Cases3 cases

1 to 3 of 3

1. IL-0438 Builder Work became almost entirely unreachable with 504 errors when the Amazon CloudFront VPC Origins feature failed

   ANDPAD2026

   Symptoms

   At about 17:00 JST on Thursday 16 July 2026, Datadog alerted, and at almost the same time 5xx errors began to rise on the Amazon CloudFront distributions that used VPC Origins connections. Builder Work, ANDPAD's job and career service for the construction industry, became almost entirely unreachable.

   Service outageHigh error rate

   Trigger

   The Amazon CloudFront VPC Origins feature failed; AWS Health later reported a capacity constraint in an internal shared subsystem that manages connections for VPC Origins.

   Root cause

   Cloud provider outage

   Component

   CDN and edge networkCloud load balancerIngress controllerWeb application firewall rules

   Contributing factor

   Single point of failure

   Detection

   Datadog raised an alert, and at about the same time 5xx errors were seen rising on the CloudFront distributions that used VPC Origins.

   Remediation

   • Decided to route traffic temporarily through an internet-facing ALB without CloudFront
   • Recreated the internet-facing Ingress, attached it to the Argo Rollouts Rollout resource and promoted it
   • Created a regional WAF for the ALB with the security team
   • Created a new IngressClass with the ACM certificate, the WAF and access log settings
   • Added Ingresses for normal traffic, the admin screens and redirects, which restored routing

   Action items

   • Return to the CloudFront and VPC Origins layout while keeping a way to switch to internet-facing in code
   • Keep the internet-facing ALB, limited to approved CIDRs through spec.inboundCIDRs in IngressClassParams, so commenting out securityGroupInboundCidrs in values.yaml opens it to 0.0.0.0/0
   • Point the Terraform-managed Route53 A record back to CloudFront and keep the ALB alias commented out in code, so uncommenting and applying switches DNS to the ALB

   Lessons

   VPC Origins keeps the ALB off the internet and simplifies the traffic path, but it makes the service depend on an AWS-managed shared subsystem, and when that fails the service stops even though CloudFront is healthy. ANDPAD kept VPC Origins and instead prepared the escape route ahead of time, accepting the cost of an ALB that always runs, because recreating the Ingress and attaching it to the Rollout had taken so long during this incident.

   View case
2. IL-0542 Twingate authentication and authorization requests failed at higher rates after traffic moved onto a smaller GKE cluster

   Twingate2025

   Symptoms

   On 21 March 2025, between 21:10 and 21:41 UTC, part of the authentication and authorization requests to Twingate services failed with elevated error rates.

   High error rate

   Trigger

   Twingate saw anomalies in one of its GKE clusters and scaled down the deployments in that cluster to protect the rest of the system, which moved its traffic to the other clusters.

   Root cause

   Cloud provider outage

   Component

   Cloud load balancerGKE control planeHorizontal pod autoscalerCluster autoscaler

   Contributing factor

   Retry stormNo headroomOverlapping failuresHarmful manual action

   Detection

   Twingate observed anomalies in one of its GKE clusters at the start of the incident.

   Remediation

   • Reintroduced capacity in the cluster that had been scaled down, so traffic was rebalanced across regions

   Action items

   • Keep working with the cloud provider to find the cause of the unexpected timeouts and of the cluster update's impact
   • Run deployments in all regions with the same number of replicas in the HPA configuration
   • Raise the maximum node counts of the cluster node autoscalers to leave more room to scale up
   • Configure the HPA to scale up faster

   View case
3. IL-0446 About 20% of requests to an ITANDI ECS service got ALB 5XX errors, apparently from one zone, right after a deploy

   ITANDI2020

   Symptoms

   Right after a deploy to the production ECS (Fargate) service, HTTPCode_ELB_5XX_Count on the service's ALB jumped. The service receives about 10,000 requests a minute, and roughly 20% of them got a 5XX.

   High error rate

   Trigger

   A deploy recreated the ECS tasks, and at that moment communication between the ALB and its backends became unstable.

   Root cause

   Cloud provider outage

   Component

   Cloud load balancerAmazon ECS

   Contributing factor

   –

   Detection

   The team saw HTTPCode_ELB_5XX_Count jump on the ALB right after the deploy, together with target connection errors.

   Remediation

   • Restarted the ECS tasks, which did not help
   • Moved the ALB's ap-northeast-1d subnet to another subnet in the same zone, which did not help
   • Moved the six ECS tasks running in 1d to 1a and 1c, which did not help
   • Removed the 1d subnet from the ALB, which did not help
   • Changed the ALB idle timeout, which did not help
   • Rolled the ECS tasks back to the version before the deploy, which did not help
   • Created a new ALB with the same VPC, subnets, backends and security groups
   • Attached both ALBs to the ECS service
   • Sent one tenth of the traffic to the new ALB with a weighted DNS record
   • Moved all traffic to the new ALB after it returned no 5XX

   Lessons

   When a graph shows something that should be impossible on the network, suspect the AWS side as well.

   View case

By root cause1