Edge caching
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Updating the edge cache in the background while serving stale content can improve performance. Nginx has an undocumented side effect in this behavior, which can negate the performance gains when used in a high-load environment.
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Request coalescing prevents simultaneous requests from hitting the origin at the same time by allowing a single request to populate the cache, and then serving waiting requests from the cache. Nginx achieves that via proxy_cache_lock, which has an undocumented performance hit, causing requests to have up to 500ms slower response times.
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The guide focuses on optimising and debugging edge caching on the WordPress VIP platform. I share insights on enhancing performance for WordPress and Node.js applications, along with troubleshooting edge behaviour.