Cases3 cases

1 to 3 of 3

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.

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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.

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3. 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

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