What is an Egress-Only Internet Gateway (EIGW) used for in AWS?

An Egress-Only Internet Gateway (EIGW) is specifically designed to allow outbound internet access for resources within an Amazon Virtual Private Cloud (VPC) while preventing those resources from receiving inbound internet traffic. This is particularly important for use cases involving IPv6-enabled resources, where communication can be initiated from the VPC to the internet without compromising the security and integrity of the data and systems within the VPC.

Utilizing an EIGW, resources such as EC2 instances can connect to the internet to download updates or communicate with external services while remaining unreachable from the internet. This enhances security by preventing unsolicited traffic from reaching these resources, ensuring that only intentionally initiated outbound connections are allowed.

The other options do not correctly describe the primary function of an Egress-Only Internet Gateway. For example, it does not provide inbound internet access; rather, it specifically restricts this type of access. It also does not enable IPv4 address assignments, since that is inherently managed by the private addressing scheme of the VPC itself. Finally, it does not block all internet traffic but selectively allows outbound communication while maintaining a layer of security against incoming traffic.