Bulkhead

1. The Incident

One API deployment handles checkout, search, and order history by sharing 200 threads and 100 database connections. A pool is a fixed set of workers or connections that requests temporarily use.

Marketing then sends 2 million emails linking to the order history page, increasing its traffic from 50 to 1,500 requests per second. Each order history request performs the service's most expensive query and takes about 500 ms.

The module's calculation gives work in progress = arrival rate x processing time, so this traffic requires 1,500 x 0.5 = 750 concurrent threads