Cases2 cases

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1. IL-0283 Cloudflare's core proxy returned HTTP 5xx across its network after loading an oversized Bot Management feature file

   Cloudflare2025

   Symptoms

   From about 11:20 UTC on 18 November 2025, Cloudflare's network started failing to deliver core traffic, and Internet users visiting Cloudflare customers' sites got an error page that pointed to a failure inside Cloudflare's network. The volume of HTTP 5xx responses served by the network jumped far above its normal low baseline.

   High error rateService outageHigh latencyResponse quality degradation

   Trigger

   At 11:05 UTC Cloudflare deployed a ClickHouse access control change that made users' existing implicit access to the underlying tables in the r0 database explicit, so the metadata of those tables became visible in system tables such as system.columns. The change was being rolled out gradually across the cluster.

   Root cause

   Configuration change

   Component

   DatabaseCDN and edge network

   Contributing factor

   Unverified assumptionPartial rolloutNo staged rolloutNo configuration testsOverlapping failuresRetry storm

   Detection

   The first automated test detected the issue at 11:31 UTC, three minutes after the first errors on customer HTTP traffic at 11:28. Manual investigation started at 11:32 and the incident call was created at 11:35.

   Remediation

   • Bypassed the core proxy for Workers KV and Access so they fell back to a prior proxy version, which reduced their impact
   • Stopped the automatic creation and deployment of new Bot Management feature files
   • Inserted a known good feature file into the distribution queue and deployed it globally
   • Forced a restart of the core proxy
   • Scaled control plane concurrency to clear the backlog of dashboard logins
   • Restarted the remaining services that had entered a bad state

   Action items

   • Harden the ingestion of Cloudflare-generated configuration files the same way as user-generated input
   • Enable more global kill switches for features
   • Stop core dumps and other error reports from being able to overwhelm system resources
   • Review the failure modes for error conditions across all core proxy modules

   View case
2. IL-0284 Workers KV failed 90.22% of requests in a third-party storage outage, breaking Access, WARP and many Cloudflare products

   Cloudflare2025

   Symptoms

   At 17:52 UTC on 12 June 2025, Cloudflare's WARP team saw registrations of new devices failing and declared an incident. Minutes later the Cloudflare Access team got an alert on a rapid rise in error rates, and Service Level Objectives for several other services fell below target. All of them shared one cause: Workers KV was unavailable.

   High error rateService outageCredentials unavailable

   Trigger

   Part of the storage infrastructure behind Workers KV is backed by a third-party cloud provider, and that provider had an outage. Workers KV could then no longer serve cold reads or writes from its central data store.

   Root cause

   Cloud provider outage

   Component

   Database

   Contributing factor

   Single point of failureExcessive blast radiusCircular dependencyRetry storm

   Detection

   The WARP team saw registrations of new devices failing at 17:52 UTC and declared an incident. At 18:05 the Access team received an alert on a rapid increase in error rates and Service Level Objective alerts fired across several teams; at 18:06 the incidents were combined once Workers KV unavailability was identified as the shared cause.

   Remediation

   • Activated the Challenges and Turnstile kill switches so visitors were not blocked
   • Degraded Gateway rules that referenced identity or device posture state to remove the Workers KV dependency
   • Force-dropped Access identity and device posture requests to shed load on Workers KV
   • Worked on a Workers KV release against an alternative backing datastore in case the storage stayed down
   • Restored Access and Device Posture calls to Workers KV once the third-party service was back

   Action items

   • Avoid singular dependencies on storage infrastructure that Cloudflare does not own
   • Improve the ability to recover critical services, including Access, Gateway and WARP
   • Add redundancy to Workers KV's storage infrastructure and remove the dependency on any single provider
   • Make each affected product resilient to the loss of any single point of failure, third-party dependencies included
   • Build tooling to re-enable namespaces progressively during storage incidents, so services come back without overloading Cloudflare's own infrastructure

   Lessons

   Cloudflare holds itself responsible for its choice of dependencies and how it architects around them, even when a vendor failure was the trigger. Building many products on Workers KV normally makes them more robust than separate storage services would, but here the cascading failure of Workers KV made the outage worse and widened its blast radius.

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