Cases2 cases

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1. IL-0318 Clerk's APIs went down with lock contention and 429s while a Google Cloud SQL live migration slowed its database disk

   Clerk2026

   Symptoms

   At 15:57 UTC on 10 March 2026, Clerk's alerting reported increased latency and elevated 5xx errors across its APIs, and the incident was declared. Monitoring showed increased lock contention in the database, which had started about a minute earlier.

   High latencyHigh error rateLock contention or deadlockService outage

   Trigger

   A routine live migration of the Google Cloud SQL virtual machine that hosts Clerk's Postgres database, done without advance notice to Clerk, did not work as intended.

   Root cause

   Cloud provider outage

   Component

   Database

   Contributing factor

   Limited debug access

   Detection

   Alerting reported increased latency and elevated 5xx errors across the APIs at 15:57 UTC, and monitoring showed lock contention in the database that had begun about a minute earlier.

   Remediation

   • Enabled Origin Outage Mode to keep session management working
   • Opened a ticket with GCP after seeing elevated IO wait on reads
   • Disabled Origin Outage Mode after the live migration completed and the system stabilised

   Action items

   • Ask Google to pin the database again to stop further live migrations
   • Use replica promotion instead of live migrations for all Postgres database maintenance
   • Move to another database provider or run Postgres in-house unless Google offers a way to disable live migrations permanently
   • Return 500 instead of the internal service's 429 so applications can tell the state of Clerk's systems from the error code
   • Shift most of the engineering team to reliability-focused projects

   Lessons

   Clerk concludes that Cloud SQL live migrations are still unsafe after months of joint work with Google, and that they are opaque, leaving Clerk to trust Google's word. Clerk prefers traditional replica promotion for all Postgres maintenance, an automated process it had already used without incident for a Postgres major version upgrade on January 17, 2026.

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2. IL-0315 Railway's backend API went down when an index build locked a billion-row Postgres table and used up every connection

   Railway2025

   Symptoms

   At 18:36 UTC on 28 October 2025, two minutes after a database change went live in production, Railway's internal monitoring alerted and paged the engineering team. The dashboard could not be opened, CLI operations that use the API, such as railway up, failed, GitHub-based deployments were delayed because webhook processing failed, and all Railway Public API operations were disrupted.

   Service outageLock contention or deadlockDatabase overload

   Trigger

   A routine schema change to the backend's Postgres database, introduced at 18:23 UTC and live in production at 18:34 UTC, that added a new column with an index without the CONCURRENTLY option.

   Root cause

   Faulty deployment

   Component

   DatabaseDatabase proxy and connection pooler

   Contributing factor

   No configuration testsLimited debug access

   Detection

   Internal monitoring alerts paged the engineering team at 18:36 UTC, and the incident was declared at 18:41 UTC.

   Remediation

   • The index migration finished after about 30 minutes and released the table lock, and the queued operations and connection pools recovered

   Action items

   • Enforce CONCURRENTLY for all index creation in CI and block pull requests that do not use it
   • Adjust PgBouncer pool limits so they cannot overwhelm the Postgres instance's capacity
   • Configure database user connection limits so administrative access stays possible during incidents

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