When new subnets are created within a custom VPC, can they communicate with each other by default?

When new subnets are created within a custom Virtual Private Cloud (VPC), they can communicate with each other by default. This is due to the fact that subnets within the same VPC share the same routing table, allowing traffic to be routed internally among those subnets without additional configuration.

The ability for subnets to communicate is fundamental to the way VPC networking is designed. Once you create a subnet in a VPC, AWS automatically sets up routing that enables instances within those subnets to send traffic to and receive traffic from each other. This applies to any subnets created within the same VPC, regardless of whether they are in the same availability zone or spread across multiple zones.

This characteristic supports the design of scalable and flexible architecture, where different components of an application can easily interact within the same network environment. When additional security controls or isolation are needed, it is the use of Network Access Control Lists (NACLs) or security groups that determine the traffic flow rather than the inherent capability of subnets to communicate.