Incident Library
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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-0341 Traffic between Cloudflare and AWS us-east-1 had high latency, packet loss and origin failures for almost four hours
    Cloudflare2025
    Symptoms

    From 16:27 UTC on 21 August 2025, users connecting to Cloudflare from servers in AWS us-east-1, or receiving connections from Cloudflare there, saw high latency, packet loss and failures to reach origins. Cloudflare's network team was alerted to internal congestion in Ashburn (IAD) at 16:44 UTC.

    Packet lossHigh latencyIntermittent timeouts
    Trigger

    At about 16:27 UTC a single customer began sending many requests from AWS us-east-1 to Cloudflare for objects in Cloudflare's cache, doubling the total traffic from Cloudflare to AWS.

    Root cause
    Capacity exhaustion
    Component
    Transit gateway or network interconnectBGP routingCDN and edge network
    Contributing factor
    No headroomHarmful manual actionExcessive blast radius
    Detection

    Cloudflare's network team was alerted to internal congestion in Ashburn (IAD) at 16:44 UTC, and an incident was raised for customer impact at 17:45 UTC.

    Remediation
    • Rate limited the single customer whose traffic caused the surge
    • Took further traffic engineering actions that fully resolved the congestion
    • Asked AWS to revert its BGP prefix withdrawals, which AWS finished at 20:07 UTC
    Action items
    • Build a mechanism to deprioritise a customer's traffic when it congests the network enough to affect others
    • Speed up the Data Center Interconnect upgrades to add network capacity
    • Work with AWS so the two companies' BGP traffic engineering actions do not conflict
    • Build a traffic management system that gives each customer a network resource budget and automates the manual actions used here
    Lessons

    Cloudflare concludes that it must isolate customers better so that no single customer can take over shared network resources and degrade the platform for others, and that its network needs enough capacity to meet demand. It describes the outage as the result of insufficient network congestion management during an unusual high-traffic event.

    View case
Check your cluster for this

These 2 cases involve CDN and edge network and BGP routing. 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.

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By root cause2

Configuration change1 case

Component
CDN and edge networkDatabase
Contributing factor
Unverified assumptionNo configuration testsNo staged rolloutOverlapping failuresPartial rolloutRetry storm
Organisation
Cloudflare
  1. IL-0283 Cloudflare's core proxy returned HTTP 5xx across its network after loading an oversized Bot Management feature file
    Cloudflare2025

Capacity exhaustion1 case

Component
BGP routingCDN and edge networkTransit gateway or network interconnect
Contributing factor
Excessive blast radiusHarmful manual actionNo headroom
Organisation
Cloudflare
  1. IL-0341 Traffic between Cloudflare and AWS us-east-1 had high latency, packet loss and origin failures for almost four hours
    Cloudflare2025