# db_primary_down: primary unreachable (layer 3)

Symptoms: probe_success{target="db-primary"} = 0, api 5xx on /api/orders and /api/price, legacy-api logs show connection refused or timeout to 10.20.0.20:5432.

Decision tree for the human: 1) Is the VM RUNNING and only PostgreSQL down? Restart PostgreSQL on the primary (service restart; layer 1 systemd handles crashes). 2) Is the VM stopped or lost? gce.instance_reset or recreate through Terraform. 3) Only if the primary cannot come back: promote the replica (`SELECT pg_promote()` on selfheal-db-replica) and switch the application DSN to 10.20.0.21; this is irreversible (timeline fork), the old primary must be re-cloned. The agent must escalate, never propose promotion.