chore(deps): update postgres docker tag from 17.6 to v18 (docker-compose.yml) (#13262)

* chore(deps): update postgres docker tag from 17.6 to v18 (docker-compose.yml)

* Add upgrade notes

---------

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: Cody Maffucci <46459665+Maffooch@users.noreply.github.com>

Author: renovate[bot]

docker-compose.yml

@@ -120,7 +120,7 @@ services:
           source: ./docker/extra_settings
           target: /app/docker/extra_settings
   postgres:
-    image: postgres:17.6-alpine@sha256:855021a5b10954343902a8c22a15f8464233126c1d12d9ad84d4a14c5af07a80
+    image: postgres:18.0-alpine@sha256:aa7c4a8932f5bafe14700a789339d102251d0f7d53503a201247b5f5990da5e2
     environment:
       POSTGRES_DB: ${DD_DATABASE_NAME:-defectdojo}
       POSTGRES_USER: ${DD_DATABASE_USER:-defectdojo}

docs/content/en/open_source/upgrading/2.51.md

@@ -1,8 +1,8 @@
 ---
-title: 'Upgrading to DefectDojo Version 2.51.x'
+title: "Upgrading to DefectDojo Version 2.51.x"
 toc_hide: true
 weight: -20250902
-description: Helm chart changes.
+description: Helm chart changes and Postgres major version updates.
 ---
 
 ## Helm Chart Changes
@@ -44,6 +44,96 @@ The following Helm chart values have been modified in this release:
 - **Fixed secret mounting**: Resolved issues with optional secret mounts and references.
 - **Improved code organization**: Minor Helm chart refactoring to enhance readability and maintainability.
 
+## PostgreSQL Major Version Upgrade in Docker Compose
+
+This release incorporates a major upgrade of Postgres. When using the default docker compose setup you'll need to upgrade the Postgres data folder before you can use Defect Dojo 2.51.0.
+
+There are lots of online guides to be found such as https://hub.docker.com/r/tianon/postgres-upgrade or https://github.com/pgautoupgrade/docker-pgautoupgrade.
+
+There's also the [official documentation on `pg_upgrade`](https://www.postgresql.org/docs/current/pgupgrade.html), but this doesn't work out of the box when using Docker containers.
+
+Sometimes it's easier to just perform the upgrade manually, which would look something like the steps below.
+It may need some tuning to your specific needs and docker compose setup. The guide is loosely based on https://simplebackups.com/blog/docker-postgres-backup-restore-guide-with-examples.
+If you already have a valid backup of the postgres 16 database, you can start at step 4.
+
+### 0. Backup
+
+Always back up your data before starting and save it somewhere.
+Make sure the backup and restore is tested before continuing the steps below where the docker volume containing the database will be removed.
+
+### 1. Start the Old Postgres Container
+
+If you've acceidentally already updated your docker-compose.yml to the new versions, downgrade to postgres 16 for now:
+
+Edit your `docker-compose.yml` to use the old Postgres version (e.g., `postgres:17.6-alpine`):
+
+```yaml
+postgres:
+  image: postgres:17.6-alpine
+  ...
+```
+
+Start only the Postgres container which will now be 17.6:
+
+```bash
+docker compose up -d postgres
+```
+
+### 2. Dump Your Database
+
+```bash
+docker compose exec -t postgres pg_dump -U defectdojo -Fc defectdojo -f /tmp/defectdojo.dump
+docker cp <postgres_container_name>:/tmp/defectdojo.dump defectdojo.dump
+```
+
+You can find the postgres_container_name via `docker container ls` or `docker ps`.
+
+### 3. Stop Containers and Remove the Old Volume
+
+You can find the volume name via `docker volume ls`.
+
+```bash
+docker compose down
+docker volume rm <defectdojo_postgres_volume_name>
+```
+
+### 4. Switch to the New Postgres Version
+
+Edit your `docker-compose.yml` to use the new version (e.g., `postgres:18-alpine`):
+
+```yaml
+postgres:
+  image: postgres:18-alpine
+  ...
+```
+
+### 5. Start the New Postgres Container
+
+```bash
+docker compose up -d postgres
+```
+
+### 6. Restore Your Database
+
+**Copy the dump file into the new container:**
+
+```bash
+docker cp defectdojo.dump <postgres_container_name>:/defectdojo.dump
+```
+
+**Restore inside the container:**
+
+```bash
+docker exec -it <postgres_container_name> bash
+pg_restore -U defectdojo -d defectdojo /defectdojo.dump
+```
+
+### 7. Start the Rest of Your Services
+
+```bash
+docker compose up -d
+```
+
 ---
 
 There are other instructions for upgrading to 2.51.x. Check the [Release Notes](https://github.com/DefectDojo/django-DefectDojo/releases/tag/2.51.0) for the contents of the release.