docs(postgres): add migration guide and update to postgres 15.17

docs/04-operations/01-site-operations.md

@@ -15,17 +15,12 @@ docker-compose exec backend bench new-site --mariadb-user-host-login-scope=% --d
 
 If you need to install some app, specify `--install-app`. To see all options, just run `bench new-site --help`.
 
-To create Postgres site (assuming you already use [Postgres compose override](../02-setup/05-overrides.md)) you need have to do set `root_login` and `root_password` in common config before that:
+To create a Postgres site (assuming you already use [Postgres compose override](../02-setup/05-overrides.md)), the `root_login` and `root_password` are now automatically set by the `configurator`. For major version upgrades, please refer to the [Postgres Migration Guide](../06-migration/03-postgres-major-version-upgrade.md).
+
+To create a new Postgres site:
 
 ```sh
-docker-compose exec backend bench set-config -g root_login <root-login>
+docker-compose exec backend bench new-site --db-type postgres --admin-password <admin-password> <site-name>
-docker-compose exec backend bench set-config -g root_password <root-password>
-```
-
-Also command is slightly different:
-
-```sh
-docker-compose exec backend bench new-site --mariadb-user-host-login-scope=% --db-type postgres --admin-password <admin-password> <site-name>
 ```
 
 ## Push backup to S3 storage

docs/06-migration/03-postgres-major-version-upgrade.md

@@ -0,0 +1,40 @@
+# PostgreSQL Major Version Upgrade (v13 to v15)
+
+Upgrading PostgreSQL from version 13 to 15 is a major version jump. Since PostgreSQL does not support in-place data directory upgrades, existing users must manually migrate their data using `pg_dump`.
+
+### **Migration Steps**
+
+1. **Backup Existing Data (Version 13):**
+   Before updating your compose file, ensure your containers are running and perform a dump of all databases.
+   ```bash
+   docker exec -it <project_name>-db-1 pg_dumpall -U postgres > full_dump.sql
+   ```
+
+2. **Stop and Remove Containers:**
+   ```bash
+   docker compose down
+   ```
+
+3. **Delete Old Data Volume:**
+   PostgreSQL 15 cannot read data created by version 13. You must remove the existing volume (Warning: this deletes the old data directory).
+   ```bash
+   docker volume rm <project_name>_db-data
+   ```
+
+4. **Update Image and Start (Version 15):**
+   Update your `overrides/compose.postgres.yaml` (or pull the latest changes) and start the containers.
+   ```bash
+   docker compose up -d
+   ```
+
+5. **Restore Data:**
+   Restore the dump into the new PostgreSQL 15 instance.
+   ```bash
+   cat full_dump.sql | docker exec -i <project_name>-db-1 psql -U postgres
+   ```
+
+6. **Verify and Clean Up:**
+   Ensure your sites are working correctly with `bench migrate` and then remove the `full_dump.sql` file.
+   ```bash
+   docker exec -it <project_name>-backend-1 bench --site all migrate
+   ```

overrides/compose.postgres.yaml

@@ -8,7 +8,7 @@ services:
         condition: service_healthy
 
   db:
-    image: postgres:15-alpine
+    image: postgres:15.17
     command: []
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U postgres"]