IAM login is not the whole database permission model
Cloud SQL for PostgreSQL can authenticate database users through IAM instead of a stored database password. The connection still crosses separate boundaries: reaching the instance through the connector, having IAM login permission, mapping to the intended database account, and possessing SQL privileges inside the database.
IAM access tokens are short-lived. Copying one token into a long-lived password setting can let initial connections succeed and later replacement connections fail. Automatic IAM database authentication delegates supported token acquisition and refresh to a Cloud SQL connector. The connector's identity must match the IAM account used to authenticate to the database. A connection pool does not remove this requirement when it creates new connections.
Prepare a staging instance, the deployed runtime identity, current database flags and user configuration, connector version, and application pool settings. Obtain read-only configuration access and an approved database test user. Do not log access tokens or place them in a connection string committed to source control.
Establish the supported identity path
- Inspect
gcloud sql instances describe INSTANCE --project=PROJECT_ID. Confirm the PostgreSQL instance and IAM database-authentication configuration. Readgcloud sql users list --instance=INSTANCE --project=PROJECT_IDto inspect the configured account types without exposing credentials. - Identify the credentials the connector actually uses. A development shell, application runtime, and sidecar proxy can each resolve Application Default Credentials differently. Check the required connection and IAM database-login permissions for that principal at the intended scope.
- Configure automatic IAM authentication using a supported connector and the documented database username format. Match the database login account to the connector's IAM identity. Grant only the SQL schema and table privileges required by the application; successful IAM authentication does not authorize every SQL operation.
- Test pool replacement behavior. Open a fresh connection after the application has been running for a realistic period, and exercise the connector's supported refresh path. Review client-side connection lifetime and retry settings so stale connections are replaced without a connection storm.
Illustrative scenario
A fictional reporting API uses a manually generated token as a startup password. It works initially, but new pool connections fail later while some old sessions still serve requests. The team moves token handling to the supported automatic connector flow and verifies that the connector runs as the intended service account. It separately grants read access to the reporting schema. The change addresses authentication lifecycle without granting database administration rights.
| Observation | Boundary to inspect | Corrective direction |
|---|---|---|
| Connector cannot reach the instance | Connection IAM and network path | Repair the supported connector access |
| New connections fail later | Manual token and refresh behavior | Use automatic token management |
| Login succeeds, query is denied | PostgreSQL SQL grants | Grant the required database privileges |
| Wrong user appears in sessions | Connector ADC and username mapping | Align the runtime identity |
Verify with safe database operations
Confirm the authenticated database identity using an approved session query and read a permitted test table. Verify an out-of-scope operation remains denied. Restart or recycle staging pool connections and repeat the login after token refresh should have occurred. Watch both connector diagnostics and PostgreSQL errors to separate connection, authentication, and SQL authorization failures.
Operating procedure
Document instance, connector mode, runtime identity, database account, and SQL privilege owner. Monitor new-connection failures and pool exhaustion separately. Revalidate when changing service accounts, connector versions, deployment platforms, or database grants. Keep emergency access separate from ordinary application login so a troubleshooting account does not silently replace the intended IAM path.
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