add guide for migrating database user to a non-superuser

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Marco Kundt 2021-04-12 10:30:42 +02:00
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## Migrating existing superuser to a less privileged user
Mattermost-docker used to use the initially created user while database initialization. This is being accomplished by using the
`POSTGRES_USER` environment variable of the PostgreSQL Docker image. While this is convinient because it requires less setup steps
it's best practice and desirable to us a less privileged user to connect to the database. The following steps should be safe and
executable while Mattermost is running.
**NOTE:** Commands with a **$** prefix denote those are executed as user, **#** as root and commands without a prefix are database commands.
We assume the database name is *mattermost* and the database user *mmuser*.
1. Find out the name or id of the PostgreSQL container
To get either the name or the id of the running PostgeSQL container we can use `$ sudo docker ps`.
2. Attaching to the database container
`$ sudo docker exec -it POSTGRES_CONTAINER_NAME/ID /bin/sh`
3. Connecting to the database
```
# psql DATABASE_NAME USERNAME
e.g.
# psql mattermost mmuser
```
4. Checking if the Mattermost user is a superuser
The following PostgreSQL command will print a list of the present users and its attributes.
```
\du
```
A possible output can look like the following:
```
List of roles
Role name | Attributes | Member of
-----------+------------------------------------------------------------+-----------
mmuser | Superuser, Create role, Create DB, Replication, Bypass RLS | {}
```
5. Creating a new `superuser` and changing existing role attributes
**ATTENTION:** It's strongly recommended to create a database prior alteration. This can be done by stopping the database
and backup the PostgreSQL data path at filesystem level and/or to use `pg_dumpall`. For this attach to the running PostgreSQL
container described in step 2 and execute:
```
pg_dump -U mmuser -d mattermost > /var/lib/postgresql/data/BACKUP_MATTERMOST.sql
```
This dumps your *mattermost* database to the mounted directory, specified in the docker-compose.yml file.
After your backup is done you can connect to the database (see step 3) and execute the following SQL queries:
```
CREATE ROLE superuser WITH BYPASSRLS REPLICATION CREATEDB CREATEROLE SUPERUSER LOGIN PASSWORD 'superuser_passwd';
ALTER DATABASE mattermost OWNER TO superuser;
ALTER DATABASE postgres OWNER TO superuser;
ALTER DATABASE template0 OWNER TO superuser;
ALTER DATABASE template1 OWNER TO superuser;
GRANT ALL PRIVILEGES ON DATABASE mattermost to mmuser;
ALTER ROLE mmuser NOBYPASSRLS NOREPLICATION NOCREATEDB NOCREATEROLE NOSUPERUSER;
```
Even though you can apply the changes in a non-downtime it's required to restart the containers.