Three choices solve different problems
Direct VPC peering gives two VPCs a private route to each other without requiring traffic to pass through a third VPC. For a small number of carefully chosen relationships, it can be straightforward and avoids a shared transit hub. It is not transitive. If a team thinks its peering topology forms a general network graph through which packets can pass by hopping across peers, the design is already flawed.
A transit gateway attaches many VPCs and provides configurable route tables for traffic between them. A regional hub can simplify connectivity inside one region, and peerings between transit gateways can connect supported regions. On AWS, inter-region transit gateway peering needs explicit static routes. I would not assume one hub can simply forward through several other hub peerings or that route propagation between those peerings behaves like a global routing fabric. If a flow crosses regions, draw that exact supported path.
Private service endpoints such as PrivateLink solve a narrower problem. A consumer reaches a specifically published service through an endpoint instead of receiving full network routing to the provider's whole address space. This can be useful between organizational boundaries or where two VPCs use overlapping CIDRs. It does not provide general bidirectional VPC connectivity, and service support, cross-region capability and fees must be confirmed. For most teams, reduced network exposure is worth the extra configuration.
Regional independence must be designed, not named
Suppose a central hub in region A carries every control-plane request for all four regions. Region B still has working compute and databases, but the hub in A loses an attachment. B's services could fail even though no resource in B is broken. Calling the deployment multi-region would hide a shared failure domain.
I would group traffic into classes before choosing links. Local request serving should use regional dependencies whenever possible. Cross-region replication and recovery control traffic should travel on deliberate, measured paths. A small set of remote administrative APIs may use authenticated private endpoints. Data pipelines moving bulk bytes can use different capacity reservations from synchronous user-facing APIs. Separate route tables and security policies for these classes, and validate that production cannot accidentally route through development attachments.
That separation also makes failure tests meaningful. Remove the inter-region peer between A and B in staging. Which requests still complete locally? Which data replication stream pauses? Which asynchronous queue accumulates work? What can restart when connectivity returns? A network cut should not silently turn into a business-level permission to double-charge or discard work.
The bill and the traffic graph matter
The cheapest-looking topology on a slide may cost more in practice. Transit gateways and private endpoints can charge for attachments, endpoint-hours or processed bytes. Inter-region transfer has separate cost considerations. The precise numbers depend on provider, region and product, so I would use measured traffic matrices rather than inventing a universal price comparison.
For example, if a service makes forty remote API calls per user operation, moving those packets over a private backbone might change reliability or egress charges, but it will not remove physical round-trip latency. That calls for application redesign, which the final lesson in this series will address. Keeping networking and application communication costs separate prevents a more expensive private link from becoming a false performance fix.
I would build a matrix listing who initiates each connection, destination service, bytes transferred per day, latency budget, authentication, data classification and whether the flow may be unavailable during a region isolation event. This document is more useful than a picture with twelve fully connected boxes. It leads naturally to service endpoints for narrow relationships and regional transit hubs where many local workloads genuinely need routed connectivity.
The release gate would check actual subnet and hub route tables, DNS resolution, network policies, endpoint access policies and route-diff review. We would test attachment failure, wrong route propagation, overlapping address allocation, one-region isolation and rollback. Regional independence means those tests produce bounded effects. A topology diagram alone cannot prove it.
