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While I agree we should not assume a cdn is necessary, as far as user traffic is concerned, not all seconds are created equal. Those pesky users have a habit of

While I agree we should not assume a cdn is necessary, as far as user traffic is concerned, not all seconds are created equal. Those pesky users have a habit of making requests at the same time, like they're in cahoots with one another. Whether it's because they're all in the same time zone and they just got home from work, or the clock struck midnight and your fire sale has begun, you don't provision for average qps, you provision for peak qps. This does not negate your argument, in fact for many use cases doing your own caching could be a better way to meet increased demand (certainly a cheaper way). CDN-related issues can be incredibly difficult to troubleshoot, too, especially without a support contract.

jerf 4y ago
By all means, if You Are Indeed (Some Reasonable Fraction Of) Google, then by all means, take that seriously. But I can tell you from personal experience I've been asked to produce a "CDN plan" for content access on the order of once a minute during peak hours, and which had no reasonable business case for distributing enough to matter. I am personally responsible for one system that does need CDN-like capability, because it does serve static files at a rate and a required reliability that a single server can't meet. (We don't use a "real" CDN because for our use case it would be absurdly expensive, but we're keeping an eye on the offerings out there.) So I do know they can exist. But even that system is, in 2022, on the lower end of what you would need such a thing for, and it is serving multi-gigabyte images out on a fairly routine basis to many tens of thousands of consumers (which are automated systems, not humans). That's what it takes to be on the "low end" of blowing out a normal static file server. 15 years ago these systems were a royal pain to maintain, at a much lower level of usage, and non-trivial effort was spent optimizing what they serve. Today, they mostly just hum away doing their job.

jerf 4y ago

By all means, if You Are Indeed (Some Reasonable Fraction Of) Google, then by all means, take that seriously. But I can tell you from personal experience I've been asked to produce a "CDN plan" for content access on the order of once a minute during peak hours, and which had no reasonable business case for distributing enough to matter. I am personally responsible for one system that does need CDN-like capability, because it does serve static files at a rate and a required reliability that a single server can't meet. (We don't use a "real" CDN because for our use case it would be absurdly expensive, but we're keeping an eye on the offerings out there.) So I do know they can exist. But even that system is, in 2022, on the lower end of what you would need such a thing for, and it is serving multi-gigabyte images out on a fairly routine basis to many tens of thousands of consumers (which are automated systems, not humans). That's what it takes to be on the "low end" of blowing out a normal static file server. 15 years ago these systems were a royal pain to maintain, at a much lower level of usage, and non-trivial effort was spent optimizing what they serve. Today, they mostly just hum away doing their job.