# docker-compose-m4

preprocess docker-compose.yml with m4

This is a simple script that preprocesses your docker-compose.yml file with the m4 preprocessor.

## Installation

```
# make install
```

## Usage

Let's say we have a docker-compose.yml file like following. We would like to store it in a git repository, but we don't want to show people the postgres password.

One option would be to use [secrets](https://docs.docker.com/compose/use-secrets/), but that won't work if one of the containers doesn't support reading the password from a file.
We would need a preprocessor for that.

`docker-compose.yml`
```yaml
version: '3'

services:
  db:
    image: postgres:15
    volumes:
      - ./data/postgres:/var/lib/postgresql/data
    restart: unless-stopped
    environment:
      - POSTGRES_USER=joplin
      - POSTGRES_DB=joplin
      - POSTGRES_PASSWORD=passwordpasswordpasswordpasswordpasswordpasswordpasswordpassword
  app:
    image: joplin/server:latest
    depends_on:
      - db
    ports:
      - "127.0.0.1:22300:22300"
    restart: unless-stopped
    environment:
      - APP_PORT=22300
      - APP_BASE_URL=https://joplin.example.com/
      - DB_CLIENT=pg
      - POSTGRES_CONNECTION_STRING=postgresql://joplin:passwordpasswordpasswordpasswordpasswordpasswordpasswordpassword@db/joplin?sslmode=disable
```

1. Let's rename `docker-compose.yml` to `docker-compose.yml.m4`

```
mv docker-compose.yml docker-compose.yml.m4
```

2. Move the password to a separate text file next to `docker-compose.yml.m4` and modify `docker-compose.yml.m4` to read the password from that file.

`pgpass.txt`
```
passwordpasswordpasswordpasswordpasswordpasswordpasswordpassword
```

We can use the `iinclude()` function from docker-compose-m4 to include a file and strip newlines.

`docker-compose.yml.m4`
```diff
version: '3'

services:
  db:
    image: postgres:15
    volumes:
      - ./data/postgres:/var/lib/postgresql/data
    restart: unless-stopped
    environment:
      - POSTGRES_USER=joplin
      - POSTGRES_DB=joplin
-      - POSTGRES_PASSWORD=passwordpasswordpasswordpasswordpasswordpasswordpasswordpassword
+      - POSTGRES_PASSWORD=iinclude(pgpass.txt)
  app:
    image: joplin/server:latest
    depends_on:
      - db
    ports:
      - "127.0.0.1:22300:22300"
    restart: unless-stopped
    environment:
      - APP_PORT=22300
      - APP_BASE_URL=https://joplin.example.com/
      - DB_CLIENT=pg
-      - POSTGRES_CONNECTION_STRING=postgresql://joplin:passwordpasswordpasswordpasswordpasswordpasswordpasswordpassword@db/joplin?sslmode=disable
+      - POSTGRES_CONNECTION_STRING=postgresql://joplin:iinclude(pgpass.txt)@db/joplin?sslmode=disable
```

Finally run the preprocessor to generate the docker-compose.yml file.
```
docker-compose-m4
```

`docker-compose.yml` is now created and ready to be used.

`docker-compose.yml`
```yaml
# DO NOT EDIT THIS FILE
# it has been autogenerated from docker-compose.yml.m4, edit that file instead and then run docker-compose-m4

version: '3'

services:
  db:
    image: postgres:15
    volumes:
      - ./data/postgres:/var/lib/postgresql/data
    restart: unless-stopped
    environment:
      - POSTGRES_USER=joplin
      - POSTGRES_DB=joplin
      - POSTGRES_PASSWORD=passwordpasswordpasswordpasswordpasswordpasswordpasswordpassword
  app:
    image: joplin/server:latest
    depends_on:
      - db
    ports:
      - "127.0.0.1:22300:22300"
    restart: unless-stopped
    environment:
      - APP_PORT=22300
      - APP_BASE_URL=https://joplin.example.com/
      - DB_CLIENT=pg
      - POSTGRES_CONNECTION_STRING=postgresql://joplin:passwordpasswordpasswordpasswordpasswordpasswordpasswordpassword@db/joplin?sslmode=disable
```