Observability dashboard serving

Design the query/serving backend for an observability dashboarding product. A popular incident dashboard has 40 panels, each running a metrics query, and during an outage 500 engineers all load it at once, hammering the metrics backend with 20,000 near-identical queries in seconds. Dashboards auto-refresh every 30s. The metrics backend is the bottleneck and starts to brown out. Design the serving layer so dashboards stay fast and the backend survives the thundering herd.