There's 4 images that you can find in `/build` directory:
-`bench`. It is used for development. [Learn more how to start development](../development/README.md).
-`nginx`. This image contains JS and CSS assets. Container using this image also routes incoming requests using [nginx](https://www.nginx.com).
-`socketio`. Container using this image processes realtime websocket requests using [Socket.IO](https://socket.io).
-`worker`. Multi-purpose Python backend. Runs [Werkzeug server](https://werkzeug.palletsprojects.com/en/2.0.x/) with [gunicorn](https://gunicorn.org), queues (via `bench worker`), or schedule (via `bench schedule`).
> `nginx`, `socketio` and `worker` images — everything we need to be able to run all processes that Frappe framework requires (take a look at [Bench Procfile reference](https://frappeframework.com/docs/v13/user/en/bench/resources/bench-procfile)). We follow [Docker best practices](https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#decouple-applications) and split these processes to different containers.
> ERPNext images don't have their own Dockerfiles. We use [multi-stage builds](https://docs.docker.com/develop/develop-images/multistage-build/) and [Docker Buildx](https://docs.docker.com/engine/reference/commandline/buildx/) to reuse as much things as possible and make our builds more efficient.
After building the images we have to run the containers. The best and simplest way to do this is to use [compose files](https://docs.docker.com/compose/compose-file/).
We have one main compose file, `compose.yaml`. Services described, networking, volumes are also handled there.
-`configurator`. Updates `common_site_config.json` so Frappe knows how to access db and redis. It is executed on every `docker-compose up` (and exited immediately). Other services start after this container exits successfully.
-`db`. Optional service that runs [MariaDB](https://mariadb.com) if you also use `overrides/compose.mariadb.yaml` or [Postgres](https://www.postgresql.org) if you also use `overrides/compose.postgres.yaml`.
-`redis`. Optional service that runs [Redis](https://redis.io) server with cache, [Socket.IO](https://socket.io) and queues data.
-`overrides/compose.erpnext.yaml`. Replaces all Frappe images with ERPNext ones. ERPNext images are built on top of Frappe ones, so it is safe to replace them.
-`overrides/compose.https.yaml`. Automatically sets up Let's Encrypt certificate and redirects all requests to directed to http, to https.
It is quite simple to run overrides. All we need to do is to specify compose files that should be used by docker-compose. For example, we want ERPNext:
```bash
# Point to main compose file (compose.yaml) and add one more.
ERPNext [release](https://github.com/frappe/frappe/releases). This variable is required if you use ERPNext override.
### `LETSENCRYPT_EMAIL`
Email that used to register https certificate. This one is required only if you use HTTPS override.
### `FRAPPE_SITE_NAME_HEADER`
This environment variable is not required. Default value is `$$host` which resolves site by host. For example, if your host is `example.com`, site's name should be `example.com`, or if host is `127.0.0.1` (local debugging), it should be `127.0.0.1` This variable allows to override described behavior. Let's say you create site named `mysite` and do want to access it by `127.0.0.1` host. Than you would set this variable to `mysite`.
There is other variables not mentioned here. They're somewhat internal and you don't have to worry about them except you want to change main compose file.
