Cases6 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

   View case
2. IL-0522 An ingress-nginx chart upgrade deleted the jenkins.io Ingress and Fastly served HTTP/503 errors for hours

   Jenkins project2021

   Symptoms

   At 11:32 UTC on 18 November 2021, a user reported in the jenkinsci/jenkins Gitter channel that https://www.jenkins.io/doc/pipeline/steps/ was answering HTTP/503 errors with the message "Guru meditation" from Fastly's varnish.

   Service outageResources deleted

   Trigger

   The ingress-nginx Helm chart was upgraded from 4.0.6 to 4.0.8 at 10:42 UTC, and the new chart added an admission webhook rule that forbids Nginx configuration blocks in Ingress annotations.

   Root cause

   Breaking change in an upgrade

   Component

   Ingress controllerAdmission webhookHelmCDN and edge network

   Contributing factor

   Unverified assumptionCache-masked failureMonitoring blind spotHarmful manual action

   Detection

   A user reported in the jenkinsci/jenkins Gitter channel at 11:32 UTC that a jenkins.io page answered HTTP/503 errors, and status.jenkins.io reported the incident at 11:49 UTC.

   Remediation

   • Disabled the automated systems, rolled the ingress-nginx chart back to 4.0.6 and deleted the admission webhook by hand
   • Removed the forbidden annotations from the jenkins.io configuration
   • Upgraded the jenkins.io Helm chart to the last version known to work with ingress-nginx 4.0.8
   • Redeployed the jenkins.io Helm chart through the automated system and told Fastly to drop all cached pages

   Action items

   • Always read the changelog in depth when updating the ingress controllers, with two people pairing in real time
   • Add custom Datadog monitoring for www.origin.jenkins.io so that such an outage is detected
   • Make the monitor send the Host header www.jenkins.io so it is not redirected to Fastly
   • Check a set of pages, such as the pipeline steps page, not only the front page
   • Consider an ephemeral k3s end-to-end test before deploying to production

   Lessons

   Trusting a patch version of a Helm chart for the Ingress controller without reading its changelog in depth let a new admission rule remove the jenkins.io Ingress in production. Without monitoring on origin.jenkins.io, a user found the outage. A complete staging cluster with the same DNS setup would have caught the problem before production.

   View case
3. IL-0491 Squarespace's CDN origin fleet fell below its healthy node threshold, and images, scripts and stylesheets failed to load

   Squarespace2019

   Symptoms

   At 12:10 AM ET on Tuesday, February 12, 2019, Squarespace's monitoring alerted the on-call engineer for the CDN origin fleet that the fleet had fallen below a safe number of healthy nodes. Requests to static.squarespace.com and static1.squarespace.com failed, so images, scripts and style sheets did not load for some sites, and the status page later reported elevated error rates serving media and stylesheets.

   High error rate

   Trigger

   At 10:30 PM ET on February 11, an engineer started a maintenance operation across the CDN origin fleet. The operation kept running in the background after the engineer believed it had been terminated.

   Root cause

   Operator error

   Component

   CDN and edge network

   Contributing factor

   Excessive blast radiusMonitoring blind spot

   Detection

   The monitoring system alerted the CDN origin fleet's on-call engineer at 12:10 AM ET when the fleet fell below a safe number of healthy nodes.

   Remediation

   • Restored the CDN origin fleet, partially by 2:15 AM ET and to normal behaviour at 2:20 AM ET

   Action items

   • Revise the incident-response playbooks with checks and actions for this fleet, starting with an assessment of customer impact and the immediate involvement of an Incident Commander
   • Improve external monitoring to assess customer impact of issues with the CDN partners and origin services more quickly
   • Revise operational policies and add safeguards for issuing maintenance commands, including limiting the share of the fleet a command can operate on
   • Reduce the need for direct manual maintenance operations
   • Create independent failure domains and route requests automatically around unhealthy parts of the system

   View case
4. IL-0388 A Google Cloud live migration took a Discord Redis primary offline, and the failover broke API instances and then guilds

   Discord2017

   Symptoms

   At about 14:01 PDT on 13 October 2017, Discord engineers were alerted to anomalies by real-time metrics and monitoring. A Redis instance that was the primary of a highly available cluster used by the API services had dropped offline after Google Cloud Platform migrated it automatically, and some API instances did not handle the failover to the secondary node correctly.

   Failover failureHigh latencyService outage

   Trigger

   Google Cloud Platform automatically migrated the Redis instance that was the primary of a highly available cluster used by the API services, and the node incorrectly dropped offline.

   Root cause

   Software defect

   Component

   In-memory cacheDatabaseCDN and edge network

   Contributing factor

   Unpatched known bugOverlapping failuresMonitoring blind spot

   Detection

   Real-time metrics and monitoring alerted engineers at 14:01 PDT. The second phase was seen at 15:41 as another anomaly in monitoring, and end user reports of servers appearing offline were escalated at 15:42.

   Remediation

   • Ran a rolling restart of all API instances to clear the Redis connection issues
   • Corrected the misconfigured edge caching rule for the expensive API route
   • Disabled the problem API endpoint on the edge network
   • Recovered the Cassandra cluster
   • Ran a second rolling restart of all API instances for the latency left by the Cassandra issues
   • Removed the misbehaving guilds node from the service hashring
   • Forcefully restarted the misbehaving guilds node
   • Restarted the whole service, forcing all users to reconnect
   • Blocked traffic that relied on the failing push component to reduce its load
   • Corrected the API setting that lets users reconnect quickly and safely

   Action items

   • Fix the known issues with Redis failover within the coming weeks
   • Change the cached route so this type of error does not degrade other services
   • Monitor the signals that would have warned of the cascading failure
   • Improve the reliability and failure handling of the affected services
   • Roll out an update of the library with the suspected flaws

   View case

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