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Cases6 cases

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  1. IL-0303 GitHub's MySQL master failed over to a node with a cold buffer pool during a schema migration and GitHub.com went down
    GitHub2012
    Symptoms

    On Monday, September 10th, 2012, during a schema migration, the health checks on GitHub's MySQL master failed and Percona Replication Manager moved the 'active' role to another node of the new three-node cluster. That node's InnoDB buffer pool was cold and it performed poorly, its health checks failed in turn, and the role failed back to the original server. GitHub.com went down.

    Failover failureDatabase overloadHigh latencyReplication lagSplit brainService outage
    Trigger

    A schema migration on Monday, September 10th put more load on the master database than earlier migrations had, and Percona Replication Manager's health checks on the master failed.

    Root cause
    Software defect
    Component
    DatabaseDatabase failover managerDatabase replication
    Contributing factor
    Automation amplificationDependence on a warm cacheHarmful manual actionOverlapping failures
    Detection

    On the morning of September 11th, a developer told the operations team that the 'standby' node was returning incorrect query results.

    Remediation
    • Enabled Pacemaker's maintenance-mode so no health checks or automatic failovers ran, and let the buffer pool warm
    • Powered off the out-of-date node 'c' to end the partition
    • Stopped Pacemaker and Heartbeat on nodes 'a' and 'b' and started them on node 'a' only
    • Started MySQL on node 'a' in the active role
    • Removed the events leaked to wrong dashboards and audited the wrongly routed repositories
    • Contacted the owners of the exposed private repositories
    Action items
    • Change the Pacemaker configuration so the active database role fails over only when an operations engineer starts it
    • Find a way to warm the InnoDB buffer pool of slave databases so failovers do not hurt performance
    • Audit the Pacemaker and Heartbeat stack, focusing on the code path behind the segfault
    • Run hardware tests on the server where the segfault happened
    Lessons

    GitHub concluded that automated failover is not the right strategy for its primary production database: for every failover in this incident, any member of the operations team would have said it should not happen. Failovers that must happen, in an emergency or during maintenance, should not hurt performance.

    View case
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These 6 cases involve Database failover manager and Database. 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 cause5

Software defect2 cases

Component
Database2Database failover manager2Database replication1
Contributing factor
Harmful manual action2Overlapping failures2Unverified assumption1Automation amplification1Excessive blast radius1Change with a delayed effect1Monitoring blind spot1Dependence on a warm cache1
Organisation
GitHub1Stripe1
  1. IL-0241 A database shard could not elect a new primary, and the Stripe API failed most requests in two periods on one day
    Stripe2019
  2. IL-0303 GitHub's MySQL master failed over to a node with a cold buffer pool during a schema migration and GitHub.com went down
    GitHub2012

Configuration change1 case

Component
In-memory cacheDatabase replicationDatabase failover manager
Contributing factor
Automation amplificationOverlapping failures
Organisation
Hatena
  1. IL-0430 Mackerel's Redis stopped answering during a replication setup, keepalived failed over by mistake, and Mackerel degraded
    Hatena2018

Hardware failure1 case

Component
DatabaseDatabase failover manager
Contributing factor
Unverified assumptionOverlapping failures
Organisation
GoCardless
  1. IL-0219 GoCardless's API and Dashboard failed every request for 1 hour 50 minutes when Pacemaker did not promote a replica
    GoCardless2017

Operator error1 case

Component
DatabaseDatabase replicationDatabase failover manager
Contributing factor
Automation amplificationUnreviewed defaultsOverlapping failuresUnrepresentative staging
Organisation
Hatena
  1. IL-0431 During Mackerel's move to AWS, PostgreSQL failed over to a replica that had stopped replicating, losing an hour of data
    Hatena2017

Faulty deployment1 case

Component
In-memory cacheAuthoritative DNS servers and recordsDatabase failover manager
Contributing factor
Overlapping failures
Organisation
Redis
  1. IL-0278 A weekly update put a Redis Cloud management process into an infinite loop, and most nodes of a GCP cluster failed
    Redis2016