Cases2 cases

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1. IL-0339 Azure Front Door and Azure CDN users saw intermittent connection errors, timeouts and latency spikes for hours

   Microsoft Azure2024

   Symptoms

   From 11:45 UTC on 30 July 2024, a subset of customers got intermittent connection errors, timeouts and latency spikes when connecting to Microsoft services that use Azure Front Door (AFD) and Azure Content Delivery Network (CDN). The Azure Portal team saw the first service degradation at 11:47 UTC.

   Intermittent connection failuresIntermittent timeoutsHigh latencyPacket loss

   Trigger

   Around 11:45 UTC the Azure network DDoS protection service was disengaging after a routine DDoS mitigation and returning traffic to its default routing to AFD, but the routes at one site in Europe could not be updated because the network control plane could not reach that site during a local power outage.

   Root cause

   Configuration change

   Component

   CDN and edge networkDDoS protection serviceNetwork control plane (SDN)Data center power and cooling

   Contributing factor

   Overlapping failuresExcessive blast radiusMonitoring blind spot

   Detection

   The Azure Portal team detected service degradation at 11:47 UTC and began to investigate. At 12:10 UTC network monitoring correlated the Portal incident to a network issue at one site in Europe, and networking engineers joined.

   Remediation

   • Rerouted traffic under the standard congestion playbook, which removed most of the impact by 13:58 UTC
   • Ordered the network control plane to reissue its commands to the misbehaving device, which could not be reached
   • Removed the device that kept attracting traffic from the network and scanned the network for other issues

   Action items

   • Add the missing configuration on network devices so a DDoS mitigation issue in one geography cannot spread to another
   • Improve validation and monitoring in the Azure network to detect invalid configurations
   • Improve monitoring for when the DDoS protection service is unreachable from the control plane but still serving traffic

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2. IL-0258 FastMail was unreachable for almost two hours when the GRE tunnels carrying its traffic from Level 3 went down

   Fastmail2016

   Symptoms

   At 4.50am Melbourne time on Sunday 7 February (evening of 6 February UTC), FastMail became unavailable and stayed unreachable for almost two hours. Traffic to FastMail's public IP range never made it into FastMail's own network.

   Service outageNetwork unreachable

   Trigger

   The GRE tunnels between Level 3 and NYI, which carried FastMail's filtered traffic into its network, went down.

   Root cause

   Dependency failure

   Component

   DDoS protection serviceBGP routing

   Contributing factor

   Limited debug access

   Detection

   NYI, the datacentre provider, noticed the failure quickly.

   Remediation

   • NYI escalated with Level 3's support until FastMail's public IP ranges were pointed back to NYI

   Action items

   • Go back to DDoS protection from Black Lotus under NYI's explicit control
   • Build nginx frontends in the Los Angeles datacentre that reach NYI over the secondary network, and point DNS to them if NYI's primary network fails
   • Add hardware in Amsterdam and change the delivery system so it depends less on NYI
   • Work with NYI to understand its processes for detecting and responding to network faults

   Lessons

   Much of FastMail's and NYI's reliability had come from NYI controlling its own infrastructure. With protection always on at Level 3, NYI could not restore the routes itself, and FastMail calls the resulting delay in restoring service unacceptable.

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