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Code RoomHTTP/2 stream head-of-line blocking
HardPrep Room Coding #2784

HTTP/2 stream head-of-line blocking

On-callNetworking & APIsSenior–Staff~40 min

Your mobile API moved all client traffic onto a single multiplexed HTTP/2 connection per client (over TLS/TCP) to cut handshakes. It works great on good networks. But users on lossy mobile networks now report that when ANY request stalls, ALL their in-flight requests stall together and then recover together — even small independent calls. Server-side everything is healthy and fast; the server's per-stream metrics show no slow handlers. Packet-capture from affected clients shows TCP retransmissions right before each multi-stream stall. How do you triage and what are the options?

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 40 min
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