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Code RoomFanout amplifies downstream load
HardPrep Room Coding #2673

Fanout amplifies downstream load

On-callDistributed systemsCode quality & reviewSenior–Staff~30 min

A push notification drives a 5x surge to your mobile home-screen API. Your home-screen service autoscales fine and stays healthy, but a shared downstream `user-profile` service — which it calls 8 times per home-screen request to hydrate widgets — saturates: profile p99 explodes, its DB hits connection limits, and home-screen requests start failing on the profile dependency. Profile is used by many teams and can't scale instantly. Dashboards show home-screen traffic up 5x but profile traffic up ~40x. How do you triage and mitigate without taking down profile for everyone?

What a strong answer looks like

Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.

0:00 of about 30 min
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