Calculating the SLA of a system behind a CDN

Cache

The content delivery network (CDN) is comprised of multiple caches spread across the globe in what’s called the “edge locations”. Let’s first examine one single cache.

  • Cache miss: when there’s no cached response available and the request should go all the way to the origin (our service) and probably be cached
  • Hit ratio = (Cache hit) / (Cache hit + Cache miss) * 100
  • Best case scenario: cache Availability

CDN

Content delivery network acts as a load balancer in front of multiple caches spread across the world. However, if all these caches reuse the same origin, it can introduce a single point of failure (SOP):

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Alex Ewerlöf

Alex Ewerlöf

Sr. Staff Engineer, Knowledge Worker, MSc Systems Engineering, Tech Lead, Web Developer