What is the purpose of having an internet gateway within a VPC?

An internet gateway is a service that allows for internet traffic to enter into a VPC. Otherwise, a VPC is completely segmented off and then the only way to get to it is potentially through a VPN connection rather than through internet connection. An internet gateway is a logical connection between an AWS VPC and the internet. It supports IPv4 and IPv6 traffic. It does not cause availability risks or bandwidth constraints on your network traffic1. An internet gateway enables resources in your public subnets (such as EC2 instances) to connect to the internet if the resource has a public IPv4 address or an IPv6 address. Similarly, resources on the internet can initiate a connection to resources in your subnet using the public IPv4 address or IPv6 address2. An internet gateway also provides a target in your VPC route tables for internet-routable traffic. For communication using IPv4, the internet gateway also performs network address translation (NAT). For communication using IPv6, NAT is not needed because IPv6 addresses are public2. To enable access to or from the internet for instances in a subnet in a VPC using an internet gateway, you must create an internet gateway and attach it to your VPC, add a route to your subnet’s route table that directs internet-bound traffic to the internet gateway, ensure thatinstances in your subnet have a public IPv4 address or an IPv6 address, and ensure that your network access control lists and security group rules allow the desired internet traffic to flow to and from your instance2. References: Connect to the internet using an internet gateway, AWS Internet Gateway and VPC Routing