Incident Library
  • Root cause
  • Component
  • Symptom
  • Contributing factor
  • Case

Cases6 cases

1 to 5 of 6

  1. IL-0512 xpro.mit.edu returned 503 for an hour when its Kubernetes/APISIX origin certificate expired after renewal failed
    MIT Open Learning2026sev1
    Symptoms

    At 3:38 PM EDT on 3 June 2026, alerts fired because both the xPRO production CMS and the main xPRO site at https://xpro.mit.edu were returning 503 errors. Fastly, in front of the site, could not connect to the Kubernetes/APISIX origin, because the origin certificate for xpro-web.odl.mit.edu had expired at 3:29 PM EDT.

    Service outageTLS certificate errors
    Trigger

    The origin certificate xpro-cert for xpro-web.odl.mit.edu, issued on 2026-03-05 with a 90-day validity period, expired at 3:29 PM EDT on 3 June 2026.

    Root cause
    Configuration change
    Component
    cert-managerCDN and edge networkAuthoritative DNS servers and records
    Contributing factor
    No configuration testsMonitoring blind spotChange with a delayed effect
    Detection

    Alerts for the xPRO production CMS and the main xPRO site fired at 3:38 PM EDT on the 503 errors, and a Rootly incident was created at 4:08 PM EDT.

    Remediation
    • Deleted and recreated the stale cert-manager certificate resources so that cert-manager issued a fresh origin certificate
    Action items
    • Remove the backend origin domain from the non-OpenEdX xPRO Fastly TLS subscription, so Fastly manages only xpro.mit.edu
    • Deploy the Pulumi update for the xPRO application in Production
    • Trigger cert-manager renewal of the xPRO certificate after the conflicting Fastly validation CNAME is removed
    • Consider tests or policy checks that keep cert-manager-managed origin domains out of Fastly TLS subscriptions
    • Consider alerting earlier on failed cert-manager CertificateRequests and Orders, so stale ACME failures are found before the certificate expires
    Lessons

    Reading the outage as a failed cert-manager ACME renewal was true but incomplete; the missing part was that Fastly had been set to manage validation for a backend origin domain that belonged to cert-manager. The team concluded that TLS certificates and DNS validation records need guardrails around ownership, and that public Fastly frontend domains and Kubernetes/APISIX origin domains must not be treated as interchangeable service domains in TLS automation.

    View case
  2. IL-0502 The JupyterHub at temple.2i2c.cloud stopped resolving in DNS after a wildcard record was added for a new cluster
    2i2c2025
    Symptoms

    On 20 August 2025 at 10:02 AM Pacific time, an automated uptime check on temple.2i2c.cloud started failing and paged 2i2c: the JupyterHub at temple.2i2c.cloud could not be reached, shortly before the community that uses it was to give a demo.

    DNS resolution failuresService outage
    Trigger

    At 9:21 AM, while setting up a new cluster for Temple, a wildcard DNS record *.temple.2i2c.cloud was added pointing to the new cluster's Ingress IP.

    Root cause
    Configuration change
    Component
    Authoritative DNS servers and records
    Contributing factor
    Unverified assumptionCache-masked failureUnreviewed defaults
    Detection

    Automated uptime alerts caught the failure at 10:02 AM, before the community reported it in a support ticket at 10:09 AM.

    Remediation
    • Added an explicit A record for temple.2i2c.cloud in Namecheap
    • Lowered the DNS TTL from the 30-minute default to 5 minutes
    • Offered the community member running the demo an /etc/hosts entry as a workaround
    Action items
    • Give everyone on the team access to Namecheap, or move to another DNS provider
    • Use a 5-minute TTL instead of 30 minutes for all new DNS entries
    • Document that adding a *.X.2i2c.cloud DNS entry requires adding an X.2i2c.cloud entry as well
    Lessons

    Adding a wildcard record for a subdomain stopped a broader wildcard from answering for that subdomain's own name, so a *.X.2i2c.cloud record needs an X.2i2c.cloud record alongside it. The 30-minute default TTL at Namecheap meant any DNS fix could take that long to propagate, and the engineer creating the original record had no access to the DNS provider.

    View case
  3. 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
  4. IL-0254 Square's internal DNS servers failed and Square products, services and payments were unavailable for about 15 hours
    Square2023
    Symptoms

    From 1:54 PM ET on 7 September 2023, Square products and services were unavailable, and at 2:02 PM ET engineers were notified of infrastructure issues and began investigating DNS. Square Online websites stayed up, but their customers could not make payments.

    DNS resolution failuresService outage
    Trigger

    At 11:04 AM ET a host-based firewall rule change was deployed to enable region communication, which increased the size of the firewall rules on nodes. Combined with a DNS service upgrade, it put unexpected load on the internal DNS servers. The timeline also lists a DNS zone change at 1:56 PM ET.

    Root cause
    Configuration change
    Component
    Authoritative DNS servers and recordsNode iptables rules
    Contributing factor
    No staged rolloutCache-masked failureCircular dependency
    Detection

    Engineers were notified of infrastructure issues at 2:02 PM ET, eight minutes after services became unavailable.

    Remediation
    • Shed network traffic to the DNS servers and started bringing up new DNS servers by hand
    • Deployed networking changes by hand to re-enable the authorization and access services
    • Deployed the networking changes by hand to all data centers
    • Rebuilt the DNS servers
    • Built a new configuration from the reverted firewall ruleset and pushed it to the DNS hosts
    Action items
    • Move the DNS infrastructure onto isolated infrastructure
    • Add monitoring and optimizations for critical networking infrastructure
    • Optimize dependencies between the deploy and platform infrastructure where feasible
    • Expand support for Offline Mode and improve communication about when it is available
    View case
  5. 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
Check your cluster for this

These 6 cases involve Authoritative DNS servers and records and CDN and edge network. kubegap audits a Kubernetes cluster for gaps like these, read-only, from Claude Code or Codex; its checks cite public reports like the ones in this library.

Open kubegap

By root cause1

Configuration change6 cases

Component
Authoritative DNS servers and records6CDN and edge network2cert-manager1Node iptables rules1Terraform1
Contributing factor
Unverified assumption3Cache-masked failure3Unrepresentative staging2Circular dependency1Unreviewed defaults1Change with a delayed effect1Monitoring blind spot1No configuration tests1No safeguard on destructive change1No staged rollout1
Organisation
2i2c1Atlassian1Microsoft Azure1MIT Open Learning1Rust Project1Square1
  1. IL-0512 xpro.mit.edu returned 503 for an hour when its Kubernetes/APISIX origin certificate expired after renewal failed
    MIT Open Learning2026
  2. IL-0502 The JupyterHub at temple.2i2c.cloud stopped resolving in DNS after a wildcard record was added for a new cluster
    2i2c2025
  3. IL-0533 Names in chinacloudapp.cn and chinacloudsites.cn stopped resolving as DNS caches expired, breaking Azure China services
    Microsoft Azure2024
  4. IL-0254 Square's internal DNS servers failed and Square products, services and payments were unavailable for about 15 hours
    Square2023
  5. IL-0549 Media, attachments, Git LFS and build artifacts failed for Atlassian in us-west-1 when an old network stack was removed
    Atlassian2023
  6. IL-0363 static.crates.io did not resolve for 10-15 minutes during a Terraform deployment, so Rust builds could not fetch crates
    Rust Project2023