What must be attached to a VPC to allow instances in that VPC to receive inbound traffic from the internet?

An Internet Gateway (IGW) is a horizontally scaled, redundant, and highly available VPC component that allows communication between instances in your VPC and the internet. It provides a target for internet-routable traffic in your VPC route tables and performs network address translation (NAT) for instances that have public IPv4 addresses. Without an IGW, instances in a VPC cannot directly send or receive traffic from the internet. A NAT gateway allows instances in a private subnet to connect to the internet or other AWS services but prevents the internet from initiating a connection with those instances. A VPC endpoint allows private connections to supported AWS services without traversing the internet. A VPN connection establishes a secure connection between your on-premises network and your VPC.