BGP prefix withdrawal
At 02:14 your edge starts dropping ~30% of inbound traffic for users in Europe; the rest of the world is fine. Synthetic probes from EU vantage points time out before reaching your edge IPs, while probes from US/APAC succeed. Your edge servers show a sharp drop in connections from EU ASNs but are otherwise healthy. A network engineer pushed a routing/peering change ~15 minutes before the incident: a BGP prefix announcement was adjusted to shift EU traffic onto a new transit provider. Traceroutes from affected EU networks die a few hops in, in the new transit's network. Walk through triage, mitigation, and prevention.
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.