580 notifications a second, 10 million sockets: size the live tier by connections

transcript

Your app sends about 580 in-app notifications a second. So you size your servers for 580 a second. Wrong number. Here's the one that matters.

Evening peak. About 15 percent of 50 million users are online. That's 7.5 million people. With about 1.33 devices each. Roughly 10 million open sockets.

But here's the catch. Even an idle socket talks. Heartbeats alone outnumber in-app notifications. More than 100 to 1.

Messages? About 580 a second. The small part. The real cost is holding 10 million sockets. Each one costs memory, all evening long. And when they drop together, how fast can they come back?

Lose one zone, and 3.3 million sockets reconnect together. So the gate isn't message speed. It's admission control. Let them back in steadily, and everyone's online again.

A live tier isn't sized by what it sends. It's sized by who's connected. And how fast they return.

Full breakdown in the lecture.