Building a Public & Private Cloud Network in AWS: VPC Setup, EC2 Launch, and Cross-Instance Connectivity

Introduction

Amazon Web Services (AWS) offers robust networking capabilities through Virtual Private Cloud (VPC), allowing you to design secure, isolated network environments. In this guide, we’ll:

• Create a VPC with both public and private subnets

• Launch EC2 instances in each subnet

• Connect to instances using MobaXterm from a Windows machine

• Test cross-instance connectivity by pinging IP addresses

By the end, you’ll understand how public and private networks work together in AWS.

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Step-by-Step Guide

1. Create a VPC

1. Go to the AWS Management Console → VPC Service

2. Click Create VPC

   • Name: My-VPC

   • IPv4 CIDR block: 10.0.0.0/16

   • Tenancy: Default

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2. Create Public and Private Subnets

1. Public Subnet

   • Name: Public-Subnet

   • CIDR: 10.0.1.0/24

   • Availability Zone: ap-south-1a

   • Enable Auto-assign public IP: Yes

2. Private Subnet

   • Name: Private-Subnet

   • CIDR: 10.0.2.0/24

   • Availability Zone: ap-south-1a

   • Auto-assign public IP: No

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3. Create an Internet Gateway (IGW)

• Go to Internet Gateways → Create IGW → Attach it to My-VPC

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4. Create Route Tables

1. Public Route Table

   • Associate with Public Subnet

   • Add route: 0.0.0.0/0 → Internet Gateway

2. Private Route Table

   • Associate with Private Subnet

   • No internet route (for private network isolation)

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5. Launch EC2 Instances

1. Public Instance

   • AMI: Amazon Linux 2

   • Instance type: t2.micro

   • Subnet: Public-Subnet (auto-assign public IP)

   • Security Group: Allow SSH from your IP, Allow ICMP (ping)

2. Private Instance

   • Same AMI & type

   • Subnet: Private-Subnet (no public IP)

   • Security Group: Allow ICMP and SSH from the Public Instance’s private IP range

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6. Connect via MobaXterm (Windows)

1. Download & install MobaXterm on your Windows machine

2. Connect to Public Instance using .pem key

3. From the public instance, SSH into the private instance:

    ssh -i mykey.pem ec2-user@<Private-Instance-Private-IP>
   

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7. Test Connectivity Between Instances

1. From Public Instance:

    ping <Private-Instance-Private-IP>
   

2. From Private Instance:

    ping <Public-Instance-Private-IP>
   

If ICMP is allowed in both security groups, you should see successful replies.

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Architecture Diagram

Here’s a visual representation:

   +-------------------+              +-------------------+
   |   Public Subnet   |              |   Private Subnet  |
   |  EC2: Public Inst |              |  EC2: Private Inst|
   |   10.0.1.x        |              |   10.0.2.x        |
   +---------+---------+              +---------+---------+
             |                                   |
        Internet GW                          No Internet
             |
         Your PC (MobaXterm)

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Conclusion

By setting up a VPC with both public and private subnets, we achieve secure, segmented networking in AWS. The public subnet allows external access (via the Internet Gateway), while the private subnet ensures internal-only resources. Using MobaXterm simplifies remote access from Windows, and ping tests validate internal communication.

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Key Learnings

• Public subnets provide internet accessibility; private subnets keep workloads secure.

• Security groups and routing tables control traffic flow.

• MobaXterm is a powerful SSH client for Windows users.

• Internal networking in AWS can be tested using simple ping commands.

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