Graph
Cases2 cases
1 to 2 of 2
- Symptoms
From 12:24 PM PST on 24 December 2012, the Amazon Elastic Load Balancing (ELB) control plane in the US-East Region showed high latency and error rates for API calls that manage load balancers. Running load balancers kept handling requests normally at first.
- Trigger
One of the very few developers with access to the production ELB environment inadvertently ran a maintenance process against the production ELB state data, and it logically deleted part of that data.
- Root cause
- Component
- Contributing factor
- Detection
The ELB team noticed the control plane API errors first; the missing state data was found only after the team investigated load balancers that had become degraded.
- Remediation
- Disabled several ELB control plane workflows, including scaling and descaling
- Recovered some of the affected running load balancers by hand
- Restored a snapshot of the ELB state data from just before the deletion, using an alternate recovery process
- Merged the restored data with the state changes since the snapshot and verified it
- Re-enabled the ELB workflows and APIs slowly while recovering each affected load balancer
- Action items
- Require per-incident Change Management approval for all access to production ELB state data
- Change the data recovery process so ELB state data can be recovered much faster
- Reprogram the ELB control plane workflows to reconcile central service data with current load balancer state
- Symptoms
From 12:47 AM PDT on 21 April 2011, a subset of Amazon EBS volumes in one Availability Zone of the US East Region could no longer serve reads or writes, and EC2 instances that tried to use them got stuck as well. AWS called these "stuck" volumes. EBS API calls across the whole US East Region also returned high error rates and latencies during two periods on the first day.
- Trigger
During a routine network change to upgrade the capacity of the primary EBS network in one Availability Zone, traffic was to be shifted off one of the redundant routers. The shift was executed incorrectly and sent the traffic onto the lower-capacity replication network instead of the other primary router, which could not carry it.
- Root cause
- Component
- Contributing factor
- Remediation
- Rolled back the incorrect traffic shift, which restored network connectivity
- Disabled all new Create Volume requests in the affected Availability Zone at 2:40 AM PDT
- Disabled all communication between the degraded EBS cluster and the EBS control plane from 8:20 AM PDT
- Stopped EBS servers in the degraded cluster from futilely contacting other servers for free space
- Changed the EBS control plane so new EBS-backed instance launches stopped failing
- Moved spare server capacity physically from across the US East Region into the degraded cluster
- Adjusted the negotiation throttles so the new servers could join without flooding the old ones
- Built a separate EBS control plane partitioned to the affected zone and finer-grained throttles, then processed the backlog
- Restored the remaining volumes from S3 snapshots taken early in the event
- Restored volumes on failed machines that had no snapshot after forensic work
- Intervened by hand on the RDS multi-AZ instances that did not fail over automatically
- Action items
- Audit the change process and add automation to prevent the traffic shift mistake
- Change capacity planning and alarming to keep the extra safety capacity needed for large recovery events
- Change the retry logic in EBS nodes to back off harder and reconnect to previous replicas instead of searching for new nodes
- Test and deploy the fix for the race condition that crashed EBS nodes
- Fix the RDS bug that kept multi-AZ instances from failing over automatically
- Improve the EBS control plane timeout logic to prevent thread exhaustion when one zone's cluster is slow
- Make the EBS control plane aware of Availability Zones so it sheds load when over capacity
- Move more EBS control plane functions into per-cluster services that run in the same zone as the cluster
- Offer multiple Availability Zones to Amazon VPC customers
- Provide better tools for building multi-AZ applications that survive the loss of a zone
- Host free webinars and publish whitepapers on fault-tolerant architecture
- Build the fine-grained control and throttling used in recovery into the EBS nodes and automate the recovery models
- Look at changes that keep volumes working while a cluster is degraded, including the ability to take a snapshot of a stuck volume
- Send more frequent and detailed customer updates and staff developer support more widely during events
- Develop tools that show through the APIs whether instances are impaired
- Lessons
AWS writes that with more spare capacity the cluster would have absorbed the re-mirroring requests without a storm, and that it now understands how much capacity large recovery events need. The event also showed that the EBS control plane let a failure in one Availability Zone affect the others, so more work is needed to make zones behave as if completely independent. AWS adds that some customers had critical components in a single zone, and that multi-AZ deployments need to become easier to design and run.
These 2 cases involve Cloud block storage and Cloud load balancer. 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.
By root cause1
Operator error2 cases
- Contributing factor
- Organisation