Postgres without username or pass, but working ok?

Troubleshooting
1

I was getting ready to make a backup of the postgres database before updating MM to v8 (docker), and I realized that the docker.yml file doesn’t have a USERNAME, PASSWORD, or DB for postgres. Probably that was never set, but I have been running MM for some time without any major issues, which I don’t quite get how that is possible without credentials for postgres.

this is the contents of my docker.yml

services:
  postgres:
    image: postgres:${POSTGRES_IMAGE_TAG}
    restart: ${RESTART_POLICY}
    security_opt:
      - no-new-privileges:true
    pids_limit: 100
    read_only: true
    tmpfs:
      - /tmp
      - /var/run/postgresql
    volumes:
      - ${POSTGRES_DATA_PATH}:/var/lib/postgresql/data
    environment:
      # timezone inside container
      - TZ

      # necessary Postgres options/variables
      - POSTGRES_USER
      - POSTGRES_PASSWORD
      - POSTGRES_DB

  mattermost:
    depends_on:
      - postgres
    image: mattermost/${MATTERMOST_IMAGE}:${MATTERMOST_IMAGE_TAG}
    restart: ${RESTART_POLICY}
    security_opt:
      - no-new-privileges:true
    pids_limit: 200
    read_only: ${MATTERMOST_CONTAINER_READONLY}
    tmpfs:
      - /tmp
    volumes:
      - ${MATTERMOST_CONFIG_PATH}:/mattermost/config:rw
      - ${MATTERMOST_DATA_PATH}:/mattermost/data:rw
      - ${MATTERMOST_LOGS_PATH}:/mattermost/logs:rw
      - ${MATTERMOST_PLUGINS_PATH}:/mattermost/plugins:rw
      - ${MATTERMOST_CLIENT_PLUGINS_PATH}:/mattermost/client/plugins:rw
      - ${MATTERMOST_BLEVE_INDEXES_PATH}:/mattermost/bleve-indexes:rw
    environment:
      # timezone inside container
      - TZ
      # necessary Mattermost options/variables (see env.example)
      - MM_SQLSETTINGS_DRIVERNAME
      - MM_SQLSETTINGS_DATASOURCE

      # necessary for bleve
      - MM_BLEVESETTINGS_INDEXDIR

      # additional settings
      - MM_SERVICESETTINGS_SITEURL

However, the volumes/app/mattermost/config/config.json has the following line, could they be the postgres credentials set by dafult?

"SqlSettings": {
        "DriverName": "postgres",
        "DataSource": "postgres://mmuser:mostest@localhost/mattermost_test?sslmode=disable\u0026connect_timeout=10\u0026binary_parameters=yes",

And based on this, are these the credentials for postgres that I need to use to make a backup?
User: mmuser
Pass: mostest
Db: mattermost_test

How could I go about assigning a new name, password, and db to my docker MM (without losing the data in the above db)?

2

I just figured it out. I forgot that there is a .env file that sets those variables.