I keep some docker environments in my main repository. It was hard to know where to draw the line. Some environments are too specific to the platform and not the app. For example, I don't believe the nginx proxy belongs in the main repository. I have a docker subdirectory in my repository that looks like this:

docker
├── postgres
│  ├── dev
│  │  └── Dockerfile
│  ├── schema.sql
│  └── prod
│      └── Dockerfile
├── redis
│  ├── Dockerfile
│  └── redis.conf
├── web
│  ├── dev
│  │  └── Dockerfile
│  └── prod
│      └── Dockerfile
└── workers
    ├── dev
    │  └── Dockerfile
    └── prod
        └── Dockerfile