Cloudflare incident on June 20, 2024

On Thursday, June 20, 2024, two independent events caused an increase in latency and error rates for Internet properties and Cloudflare services that lasted 114 minutes. During the 30-minute peak of the impact, we saw that 1.4 - 2.1% of HTTP requests to our CDN received a generic error page, and observed a 3x increase for the 99th percentile Time To First Byte (TTFB) latency.

These events occurred because:

1. Automated network monitoring detected performance degradation, re-routing traffic suboptimally and causing backbone congestion between 17:33 and 17:50 UTC
2. A new Distributed Denial-of-Service (DDoS) mitigation mechanism deployed between 14:14 and 17:06 UTC triggered a latent bug in our rate limiting system that allowed a specific form of HTTP request to cause a process handling it to enter an infinite loop between 17:47 and 19:27 UTC

Impact from these events were observed in many Cloudflare data centers around the world.

With respect to the backbone congestion event, we were already working on expanding backbone capacity in the affected data centers, and improving our network mitigations to use more information about the available capacity on alternative network paths when taking action. In the remainder of this blog post, we will go into Continue reading