cloud-sql-psc-ports
Cloud SQL PSC port mapping — MySQL vs PostgreSQL, direct connection vs Auth Proxy. Captures that Auth Proxy for PostgreSQL uses port 3307, not 5432.
SKILL.mdskills/gcp/cloud-sql-psc-ports/SKILL.md
GitHubCloud SQL PSC Port Reference
Overview
Domain knowledge about Cloud SQL Private Service Connect (PSC) port mapping for MySQL and PostgreSQL. Captures the non-obvious insight that Cloud SQL Auth Proxy uses different ports than the database default.
MySQL PSC Ports
| Port | Purpose |
|---|---|
| 3306 | Direct connection / Managed Connection Pooling |
| 3307 | Cloud SQL Auth Proxy |
PostgreSQL PSC Ports
| Port | Purpose |
|---|---|
| 5432 | Direct connection |
| 6432 | PgBouncer (Managed Connection Pooling) |
| 3307 | Cloud SQL Auth Proxy (NOT 5432) |
Key Insight
Auth Proxy for PostgreSQL uses port 3307 for outbound connections, not PostgreSQL's default 5432.
Traffic path:
Pod → Auth Proxy (local:5432) → PSC Endpoint (:3307) → Cloud SQL (:5432)
If NetworkPolicy only allows 5432, Auth Proxy outbound connections will be blocked even though the local proxy listens on 5432.
Sources
- https://cloud.google.com/sql/docs/postgres/about-private-service-connect
- https://cloud.google.com/sql/docs/mysql/about-private-service-connect
Trigger
Use when:
- Designing PSC-based Cloud SQL connectivity from GKE
- Debugging NetworkPolicy issues with Cloud SQL connections
- Investigating why only opening the database port (e.g., 5432) doesn't work with Auth Proxy