VPC Peering & Transit

VPC Peering & Transit

In modern cloud architectures, connecting multiple Virtual Private Clouds (VPCs) is a common requirement—especially in multi-account or multi-region environments. AWS offers two powerful mechanisms for this: VPC Peering and Transit Gateway. Both enable VPC-to-VPC communication, but they serve different purposes and scale differently. Let's explore each in detail.

🔗 What Is VPC Peering?

VPC Peering is a networking connection between two VPCs that enables them to route traffic between each other using private IP addresses. It works similarly to a direct point-to-point link and does not require a gateway, VPN, or internet connection.

Key Features:

• Low-latency and high-bandwidth connectivity
• No single point of failure
• Works across regions (inter-region peering)

Example: Creating a VPC Peering Connection via AWS CLI

aws ec2 create-vpc-peering-connection \
  --vpc-id vpc-11111111 \
  --peer-vpc-id vpc-22222222 \
  --peer-region us-west-2

📍 Limitations of VPC Peering

• Peering connections are non-transitive (VPC A ↔ VPC B, but not A ↔ B ↔ C)
• Route tables must be manually updated for each VPC
• Complexity increases with more VPCs (full mesh)

🌐 What Is a Transit Gateway?

A Transit Gateway is a hub-and-spoke networking model that simplifies connecting multiple VPCs and on-premises networks through a central gateway. It allows thousands of VPCs to be connected without the full mesh configuration required by VPC Peering.

Key Features:

• Highly scalable — supports thousands of attachments
• Supports transitive routing
• Centralized management of routing

Example: Creating a Transit Gateway via AWS CLI

aws ec2 create-transit-gateway \
  --description "My Transit Gateway" \
  --options AmazonSideAsn=64512

Attaching a VPC to Transit Gateway:

aws ec2 create-transit-gateway-vpc-attachment \
  --transit-gateway-id tgw-0abc12345def67890 \
  --vpc-id vpc-11111111 \
  --subnet-ids subnet-aaa111bb subnet-bbb222cc

🔄 VPC Peering vs Transit Gateway

🏗️ When to Use VPC Peering

• You need to connect just a few VPCs
• Minimal routing complexity
• You prefer a lightweight and cost-effective solution

🛡️ When to Use Transit Gateway

• You’re building large, multi-account architectures
• You need centralized routing and security control
• You plan to scale to many VPCs or connect on-premises networks

💡 Best Practices

• Use VPC Peering for simple, isolated workloads
• Choose Transit Gateway for enterprise-grade scalability
• Always plan IP address ranges to avoid overlaps
• Tag your resources for easy identification and maintenance

🚀 Conclusion

Choosing between VPC Peering & Transit Gateway depends on your network scale, security model, and management preferences. While peering is excellent for small networks, Transit Gateway becomes a necessity in complex cloud architectures. A well-planned hybrid of both can also work based on organizational needs.