Phil Karlton once said, “There are only two hard things in Computer Science: cache invalidation and naming things.” This article is about the harder of these two: cache invalidation. It’s directed at readers who already work with Varnish Cache. To learn more about it, you’ll find background information in “Speed Up Your Mobile Website With Varnish.”
10 microseconds (or 250 milliseconds): That’s the difference between delivering a cache hit and delivering a cache miss.
Cache Invalidation Strategies With Varnish Cache
Imagine that your biggest client calls because they are having trouble retrieving their email. Or they want to know what their best-selling item is right now. Or their most popular blog post. Perhaps their website has suddenly gone down. You can hardly reply, “No problem, I’ll get back to you in 24 to 48 hours.”
And yet DNS gets away with it! If you need to move a website or change the way a domain’s email is handled, you’ll be faced with a vague 24 to 48-hour delay.
Introduction to DNS: Explaining The Dreaded DNS Delay