CDN Invalidation Storm Causes Origin Overload

Question

A misconfigured deployment invalidates most CDN cache objects at once, flooding the origin. What’s your triage and prevention plan?

Accepted Answer

A sudden, widespread CDN cache invalidation is a critical incident that requires immediate, structured triage to mitigate origin overload. My approach would prioritize minimizing impact to the origin while restoring service functionality and then implementing preventative measures. Immediately pause all non-essential or bulk invalidation requests. This is the first line of defense to stop the bleeding and prevent further flooding. Concurrently, I would identify the source of the misconfiguration and begin rollback or correction. Implement a throttling or queueing mechanism for any necessary, immediate invalidations. This ensures that the origin is not overwhelmed by a sudden burst of requests, allowing it to process them in a manageable flow. This might involve manual intervention or leveraging CDN features for granular control. Enable 'stale-while-revalidate' and 'serve-stale-on-error' settings where applicable. This allows the CDN to serve cached content to users even if it's slightly out of date while asynchronously fetching fresh content from the origin. This significantly reduces the immediate load on the origin during recovery. Temporarily scale up origin capacity or activate origin shield/tiering solutions. This provides a buffer to absorb the increased traffic that will inevitably occur as stale content is revalidated. Origin shield, in particular, can absorb many requests at the edge, further protecting the primary origin. Once the immediate crisis is averted, conduct a thorough post-mortem. This involves analyzing the root cause of the misconfiguration, identifying gaps in deployment validation and testing, and updating our operational procedures to prevent recurrence. The key to handling such an incident lies in swift, decisive action to mitigate the immediate impact and a robust post-incident analysis to ensure long-term resilience. Continuous monitoring and proactive testing of deployment processes are paramount for preventing future occurrences.

CDN Invalidation Storm Causes Origin Overload

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