Incident Library
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Cases3 cases

1 to 3 of 3

  1. IL-0367 Azure Storage in Central US rejected VM disk I/O, taking down VMs and the SQL Database and Cosmos DB services on them
    Microsoft Azure2024
    Symptoms

    From 21:40 UTC on 18 July 2024, virtual machines in the Azure Central US region lost access to their disks, and the services running on those VMs failed. Azure SQL Database and SQL Managed Instance showed unhealthy nodes and login failures, Cosmos DB requests failed, and service management operations failed across many Azure services.

    Storage disconnected or stale mountsService outageHigh error rateFailover failureStale endpoint routing
    Trigger

    Routine changes to the VM host fleet led to a new allow list of VM host address ranges being generated and published to all Storage scale units in Central US. Recent network configuration changes had made some of the infrastructure file servers that hold the source data unreachable from the server generating the list, so the published list was incomplete.

    Root cause
    Configuration change
    Component
    Cloud block storageDatabaseDatabase failover manager
    Contributing factor
    Unsafe failure behaviourNo staged rolloutExcessive blast radiusMonitoring blind spot
    Detection

    Service monitoring detected the drop in VM availability at 22:06 UTC while the allow list update was being published. SQL monitoring detected unhealthy nodes and login failures within one minute of SQL becoming unavailable, and monitoring flagged the availability drop for Cosmos DB, SQL DB and SQL DB Managed Instance at 22:14 UTC.

    Remediation
    • Halted the allow list update workflow worldwide
    • Paused all deployments in the Central US region
    • Paused compute buildout deployments in all regions
    • Updated the configuration of all Storage scale units in Central US, restoring storage availability by 02:55 UTC
    • Started geo-failovers for SQL databases with automatic failover policies
    • Restarted SQL gateway nodes to refresh their caches and route connections to the right nodes
    • Forced completion of SQL failovers that had not completed
    • Failed over the Cosmos DB control plane and active-passive accounts with a write region in Central US
    • Cancelled customer-triggered graceful switch region operations that blocked Cosmos DB failovers
    • Removed locks on Cosmos DB service metadata to force-complete stuck failovers
    • Repaired impacted Cosmos DB partitions for single-region accounts
    • Repaired backend nodes and failed Cosmos DB accounts back to Central US, redoing failback where it failed
    Action items
    • Make the allow list generation workflow detect incomplete source information and halt
    • Alert on storage requests rejected by allow list checks
    • Deploy allow lists one Availability Zone and storage type at a time, over 24 hours
    • Add VM health checks and an automatic stop to the allow list deployment workflow
    • Reevaluate the policy for Microsoft-managed failover of SQL failover groups
    • Fix the Cosmos DB failback workflow that broke some MongoDB drivers for MongoDB API accounts
    • Fix Cosmos DB failback for accounts with private endpoints so it does not need redoing
    • Make the storage data-plane firewall reject invalid allow lists and keep the last-known-good state
    • Improve Azure NetApp Files monitors so impacting events are detected and classified in time
    • Monitor more Azure NetApp Files service metrics to correlate similar events faster
    • Make the SQL Service Fabric cluster location change notifications reliable under load
    • Make SQL geo-failover workflows more robust so they complete
    • Remove the issues that delayed 5% of Cosmos DB failovers
    • Migrate Azure DevOps customer metadata to the right geography
    • Decouple Azure NetApp Files regional reads and writes to keep this class of issue to one region
    • Evaluate caching to reduce Azure NetApp Files reliance on stored utilization data
    • Add automatic per-partition failover for Cosmos DB multi-region active-passive accounts
    • Build the Resilient Ephemeral OS disk improvement so VMs survive storage incidents better
    View case
  2. IL-0291 GitLab.com's redis-sidekiq Sentinel could not elect a primary after a GCP host error, so Sidekiq was down for 30 minutes
    GitLab2023
    Symptoms

    GitLab.com showed widespread, erratic behaviour and more 500 errors for about 30 minutes while its redis-sidekiq Redis was down. Alerts in the #production channel began with Redis client errors and spread to error SLO violations on several services, such as the Webservice and API load balancer and Puma.

    Failover failureHigh error rate
    Trigger

    The VM of the primary node, redis-sidekiq-03-db-gprd, failed on a GCP host error and was reset and moved to another node.

    Root cause
    Cloud provider outage
    Component
    In-memory cacheDatabase failover manager
    Contributing factor
    Single point of failureMonitoring blind spot
    Detection

    Several alerts in the #production channel, first Redis client errors and then error SLO violations on several services, such as the Webservice and API load balancer and Puma.

    Remediation
    • Restarted the failed Redis node so Sentinel had enough nodes to elect a primary
    Action items
    • Alert when the Sentinel service is down
    • Make merge requests robust to Redis Sidekiq outages
    Lessons

    An alert on a down Sentinel node would have kept enough nodes up to form a quorum when failover was needed, and could have avoided the incident entirely. Removing a noisy alert earlier may have let the down node go unnoticed.

    View case
  3. 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
    Symptoms

    On 10 July 2019 the Stripe API failed a substantial majority of requests twice, from 16:35 to 17:02 UTC and from 21:14 to 22:47 UTC. In the first period automated monitoring detected within a minute that a database cluster had failed to elect a new primary.

    High error rateFailover failureWrites rejectedIntermittent timeoutsSustained high node CPU
    Trigger

    The primary node of a database cluster failed at 16:35 UTC while one shard had several stalled nodes. The second period was set off by rolling the election protocol back to the previous minor version at 20:42 UTC.

    Root cause
    Software defect
    Component
    DatabaseDatabase failover manager
    Contributing factor
    Change with a delayed effectMonitoring blind spotExcessive blast radiusHarmful manual actionUnverified assumptionOverlapping failures
    Detection

    Automated monitoring detected the failed election within a minute, and the team was alerted at 16:36 UTC. The second period was announced at 21:14 UTC by automated alerts that some shards in the cluster were unavailable.

    Remediation
    • Restarted all nodes of the database cluster, which forced a successful primary election
    • Updated the production configuration and restarted the database cluster's nodes
    • Ramped traffic back up, putting services for user-initiated API requests first
    Action items
    • Alert when nodes stop reporting their replication lag
    • Alert when a shard enters a state that could trigger the election fault
    • Work with the database maintainers on a fix for the underlying fault
    • Add circuit breaking on failed operations to particular database clusters
    • Use fault isolation to contain the impact of a single failed shard
    • Limit the resources used by clients that keep retrying failed requests
    • Add procedures and tooling that make rapid configuration changes during incident response safer
    View case
Check your cluster for this

These 3 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 cause3

Configuration change1 case

Component
Cloud block storageDatabaseDatabase failover manager
Contributing factor
Excessive blast radiusMonitoring blind spotNo staged rolloutUnsafe failure behaviour
Organisation
Microsoft Azure
  1. IL-0367 Azure Storage in Central US rejected VM disk I/O, taking down VMs and the SQL Database and Cosmos DB services on them
    Microsoft Azure2024

Cloud provider outage1 case

Component
In-memory cacheDatabase failover manager
Contributing factor
Monitoring blind spotSingle point of failure
Organisation
GitLab
  1. IL-0291 GitLab.com's redis-sidekiq Sentinel could not elect a primary after a GCP host error, so Sidekiq was down for 30 minutes
    GitLab2023

Software defect1 case

Component
DatabaseDatabase failover manager
Contributing factor
Unverified assumptionExcessive blast radiusChange with a delayed effectHarmful manual actionMonitoring blind spotOverlapping failures
Organisation
Stripe
  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