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The frontend needs to keep open thousands of persistent connections; 99.9% of which will time out with receiving a single message.

Practically speaking the number of frontend servers is related to the number of active listening clients and not messages.

Only 60 messages per second does seem very small from a business perspective however.

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If you take the frontend servers out of the equation it's still 52 servers for 60 messages per second.

My guess: the 60 messages per second is an average. Monday morning in the US timezones might see several multiples of that. Weekends could be a lot lower.

It's definitely very bursty. On weekends and holidays things are much more quiet. During peak load we'll be in the hundreds/sec. Also keep in mind that chat messages don't actually make up the majority of the traffic we serve; it's presence information (away, idle, available), people connecting/disconnecting, etc. (I'm one of the HipChat co-founders.)

And? The article makes no mention of what each server is responsible for, how much redundancy is built in (this is AWS where nodes die on a whim), whether all of these servers are used for production or if there is a spread across dev and staging environments, etc.

When all of these factors are considered, 52 servers isn't a huge number.

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