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Comment by manmal | Hacker News Reader

Though, using a specialized language like Erlang can make it possible to run WhatsApp on only 50 engineers (in 2015). I agree with the OP that choosing a stack like Rails can kill your Pokemon Go related MVP pretty quickly (I'm a huge Rails fan myself, but would definitely use Node.js for something like that).

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> make it possible to run WhatsApp on only 50 engineers

Frankly, I'm sure Erlang is great, but with 50 full time skilled engineers I'm pretty sure you could run WhatsApp on almost anything.

The largest explosion in their user base came when I think they were at something like ~11 engineers, and from what I've heard the largest additions to their engineering team came on the frontend side, not the backend.

Ask Twitter team; they may have a different story.

I'd probably do the first gen core chat in Node, and write everything else to leverage a cloud provider's infrastructure of choice.... Google, Azure and AWS all offer similar services which include bigtable, blob/file storage, some hosted SQL variant, document search engine, and some form of queuing service.

The hard part is routing messages, and looking at some of the messages, seems to be location based chats... probably could use geohashing for sending messages to channels, the hash level you are at, plus the surrounding 8 hashes.

Breaking up the server instance that a given chat connects to based on location hash would probably work out well enough. I'm not specifically familiar enough with the app... But it seems to me that channel growth and routing are the harder things in this at the scale of millions of users.

Depending on what kind of app the Rails stack is operating...it would follow the same exact pattern as Chat vs Photo Sharing in nodeJS as in the article. A Rails app running a JSON API server would do pretty well, and basically has the same boilerplate as the node hackathon thingy built in, plus a few extra gems.

Except it will collapse under it's own weight too quickly.... Rails is a pretty bad core for a chat engine.

Except that it's an order of magnitude slower than some other tech.

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