Large request hangs
After migrating a service into a new VPC behind a VPN/overlay tunnel, small requests work perfectly but any request with a large body (file uploads, big JSON payloads) hangs and eventually times out. curl with small payloads returns instantly; the same endpoint with a 20KB body never completes. Packet captures show the large request's first few packets arrive, then silence — the connection stalls mid-transfer and no RST is seen. Pings of normal size succeed; `ping -s 1472 -M do` (don't-fragment) to the peer fails with no reply. The overlay/VPN was introduced in the migration. Diagnose and fix.
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.