Incident Library
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  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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Configuration change1 case

Component
CDN and edge networkcert-managerAuthoritative DNS servers and records
Contributing factor
Change with a delayed effectMonitoring blind spotNo configuration tests
Organisation
MIT Open Learning
  1. IL-0512 xpro.mit.edu returned 503 for an hour when its Kubernetes/APISIX origin certificate expired after renewal failed
    MIT Open Learning2026