High availability still interrupts sessions
Cloud SQL high availability can move database service to a standby during a failover. Applications continue using the instance's connection address, but existing connections are closed. The database's recovery and the application's recovery are therefore different events. A service can remain unhealthy after the database returns if its pool keeps handing out broken sessions or overwhelms the instance while reconnecting.
Maintenance also has application consequences for HA instances. Do not translate a regional HA configuration into a promise of uninterrupted transactions. An operation interrupted near commit can require business reconciliation because a client error does not always prove that no effect occurred. The recovery design must distinguish safe retries from uncertain write outcomes.
Prepare an approved staging HA instance, production-like pool configuration, representative safe transactions, and a controlled failover window. Identify application and database owners. Record the instance configuration, maintenance settings, dependency timeouts, and the user-facing recovery objective. A production failover is a change requiring the normal operational process, not a casual diagnostic command.
Build the drill around the application
- Inspect
gcloud sql instances describe INSTANCE --project=PROJECT_ID. Confirm the HA configuration, connection method, and maintenance policy. Read recent instance operations to establish the current state before scheduling a drill. - Review pool behavior when connections fail. Check whether broken sessions are discarded, new connections use bounded exponential backoff with jitter, and request deadlines prevent indefinite waiting. Calculate total potential connections across application replicas so recovery does not exceed the database's capacity.
- Run the approved failover in the isolated or scheduled environment while sending harmless representative reads and writes. Record when errors begin, when fresh connections succeed, and when the business workflow becomes useful again. Keep the same intended instance address rather than rewriting clients toward a transient backend.
- Reconcile interrupted write operations using stable business identifiers. Confirm retries do not create duplicate records or repeat external effects. Fix application recovery problems, then repeat only the focused part of the drill needed to verify those changes.
Illustrative scenario
A fictional order service survives the database failover at the infrastructure level, but every application replica immediately opens its maximum pool size. The connection surge slows recovery and fills the request queue. The team reduces eager pool creation, adds bounded jittered reconnects, and limits waiting requests. The next approved drill demonstrates recovery of a sample order workflow as well as database availability.
| Evidence | Likely application issue | Correction |
|---|---|---|
| Database is ready, app keeps failing | Broken sessions retained | Discard and replace failed connections |
| Reconnect traffic spikes together | Synchronized retries or eager pools | Bound and spread reconnection |
| Requests wait after recovery | Queue and deadline behavior | Enforce useful request timeouts |
| Duplicate writes appear | Uncertain transaction outcome | Reconcile by business operation identity |
Verify a usable recovery
Confirm fresh reads and writes through the real application connection path. Check database connection count, application pool health, latency, and queued work. Verify representative records created around the interruption. Measure the recovery interval from the agreed user-impact event, including application stabilization. Document the observed result rather than treating a documentation estimate as your application's guaranteed recovery time.
Operating procedure
Rehearse after major driver, connector, pool, or transaction changes. Monitor connection failures, connection creation rate, request backlog, and incomplete business operations. Keep maintenance notifications and the application's on-call procedure aligned. Store the last drill's acceptance evidence with the recovery plan so HA remains an exercised capability rather than a configuration label.
Explore Clouvenix backup disaster recovery for implementation and operational handover.