Work queue saturated slow downstream
An async image-processing service uses a bounded in-memory work queue (capacity 1000) feeding a fixed pool of workers. At 17:00 the queue saturates at 1000/1000 and producers start getting rejected (HTTP 429 'queue full'); end-to-end latency for accepted jobs balloons. Worker CPU is only ~30% and there are free CPU cores. A thread/goroutine dump shows most workers blocked waiting on a downstream thumbnail-storage write that got slow after a storage-tier change at 16:50. Ingest rate is flat — no spike. Triage and mitigate.
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 35 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.