Cases2 cases

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1. IL-0150 A latent race condition in DynamoDB's DNS automation left an empty DNS record for dynamodb.us-east-1.amazonaws.com, and the DynamoDB and EC2 launch failures that followed caused EKS, ECS and Fargate container launch failures and cluster scaling delays in us-east-1

   Amazon Web Services2025

   Symptoms

   At 11:48 PM PDT on 19 October 2025, every system that reached DynamoDB in us-east-1 through the public regional endpoint started getting DNS failures and could not connect. This included customer traffic and internal AWS services that depend on DynamoDB. DynamoDB global table replicas in other regions still answered but fell behind in replication to and from us-east-1.

   DNS resolution failuresHigh error rateScale-up failureIntermittent connection failuresHigh latency

   Trigger

   One DNS Enactor, slowed by unusually high retry delays, applied a much older DNS plan to the regional DynamoDB endpoint just as another Enactor that had applied the newest plan ran its clean-up, which deleted that older plan and with it every IP address of the endpoint.

   Root cause

   Software defect

   Component

   Authoritative DNS servers and recordsApplication databaseCloud load balancer

   Contributing factor

   Automation amplificationRetry stormNo runbook

   Detection

   DNS failures to DynamoDB began immediately at 11:48 PM PDT and the engineering teams of affected AWS services were engaged at once; by 12:38 AM they had identified DynamoDB's DNS state as the source. The later NLB health check problem was detected by monitoring at 6:52 AM.

   Remediation

   • applied temporary mitigations by 1:15 AM that let some internal services reach DynamoDB and repaired key internal tooling
   • restored all DynamoDB DNS information by 2:25 AM through manual operator intervention
   • throttled incoming work and selectively restarted DWFM hosts from 4:14 AM so droplet leases could be re-established
   • reduced the load on Network Manager to bring network configuration propagation times back to normal by 10:36 AM
   • disabled automatic health check failover for NLB at 9:36 AM, and re-enabled it at 2:09 PM after EC2 recovered
   • relaxed the EC2 request throttles from 11:23 AM until all EC2 APIs and launches were normal at 1:50 PM

   Action items

   • Disable the DynamoDB DNS Planner and DNS Enactor automation worldwide
   • Fix the race condition and add protections against applying incorrect DNS plans before re-enabling the DNS automation
   • Add a velocity control to NLB that limits how much capacity a single load balancer can remove when health check failures cause availability zone failover
   • Build an additional EC2 test suite that exercises the DWFM recovery workflow at scale
   • Improve throttling in EC2 data propagation systems so incoming work is rate limited by the size of the waiting queue

   Lessons

   A single DNS record that automation can empty is enough to take a widely used regional endpoint off the network, and every service built on it fails in turn. A check made once at the start of a long operation can be stale by the time the operation writes its result. Recovery of the dependency is not recovery of the dependents: systems that lost state during the outage, such as EC2's droplet leases and network propagation backlog, can collapse under their own catch-up work, and container services that rely on new instance launches keep failing to launch and scale until that work is done.

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2. IL-0131 A new kind of GenerateContent request made Vertex AI prediction API servers segfault, and once enough of them restarted at the same time the serving fleet could not carry the load

   Google Cloud2024

   Symptoms

   From 12:06 US/Pacific on 12 June 2024, services built on Vertex AI Prediction began reporting failed user requests in eight regions: us-central1, asia-southeast1, europe-west3, europe-west4, us-east1, us-west1, northamerica-northeast1 and us-east4.

   High error rateHigh latencyIntermittent timeouts

   Trigger

   Starting on 8 June 2024, a new form of user request to the GenerateContent API caused intermittent segmentation faults in the Vertex Serving Prediction API servers; on 12 June the rate of such requests increased.

   Root cause

   Software defect

   Component

   Model inference serverCloud load balancer

   Contributing factor

   Partial rolloutNo headroom

   Detection

   Internal production monitoring alerted engineers to the segfaults on 10 June 2024 at 07:35 US/Pacific, before any visible customer impact; on 12 June services built on Vertex Prediction reported failing user requests.

   Remediation

   • confirmed the new failures came from the same segfault found on 10 June
   • accelerated the rollout of the fix that was already in progress, completed at 15:59 US/Pacific

   Action items

   • Ensure early signals of server binary issues are captured in production health analysis and investigated in time
   • Ensure release validation of feature changes and updates in production

   Lessons

   A crash that only some requests trigger can stay invisible while load balancers route around the restarting servers. It becomes an outage when the share of such requests grows until too many servers are restarting at once. Here the cause was known and a fix was rolling out two days before customers were affected, but the progressive rollout had not finished when the triggering traffic increased; Google's follow-up is to investigate early signals of server binary issues in time.

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