Checkout calls five downstream services. Design backpressure so overload degrades instead of collapsing.

Every overloaded system dies the same way: queues turn load into latency, latency into timeouts, timeouts into retry storms. Tiered shedding, deadline propagation, and retry budgets are the design.

Grounded in researched DevOps, SRE and platform engineering interview loops, written to a senior-engineer editorial bar, and never padded to hit a word count.