What is AWS internet gateway?

The internet gateway is provided at no additional cost with your AWS account. It can be associated with any of your VPCs and is not restricted to a specific availability zone. Since the internet gateway is a virtual component, it doesn’t have a physical connection to the VPC, but instead provides a virtual link between the VPC and the internet.

Internet gateway

In the diagram below, an internet gateway is shown within the AWS Cloud architecture. Every VPC has a route table by default, which facilitates communication between resources inside the VPC. The first route entry handles internal communication within the VPC. However, to enable internet traffic, you need to add a specific route that directs the traffic to the internet gateway, often referred to as “igw," as seen in the second entry of the route table.

Why is the internet gateway important?

Here are some key benefits of using an internet gateway (IGW) in your network:

• Facilitates internet communication: The IGW is essential for enabling outbound and inbound internet traffic for public-facing resources.

• Cost-efficient: AWS offers the internet gateway as a free service without additional charges for bandwidth or scaling.

• Supports high availability: Since it’s a managed AWS service, the internet gateway doesn’t require manual scaling and is designed for availability across multiple availability zones.

How does an internet gateway work?

The AWS internet gateway is not a physical device but a logical connection allowing bidirectional traffic between the internet and instances located in a public subnet of your VPC. When a public subnet has an associated internet gateway, EC2 instances with public IP addresses can communicate freely with the outside world.

If your instances are within a private subnet, they cannot directly access the internet through the internet gateway. For such cases, a NAT gateway is required to allow outbound-only connections while blocking inbound internet traffic, ensuring additional security for sensitive data.

Components and role in a VPC

• Route table integration: To route traffic from your VPC to the internet, a route must be added to the VPC route table. This route directs traffic destined for the internet (typically 0.0.0.0/0 for IPv4) through the internet gateway.

• Security groups and network ACLs: Both security groups and network access control lists (NACLs) play an essential role in controlling the traffic flowing to and from your VPC instances. Ensure proper rules are defined to allow legitimate traffic.

How to configure an internet gateway in AWS

Follow these steps to configure an internet gateway for your VPC:

1. Create an internet gateway:

   1. Open the AWS Management Console and navigate to VPC > Internet Gateways.

   2. Click on "Create internet gateway" and give it a name for easy identification.

2. Attach the internet gateway to a VPC:

   1. Once created, attach the IGW to your desired VPC. An internet gateway can only be attached to one VPC at a time.

3. Modify the route table:

   1. Go to the "Route Tables" section of your VPC.

   2. Select the route table associated with your public subnet.

   3. Add a route with the destination 0.0.0.0/0 (for IPv4) and ::/0 (for IPv6) with the target set to the newly created internet gateway.

4. Update security groups and network ACLs:

   1. Ensure that your security groups and NACLs allow traffic from the internet. Modify inbound and outbound rules to permit HTTP, HTTPS, or other relevant protocols.

Note: Always configure your route tables, security groups, and network ACLs correctly to secure your environment while maintaining necessary access.

Advantages of the AWS internet gateway

1. Scalability: The internet gateway automatically scales to handle your VPC’s internet traffic without manual intervention.

2. Cost efficiency: As a free service, there are no direct charges for using the internet gateway.

3. Availability: The IGW spans across multiple availability zones, ensuring reliable and redundant internet connectivity.

Common use cases for an internet gateway

1. Hosting public-facing applications: Applications like web servers hosted in EC2 instances require internet access to serve content to users. The IGW enables this connectivity.

2. Accessing AWS services via public IP: If assigned public IP addresses, resources in a VPC can access AWS services like S3 or DynamoDB through the internet gateway.

3. Outbound data transfer: Services that need to send logs, data, or metrics to external monitoring tools or third-party APIs rely on IGW for outbound communication.

Conclusion

The AWS internet gateway plays an important role in enabling internet communication for resources inside your VPC. Whether you’re hosting public-facing applications or routing traffic securely through a NAT gateway, the internet gateway ensures flexible, scalable, and reliable connectivity with the outside world. Without it, accessing the internet from a VPC would require additional resources such as VPN or AWS direct connect.