Cases3 cases

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1. 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
2. IL-0549 Media, attachments, Git LFS and build artifacts failed for Atlassian in us-west-1 when an old network stack was removed

   Atlassian2023

   Symptoms

   From 02:36 UTC on 15 May 2023, Atlassian products with services hosted in the us-west-1 region could not store or retrieve data assets such as media, attachments and build artifacts. Automated monitoring detected it within three minutes, and the status page reported intermittent errors.

   High error rateStale endpoint routing

   Trigger

   An internal service was migrated to a new network segment as part of an initiative to harden the partitions between network segments, and the old network stack was then removed.

   Root cause

   Configuration change

   Component

   Authoritative DNS servers and records

   Contributing factor

   Unverified assumptionUnrepresentative staging

   Detection

   Automated monitoring detected the incident within three minutes.

   Remediation

   • Rolled back the network migration change, returning Atlassian systems to a known good state

   Action items

   • Review the systems that decommission service stacks and check that customer traffic is no longer served before a stack is decommissioned
   • Add steps to the service network migration process that identify associated DNS records needing attention

   Lessons

   Atlassian said the migration used blue/green deployment to limit this kind of risk, but adequate verification was not run before the old stack was decommissioned, and moving services between network segments is rare and hard to replicate in test.

   View case
3. IL-0351 Heroku apps in the EU and US had slow and failed requests as DNS round-robin sent traffic to single router hosts

   Heroku2017

   Symptoms

   Between 3 and 7 June 2017, Heroku customers in both the EU and US regions had periods of high latency: some requests failed and others took an excessive time to pass through the Heroku Routing Layer. All customers in the EU and US were affected at various times.

   High latencyHigh error rateLoad imbalance

   Root cause

   DNS or network fault

   Component

   Authoritative DNS servers and recordsCloud load balancer

   Contributing factor

   Unverified assumption

   Remediation

   • Found the sources of high-volume traffic and worked with those apps' owners to distribute their requests better
   • Replaced the legacy DNS records with new, corrected DNS records

   Action items

   • Make monitoring alert engineers sooner to unevenly distributed traffic
   • Investigate how to configure DNS and load balancers to reduce the effect of high-volume and bursting traffic
   • Work with caching Add-on partners on the DNS configuration issues that affect them, to achieve proper load balancing

   View case

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