Cases2 cases

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1. IL-0552 CircleCI's archival database ran out of storage, slowing workflow and job starts and the display of workflows in the UI

   CircleCI2025

   Symptoms

   At about 23:00 UTC on 21 January 2025, an automated alert reported that the CircleCI database instance holding archived data was almost out of free storage space. From 23:50 UTC customers saw slow starts and cancellations of workflows and jobs, and delays and difficulty viewing workflows in the CircleCI UI, although pipelines for a specific project could still be viewed.

   High latencyIntermittent timeoutsLog floodNode disk fullCloud API rate limit exhausted

   Trigger

   A code change to a function in the archival database on 16 January 2025 unintentionally made it write an excessive number of log messages, and the database filled its storage.

   Root cause

   Faulty deployment

   Component

   DatabaseCI system

   Contributing factor

   Change with a delayed effectExcessive blast radiusOverlapping failures

   Detection

   An automated alert at about 23:00 UTC warned that the archival database was almost out of free storage, before customers were affected. The growing workflows queue was not linked to it at first because a separate alert about request volume fired at about the same time.

   Remediation

   • Scaled up the event consumer that processes the workflows queue at 23:44 UTC
   • Promoted a read replica of the archival database to a standalone primary at 23:55 UTC

   Action items

   • Fix the database function so it no longer writes an excessive number of log messages
   • Add a max duration to the workflows retry policy for archiving so it fails earlier than the default timeout
   • Move workflow archival to an event-based model that decouples it from the workflows service
   • Add forecast and anomaly monitoring for databases that alerts on unusual activity before it reaches critical levels

   Lessons

   The storage alert on the archival database did fire, but the database filled much faster than forecast, so there was little time to act before customers were affected. Because the workflows service called the archival service synchronously, a problem in the archival database slowed the whole workflows service.

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2. IL-0328 A field type change in the database of CircleCI's job distribution service left all jobs stuck in "not running"

   CircleCI2021

   Symptoms

   From about 18:50 to 19:43 UTC on Monday, November 8, 2021, CircleCI customer jobs on all executors were blocked in a "not running" state. Errors and alerts appeared right after a deploy that changed a field type in the database of the job distribution service.

   Service outageHigh latencyScale-up failureCloud API rate limit exhausted

   Trigger

   At 18:50 UTC a deploy changed the type of a field in the PostgreSQL database of the job distribution service, in a way that was not backwards compatible.

   Root cause

   Faulty deployment

   Component

   DatabaseNode pool

   Contributing factor

   Ineffective rollbackExcessive blast radiusGap in automated tests

   Detection

   Errors and alerts related to the distribution failure appeared immediately after the 18:50 UTC deploy.

   Remediation

   • Rolled back the field type change, which did not clear the errors
   • Wrote, built and manually deployed a change that made the distribution system ignore the field
   • Manually scaled the primary compute cluster for the expected thundering herd of work
   • Monitored until processing was normal and resolved the incident

   Action items

   • Fix the gaps found in the testing strategy
   • Change how the distributor reacts to unexpected data so that this kind of deploy should not affect all jobs
   • Make recovery faster when unforeseen failures occur

   View case

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