > 1.  YAML-formatted file that describes our solution options for:
  >
  >     > - containers
  >     > - networks
  >     > - volumes
  >
  > 2.  A CLI tool `docker-compose` used for local dev/test automation with those YAML files

## docker-compose.yml

- Compose YAML format has it's own versions: 1, 2, 2.1, 3, 3.1
- YAML file can be used with `docker-compose` command for local docker automation or...
- With `docker` directly in production with Swarm (as of v1.13)
- `docker-compose --help`
- `docker-compose.yml` is default filename, but any can be used with `docker-compose -f`

## docker-compose CLI

- CLI tool comes with Docker for WIndows/Mac, but separate download for Linux

- Not a production-grade tool but ideal for local development and test

- Two most common commands are

  > - `docker-compose up` - setup volumes/networks and start all containers
  > - `docker-compose down` - stop all containers and remove cont/vol/net

- If all your projects had a `Dockerfile` and `docker-compose.yml` then "new developer onboarding" would be:

  > - `git clone github.com/some/software`
  > - `docker-compose up`

## Use Compose to Build

- Compose can also build your custom images
- WIll build them with `docker-compose up` if not found in cache
- Also rebuild with `docker-compose build`
- Great for complex builds that have lots of vars or build args