Agent-Skills.md

Agent Skills: Cloud SQL PSC Port Reference

Cloud SQL PSC port mapping — MySQL vs PostgreSQL, direct connection vs Auth Proxy. Captures that Auth Proxy for PostgreSQL uses port 3307, not 5432.

UncategorizedID: aibangjuxin/knowledge/cloud-sql-psc-ports

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aibangjuxin/knowledge
aibangjuxin
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pnpm dlx add-skill https://github.com/aibangjuxin/knowledge/tree/HEAD/skills/gcp/cloud-sql-psc-ports

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skills/gcp/cloud-sql-psc-ports/SKILL.md

Skill Metadata

Name
cloud-sql-psc-ports
Description
Cloud SQL PSC port mapping — MySQL vs PostgreSQL, direct connection vs Auth Proxy. Captures that Auth Proxy for PostgreSQL uses port 3307, not 5432.

Cloud 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