Connectivity (Joining Two Private Networks)

The board about joining two islands: what VPC & Subnets fenced off and Security Groups vs Network ACLs locked, now needing a door to another island just like it, right before Load Balancing & DNS (the operator's half) gives each island a name to be found by. This lesson is the five ways to build that door, and the one way to avoid building it at all.

Before you start. A VPC is an island: a private network with its own range of addresses that nothing outside it can see or reach on its own, the thing VPC & Subnets carved out of the ocean. You also need one fact about its fence: a rule that lets traffic in says nothing about whether traffic can reach the fence in the first place, which is what Security Groups vs Network ACLs drew the line on.