Cases4 cases

1 to 4 of 4

1. IL-0235 Azure OpenAI GPT-5.2 returned HTTP 400 in seven regions after a configuration update the model engine did not support

   Microsoft Azure2026

   Symptoms

   From 23:20 UTC on 9 March 2026 Azure OpenAI Service customers received HTTP 400 and HTTP 429 error responses for the GPT-5.2 model in Australia East, Central US, East US 2, Korea Central, Norway East, Sweden Central and UK South. All other GPT models kept working.

   High error rateLoad imbalance

   Trigger

   An update to the Azure OpenAI GPT-5.2 model enabled feature settings meant to improve service efficiency and resilience. The model engine version running in production did not yet support those settings. The update was rolled out to the whole fleet in stages under Safe Deployment Practices.

   Root cause

   Configuration change

   Component

   Model inference serverModel request routing

   Contributing factor

   Unrepresentative stagingMonitoring blind spotOverlapping failures

   Detection

   Service monitoring detected the issue at 00:19 UTC on 10 March, about an hour after impact began. Detection was late because monitoring was set up for client-side HTTP 400 errors and not for service-side anomalies.

   Remediation

   • Rolled back the GPT-5.2 configuration in all affected regions instead of waiting for a hotfix
   • Completed the routing updates and restored full regional capacity information so traffic was spread normally again

   Action items

   • Train engineers on the operating procedures, including which scenarios can be rolled back quickly
   • Store a cached known-good version of the traffic routing details for when the capacity service cannot provide current data
   • Set thresholds for service-side HTTP 400 errors in monitoring
   • Improve anomaly detection on HTTP 4xx errors to alert on unusual error rates below the usual thresholds
   • Add signals to the deployment systems so problematic rollouts stop automatically
   • Make sure early rollout stages have enough backend model instances to catch such problems

   View case
2. 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
3. IL-0407 Azure OpenAI returned 5xx errors in 14 of 28 regions after an automated cleanup deleted its GPU VMs and endpoints

   Microsoft Azure2024

   Symptoms

   From 00:00 UTC on 13 July 2024 a subset of Azure OpenAI (AOAI) customers got errors, such as 5xx responses, when calling their Azure OpenAI endpoints in 14 of the 28 regions that offer the service. Service monitoring saw failure rates cross their thresholds at 00:05 and alerted engineers.

   High error rateResources deleted

   Trigger

   A change to the global configuration file of the Azure OpenAI resource automation removed 14 resource groups that were thought to be unused, and the automation then deleted every resource in them.

   Root cause

   Configuration change

   Component

   Model inference serverAutomated capacity manager

   Contributing factor

   No staged rolloutNo safeguard on destructive changeUnverified assumption

   Detection

   Service monitoring detected failure rates above the defined thresholds at 00:05 UTC and alerted engineers, five minutes after impact began.

   Remediation

   • Stopped the automation that was running the cleanup
   • Added resource locks and blocked delete requests at the ARM and Automation levels
   • Recreated the deleted resources, rebuilding the service in parallel across the 14 regions
   • Manually reconfigured Azure Redis and Private Link for GPT-4o with the Azure Redis and Azure Networking teams
   • Manually restored DALL-E, adding the managed identity between its frontend and backend to an allowlist
   • Turned the automation back on on 15 July, which restored fine-tuning deployments

   Action items

   • Make the configuration policy regional and follow Safe Deployment Practices for all later configuration updates
   • Remove incorrect metadata tags on resources the automation must not manage and exclude them in the automation configuration
   • Concentrate the regional makeup of workloads in fewer regions
   • Improve the automation that engages incident response personnel
   • Investigate additional change management controls so that all production changes go through a gated safe deployment process (estimated completion August 2024)
   • Update the communications tooling with Azure OpenAI data so affected customers can be scoped and notified faster
   • Investigate additional test coverage and verification procedures to de-risk future configuration updates (estimated completion September 2024)
   • Add active monitoring for each model family that does not depend on customer traffic
   • Build out model pools with more parallelism to shorten recovery

   Lessons

   Microsoft names the missing safe deployment step as the main gap in its change management: a configuration change delivered as a global content update could not be rolled out region by region, so a single change caused a multi-region incident. Resource groups that mixed resources the automation managed with resources it did not know had let the automation's configuration drift from what actually existed in the production subscription.

   View case
4. IL-0533 Names in chinacloudapp.cn and chinacloudsites.cn stopped resolving as DNS caches expired, breaking Azure China services

   Microsoft Azure2024

   Symptoms

   From 03:45 CST on 23 April 2024, FQDNs in two system domains of Azure in China, chinacloudapp.cn and chinacloudsites.cn, gradually stopped resolving, and customers in the Azure China regions had trouble connecting to many Azure services and managing resources. Internal monitors alerted engineers to the degradation at 04:37 CST.

   DNS resolution failuresHigh error rateMonitoring outage

   Trigger

   At 03:45 CST a configuration change made through a domain registrar, as a step of a domain decommissioning workflow, updated the nameservers of chinacloudapp.cn and chinacloudsites.cn to a set of inactive servers.

   Root cause

   Configuration change

   Component

   Authoritative DNS servers and records

   Contributing factor

   Unverified assumptionCache-masked failure

   Detection

   Internal monitors alerted engineers to the degradation in the Azure China Cloud at 04:37 CST and created an incident, which the engineering team acknowledged at 04:39 CST.

   Remediation

   • Reverted the two domains to their previous working nameservers

   Action items

   • Suspended further runs of the domain lifecycle process until the management tool covers Azure in China
   • Make the validation process of domain lifecycle management include signals from all cloud regions
   • Add validations that get nameserver information by resolving the zone directly over the Internet

   View case

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