Cloudflare Outage – June 21, 2022

Incident Overview

On June 21, 2022, a major outage at Cloudflare — one of the largest CDN (Content Delivery Network) and internet security providers — knocked out access to dozens of popular websites like Shopify, Discord, Canva, Feedly, and NordVPN. For nearly 90 minutes, users around the world saw 500 Internal Server Errors, unable to access essential services.

At the core of this chaos? A botched network configuration during a data center migration — proving once again how fragile and interconnected the web truly is.

Timeline of the Incident

Technical Breakdown

What Went Wrong?

Cloudflare was performing a planned migration of core traffic away from legacy data centers to a new, more performant architecture known as "Multi-Colo PoP" (MCP).

As part of this migration, a configuration change was applied to the BGP routing and firewall policy inside multiple data centers. This change inadvertently rerouted too much traffic through limited CPU resources, overwhelming the core routing infrastructure.

Specific Technical Issues

• Improper CPU Pinning: The change unintentionally allowed BGP and firewall rules to consume CPU cycles meant for HTTP/HTTPS routing.

• Spillover Effect: Overloaded CPUs delayed or dropped requests, leading to 500 Internal Server Errors.

• Looped Traffic: In some edge locations, misconfigured policies caused routing loops, amplifying network congestion.

Incident Management Breakdown

Detection

• Internal metrics from Cloudflare Radar and Prometheus showed sudden drops in throughput and spiking latencies.

• External platforms like ThousandEyes and Downdetector confirmed worldwide access failures.

• Synthetic traffic monitors began failing health checks in >19 data centers simultaneously.

Initial Triage

• SEV-1 declared and all regional SRE and network engineering teams pulled into a bridge.

• Engineers quickly narrowed the issue to new BGP policies and firewall behaviors rolled out as part of the migration.

• Incident command switched to regional isolation mode — rerouting critical internal tools away from affected PoPs.

Root Cause Identification

• Review of the Git-based configuration deployment history pinpointed a problematic change to policy configuration files affecting CPU allocation.

• Packet inspection and system logs confirmed the routing table was being excessively queried, causing CPU starvation in key edge routers.

Mitigation & Recovery

• Engineers performed a phased rollback of the configuration across all affected data centers.

• Temporary CPU throttling and traffic shedding were introduced in hotspots to stabilize service during rollback.

• After rollback, internal routing tables rebalanced and latency normalized across all endpoints.

Closure

• Full restoration confirmed by 08:50 UTC.

• Cloudflare published a highly detailed post-incident analysis, including BGP map snapshots, CPU metrics, and architectural diagrams.

• Internal reviews triggered reforms in change management workflows and staged deployment strategies.

Business Impact

• Websites Affected: Discord, Canva, Shopify, NordVPN, Feedly, Crypto.com, and hundreds more.

• Services Disrupted: CDN delivery, DNS resolution, API gateways, and WAF (Web Application Firewall) protection.

• Customer Impact: Lost transactions, service reputation issues, and user frustration across industries.

• Downtime Duration: ~1 hour 23 minutes (varied by region).

Lessons Learned (for IT Professionals)

Treat Network Configs Like Code

Network engineers must follow version control, code reviews, and test pipelines — the same way developers treat application code.

Simulate Edge Failures

Cloudflare's incident revealed the need to simulate extreme edge behaviors, especially during multi-data center migrations.

Protect the Control Plane

Critical infrastructure (like the routing control plane) must have reserved CPU, memory, and process isolation to ensure it doesn't get starved during routing storms.

Use Staged Deployments

High-risk changes should follow a canary-first rollout model — test in a few regions, monitor impacts, then expand incrementally.

Build Real-Time Communication Pipelines

Cloudflare’s real-time updates and technical transparency during and after the incident were praised — a blueprint for effective stakeholder trust-building.

Cloudflare's Post-Outage Improvements

• Introduced dynamic CPU pinning to isolate routing logic.

• Developed pre-deployment impact simulators for firewall + BGP changes.

• Reorganized change deployment workflow into wave-based rollouts with auto-abort triggers.

• Updated runbook dependency maps to include hardware-level failover details.

Career Cracker Insight

Whether it’s DNS, BGP, or config deployment — incident response is where leaders are made. You don't have to know everything, but you need to bring calm, structure, and action to chaos.

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• Lead bridge calls under pressure.

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• Perform root cause analysis and document RCAs like top tech firms.

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