TL;DR

Active-active means two or more locations serve live traffic at the same time, with the application running in each and its data replicated across them, so no location sits idle waiting for a failover. You build it in five layers, and data is the hardest:

Global routing: one endpoint sends each request to the nearest healthy location and stops sending traffic to a location that fails health checks.

Compute in every location: the same workload definition, image, and config run everywhere, and each location can absorb the others’ traffic.

Replicated data: a multi-writer database, a single writer with fast promotion, or a cell design keeps state available in more than one location.

Automatic failover: health signals remove a failed location from routing, in-flight requests drain, and clients retry safely, with no human in the loop.

Regular testing: game days, evacuation drills, and chaos experiments prove on a schedule that the first four layers work.

Control Plane runs the routing, multi-location…