Most multi-cloud failover plans look convincing on a diagram. Traffic enters at the top, a box fails, arrows bend, traffic lands in the second cloud. The diagram is not wrong exactly — it is just drawn at the layer where failover is easy. Compute can be recreated from images and infrastructure code in minutes. What actually decides whether a failover works is everything underneath and around that compute: routes that were never built in the second cloud, data that is further behind than anyone assumed, identities that only exist on one side, and a cutover procedure the team has only ever read.

Failover fails at the seams between clouds, because the seams are the parts nobody owns end to end and nobody tests under load. Designing for that reality means treating recovery as a network and state problem first, and an application problem second.

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