Cases2 cases

1 to 2 of 2

1. IL-0248 Azure OpenAI inference requests slowed and failed in several regions as a retry storm overloaded the routing layer

   Microsoft Azure2026

   Symptoms

   From 09:39 to 17:05 UTC on 29 May 2026, customers sending inference requests to Azure OpenAI Service saw higher latency, intermittent failures, timeouts and HTTP 5XX errors. Automated monitoring detected falling request success rates at 09:39 UTC, and regions in Europe and Australia East, which processed the most affected traffic, were hit hardest.

   High latencyHigh error rateIntermittent timeoutsOOMKilled

   Trigger

   A change in an upstream API layer used by Microsoft 365 made some capacity-related failures surface as transient server failures that callers retry. It rolled out first in Australia East and later in Sweden Central.

   Root cause

   Faulty deployment

   Component

   Model request routing

   Contributing factor

   Retry stormExcessive blast radiusUnverified assumption

   Detection

   Automated monitoring detected a drop in request success rates at 09:39 UTC and started the incident investigation.

   Remediation

   • Isolated the internal workload that sent the amplified retries onto dedicated infrastructure
   • Rolled back the triggering change in the upstream service and reduced retry-driven traffic
   • Cleared the backlogged requests

   Action items

   • Move large first-party generative AI workloads onto dedicated routing infrastructure instead of the shared inference load balancing stamp
   • Improve diagnostic guidance, runbooks and alerting to tell secondary crash symptoms from the real source of overload
   • Work with upstream teams on retry policy design, dependency contracts and telemetry to catch retry amplification early
   • Add stronger overload prevention and throttling so no single internal workload can overwhelm shared components
   • Find and remove single points of failure in the inference routing layer

   Lessons

   Internal workloads were not protected the way external traffic was: their traffic skipped some rate limiting and overload controls, so the amplified retries reached shared infrastructure. The apparent recovery after disabling the suspected feature hid the real cause until the problem came back at larger scale in Sweden Central.

   View case
2. IL-0225 An IGP purge command made every Microsoft WAN router recompute routes, causing global latency, timeouts and packet loss

   Microsoft Azure2023

   Symptoms

   From 07:08 UTC on 25 January 2023, customers saw long network latency and timeouts when connecting to resources in Azure regions and to other Microsoft services such as Microsoft 365 and Power Platform. Microsoft's monitoring detected DNS and WAN issues from 07:11 UTC.

   High latencyIntermittent timeoutsIntermittent connection failuresPacket lossNetwork unreachable

   Trigger

   A network engineer adding capacity to the global WAN in Madrid ran a step of a recently changed standard operating procedure that purged the IGP database; on the router manufacturer involved, that command runs on all IGP-joined routers instead of only the local one.

   Root cause

   Configuration change

   Component

   Backbone network (WAN)Interior routing (IGP)BGP routing

   Contributing factor

   No configuration testsUnverified assumptionExcessive blast radiusHarmful manual action

   Detection

   Monitoring detected DNS and WAN issues from 07:11 UTC and alerted the on-call engineers within 5 minutes of the command being run. The team reviewed all recent changes and identified the command by 08:20 UTC. The engineer making the change was not informed of the alerts because of the unqualified changes to the SOP.

   Remediation

   • Restarted by hand the paused WAN health and traffic engineering systems, which ended the remaining packet loss

   Action items

   • Audit and block similar widespread-impact commands across all three vendors for all WAN router roles
   • Give on-call engineers real-time visibility of approved and unqualified activity on network devices
   • Run regular mandatory operational training and attestation of following all SOPs
   • Have the Change Advisory Board review all SOPs still pending qualification within 30 days

   View case

By root cause2