Cases3 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-0257 canva.com went down for about 50 minutes when 1.5 million requests per second OOM-killed every API Gateway task

   Canva2024

   Symptoms

   On 12 November 2024, after a new version of Canva's editor was deployed at 8:47 AM UTC, the editor's object panel stayed in a perpetual loading state for many users, particularly in Asia. Then from 9:08 AM UTC to about 10:00 AM UTC canva.com was unavailable and all requests to it failed.

   Service outageOOMKilledHigh latencyPacket loss

   Trigger

   At 8:47 AM UTC a new version of the Canva editor page was deployed, and client devices began fetching its new static assets through Cloudflare while the network path between Cloudflare's Singapore and Ashburn locations was losing packets.

   Root cause

   Dependency failure

   Component

   CDN and edge networkAPI gatewayAmazon ECS

   Contributing factor

   Overlapping failuresMonitoring blind spotRetry stormAutomation amplificationUnpatched known bug

   Remediation

   • Added a temporary Cloudflare firewall rule at 9:29 AM UTC that blocked all traffic at the CDN so new API Gateway tasks could start
   • Redirected canva.com to the status page
   • Restored traffic gradually, starting with Australian users under strict rate limits

   Action items

   • Write a runbook for rerouting, blocking and progressively restoring traffic
   • Show users a more informative error page when canva.com is unavailable
   • Raise the baseline number of API Gateway tasks and the memory of each task
   • Add load shedding rules to the API Gateway for similar traffic patterns
   • Load test the API Gateway regularly
   • Deploy the patch for the thread-locking bug in the telemetry library
   • Add multithreaded tests for the contended code path to the telemetry library microbenchmark suite
   • Use page load completion events as a second canary indicator for page asset releases
   • Experiment with adding another rollout stage to the canary to give more time to detect issues
   • Add timeouts so user requests do not wait excessively long for assets
   • Work with Cloudflare to understand the system interactions behind the incident

   View case
3. IL-0388 A Google Cloud live migration took a Discord Redis primary offline, and the failover broke API instances and then guilds

   Discord2017

   Symptoms

   At about 14:01 PDT on 13 October 2017, Discord engineers were alerted to anomalies by real-time metrics and monitoring. A Redis instance that was the primary of a highly available cluster used by the API services had dropped offline after Google Cloud Platform migrated it automatically, and some API instances did not handle the failover to the secondary node correctly.

   Failover failureHigh latencyService outage

   Trigger

   Google Cloud Platform automatically migrated the Redis instance that was the primary of a highly available cluster used by the API services, and the node incorrectly dropped offline.

   Root cause

   Software defect

   Component

   In-memory cacheDatabaseCDN and edge network

   Contributing factor

   Unpatched known bugOverlapping failuresMonitoring blind spot

   Detection

   Real-time metrics and monitoring alerted engineers at 14:01 PDT. The second phase was seen at 15:41 as another anomaly in monitoring, and end user reports of servers appearing offline were escalated at 15:42.

   Remediation

   • Ran a rolling restart of all API instances to clear the Redis connection issues
   • Corrected the misconfigured edge caching rule for the expensive API route
   • Disabled the problem API endpoint on the edge network
   • Recovered the Cassandra cluster
   • Ran a second rolling restart of all API instances for the latency left by the Cassandra issues
   • Removed the misbehaving guilds node from the service hashring
   • Forcefully restarted the misbehaving guilds node
   • Restarted the whole service, forcing all users to reconnect
   • Blocked traffic that relied on the failing push component to reduce its load
   • Corrected the API setting that lets users reconnect quickly and safely

   Action items

   • Fix the known issues with Redis failover within the coming weeks
   • Change the cached route so this type of error does not degrade other services
   • Monitor the signals that would have warned of the cascading failure
   • Improve the reliability and failure handling of the affected services
   • Roll out an update of the library with the suspected flaws

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