chore: Upgrade local & dev postgres to 18

[martyngigg]

Summary

Matches version deployed in external database service after upgrade.

Change in mount path due to error message on first boot with original mount path:

Error: in 18+, these Docker images are configured to store database data in a
format which is compatible with "pg_ctlcluster" (specifically, using
major-version-specific directory names). This better reflects how
PostgreSQL itself works, and how upgrades are to be performed.

   See also https://github.com/docker-library/postgres/pull/1259

   Counter to that, there appears to be PostgreSQL data in:
     /var/lib/postgresql/data (unused mount/volume)

   This is usually the result of upgrading the Docker image without
   upgrading the underlying database using "pg_upgrade" (which requires both
   versions).

   The suggested container configuration for 18+ is to place a single mount
   at /var/lib/postgresql which will then place PostgreSQL data in a
   subdirectory, allowing usage of "pg_upgrade --link" without mount point
   boundary issues.

   See https://github.com/docker-library/postgres/issues/37 for a (long)
   discussion around this process, and suggestions for how to do so.

Summary by CodeRabbit

• Chores
  • PostgreSQL database upgraded from version 16.9 to version 18 across all environments, bringing performance and security enhancements.
  • Database storage configuration optimised for improved resource utilisation.

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📝 Walkthrough

Walkthrough

This pull request updates PostgreSQL from version 16.9 to 18 across infrastructure configurations. The Ansible role's default image variable is updated, and the Docker Compose configuration adjusts both the PostgreSQL image reference and modifies the database volume mount path.

Changes

Cohort / File(s)	Summary
PostgreSQL Version Upgrade infra/ansible/roles/postgres/defaults/main.yml, infra/local/docker-compose.yml	PostgreSQL image bumped from 16.9-bookworm to 18-bookworm across both Ansible and Docker Compose configurations. Docker Compose volume mount path changed from /var/lib/postgresql/data to /var/lib/postgresql.

Poem

🐰 A rabbit's cheer for databases grand,
From version sixteen to eighteen's land!
New postgres paths we've arranged with care,
Volume mounts shifted here and there!
Infrastructure hops to fresh frontiers fair! 🚀

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The pull request title accurately describes the main change: upgrading PostgreSQL from version 16.9 to version 18 across local and development environments, which is confirmed by updates to both the Ansible configuration and Docker Compose file.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@infra/local/docker-compose.yml`:
- Line 108: Docker Compose mounts Postgres data to /var/lib/postgresql which
mismatches the Ansible role expecting /var/lib/postgresql/data; update the
docker-compose service volume entry (the string
"shared_database_data:/var/lib/postgresql") to
"shared_database_data:/var/lib/postgresql/data" so both environments use the
same data directory and avoid initialization discrepancies.

---

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📥 Commits

Reviewing files that changed from the base of the PR and between 0700e4c and d15c8c8.

📒 Files selected for processing (2)

• infra/ansible/roles/postgres/defaults/main.yml
• infra/local/docker-compose.yml