Most multi-cloud architecture diagrams draw each cloud as a tidy box. Inside the boxes there are VPCs, subnets, managed services, and careful labels. Between the boxes there is usually a single line, sometimes labelled just "VPN" or "internet".

That line is where a surprising amount of production pain lives.

As soon as a workload in one cloud genuinely depends on data or services in another — a reporting job reading from a database that stayed behind, an application calling an AI endpoint hosted elsewhere, a failover that suddenly reroutes traffic across providers — the lines between the boxes stop being decoration. They become a network that somebody has to design, secure, document, and debug at 2 a.m.

This is a planning outline for treating inter-cloud connectivity as a designed layer in its own right, before the estate grows enough that retrofitting it becomes expensive.

1. Inventory the flows before choosing any technology

The most common mistake is starting with connection products.…