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1. IL-0222 Google Cloud US regions had heavy packet loss and some went unreachable after the network control plane was descheduled

   Google Cloud2019

   Symptoms

   On Sunday 2 June 2019, with user impact beginning between 11:47 and 11:49 US/Pacific, Google Cloud projects in several US regions saw elevated packet loss from network congestion, and some regions became unreachable. Customers saw higher latency, intermittent errors and lost connectivity to instances in us-central1, us-east1, us-east4, us-west2, northamerica-northeast1 and southamerica-east1, while us-west1, Europe and Asia had no regional congestion.

   Packet lossNetwork unreachableHigh latencyHigh error rateMonitoring outage

   Trigger

   At 11:45 US/Pacific a relatively rare type of datacenter maintenance event started in one physical location, and the automation that runs it descheduled logical clusters that also held network control plane jobs in other physical locations.

   Root cause

   Software defect

   Component

   Network control plane (SDN)BGP routingBackbone network (WAN)

   Contributing factor

   Excessive blast radiusCircular dependencyLimited debug accessIneffective rollback

   Detection

   Google engineers were alerted to the failure two minutes after it began and started the incident process used for the most serious production incidents. The first customer notice appeared on the status page at 12:53 US/Pacific.

   Remediation

   • Lowered the priority of less critical network traffic classes to reduce congestion
   • Halted the datacenter automation software responsible for the maintenance event
   • Rescheduled the network control plane and its supporting infrastructure in each location
   • Rebuilt and redistributed the lost network control plane configuration, rolling it out from 14:03
   • Directed service traffic away from the affected regions
   • Moved the Cloud VPN control plane in three regions out of its fail-safe state

   Action items

   • Keep the maintenance automation off until safeguards stop it descheduling jobs in several physical locations at once
   • Harden the cluster management software to reject such requests whatever their origin
   • Reconfigure the network control plane to reject maintenance requests of the type involved
   • Make the network control plane in each location persist its configuration
   • Let the network stay in fail static mode longer when the control plane is lost
   • Review, update and test emergency response tooling and procedures, including customer communication tooling, for such network failures
   • Extend continuous disaster recovery testing to this and similarly catastrophic failures

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