Internet Gateway Demo

In this tutorial, you’ll convert a private subnet into a public subnet by attaching an Internet Gateway and updating the route table. After completing these steps, any EC2 instance launched in your public subnet will have Internet access.

Overview

Prerequisites

• An AWS account with permissions to manage VPCs and EC2.
• A generated SSH key pair (for example, aws-demo.pem).

1. Create a VPC and Public Subnet

1. In the AWS Console, go to VPC > Your VPCs and click Create VPC.
2. Set the IPv4 CIDR block to 10.0.0.0/16. Optionally add an IPv6 block.
3. Click Create VPC.

4. Navigate to Subnets > Create subnet:
   • Name tag: public-subnet
   • VPC: your newly created VPC
   • IPv4 CIDR block: 10.0.1.0/24
5. Click Create subnet.

2. Launch an EC2 Instance in the Public Subnet

1. Open EC2 Console > Instances > Launch instances.
2. For Name, enter my-public-server.
3. Choose Amazon Linux 2023 under Application and OS Images (AMI).

4. Select the t2.micro instance type (free tier).
5. Under Key pair, choose aws-demo.pem.
6. Expand Network settings > Edit and configure:
   • VPC: your new VPC
   • Subnet: public-subnet
   • Auto-assign public IP: Enable

7. Under Security group, allow SSH (port 22) from 0.0.0.0/0. Optionally add ICMP for ping.

8. Click Launch instance and wait for it to switch to running.

3. Verify Default Connectivity (Should Fail)

After your instance is running, copy its public IP (example: 54.159.89.36) and test connectivity:

ping 54.159.89.36
ssh -i aws-demo.pem [email protected]
# Connection hangs.

By default, there’s no Internet route, so the instance remains unreachable despite having a public IP.

4. Create and Attach an Internet Gateway

1. In the VPC Console, select Internet Gateways and click Create internet gateway.
   • Name tag: my-internet-gateway
2. Click Create internet gateway.
3. Select the newly created gateway, choose Actions > Attach to VPC, and select your VPC.

Pinging still fails because the route table isn’t updated yet.

5. Configure the Route Table for Internet Access

1. Go to VPC > Route Tables and click Create route table.
   • Name tag: public-route-table
   • VPC: your demo VPC
2. Click Create route table.
3. Select the new route table, open Subnet associations, click Edit subnet associations, check public-subnet, and save.

4. In the Routes tab, click Edit routes > Add route:
   • Destination: 0.0.0.0/0
   • Target: my-internet-gateway
5. Save the route.

6. Test Internet Connectivity (Should Succeed)

Now retry ping and SSH using the public IP:

ping 54.159.89.36
ssh -i aws-demo.pem [email protected]
# Welcome to your public EC2 instance!

Congratulations! Your public-subnet is now internet-enabled, and any EC2 instances launched into it can be accessed from the Internet.

Additional Resources

• AWS VPC User Guide
• AWS EC2 User Guide