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  1. IL-0388 A Google Cloud live migration took a Discord Redis primary offline, and the failover broke API instances and then guilds
    Discord2017
    Symptoms

    At about 14:01 PDT on 13 October 2017, Discord engineers were alerted to anomalies by real-time metrics and monitoring. A Redis instance that was the primary of a highly available cluster used by the API services had dropped offline after Google Cloud Platform migrated it automatically, and some API instances did not handle the failover to the secondary node correctly.

    Failover failureHigh latencyService outage
    Trigger

    Google Cloud Platform automatically migrated the Redis instance that was the primary of a highly available cluster used by the API services, and the node incorrectly dropped offline.

    Root cause
    Software defect
    Component
    In-memory cacheDatabaseCDN and edge network
    Contributing factor
    Unpatched known bugOverlapping failuresMonitoring blind spot
    Detection

    Real-time metrics and monitoring alerted engineers at 14:01 PDT. The second phase was seen at 15:41 as another anomaly in monitoring, and end user reports of servers appearing offline were escalated at 15:42.

    Remediation
    • Ran a rolling restart of all API instances to clear the Redis connection issues
    • Corrected the misconfigured edge caching rule for the expensive API route
    • Disabled the problem API endpoint on the edge network
    • Recovered the Cassandra cluster
    • Ran a second rolling restart of all API instances for the latency left by the Cassandra issues
    • Removed the misbehaving guilds node from the service hashring
    • Forcefully restarted the misbehaving guilds node
    • Restarted the whole service, forcing all users to reconnect
    • Blocked traffic that relied on the failing push component to reduce its load
    • Corrected the API setting that lets users reconnect quickly and safely
    Action items
    • Fix the known issues with Redis failover within the coming weeks
    • Change the cached route so this type of error does not degrade other services
    • Monitor the signals that would have warned of the cascading failure
    • Improve the reliability and failure handling of the affected services
    • Roll out an update of the library with the suspected flaws
    View case
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This case involves In-memory cache and CDN and edge network. kubegap audits a Kubernetes cluster for gaps like these, read-only, from Claude Code or Codex; its checks cite public reports like the ones in this library.

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By root cause1

Software defect1 case

Component
In-memory cacheCDN and edge networkDatabase
Contributing factor
Unpatched known bugMonitoring blind spotOverlapping failures
Organisation
Discord
  1. IL-0388 A Google Cloud live migration took a Discord Redis primary offline, and the failover broke API instances and then guilds
    Discord2017