Introduction.
In modern cloud architectures, organizations often use multiple Virtual Private Clouds (VPCs) to isolate environments, manage workloads, or separate accounts by business units. As the number of VPCs grows, the need for reliable, scalable, and maintainable inter-VPC communication becomes essential.
While AWS VPC Peering enables direct communication between two VPCs, it doesn’t scale well for complex architectures due to its point-to-point nature and lack of transitive routing.
This is where AWS Transit Gateway (TGW) becomes a powerful alternative.
AWS Transit Gateway acts as a central hub that simplifies and scales VPC connectivity. Instead of creating and managing numerous peering relationships, you connect each VPC once to the TGW.
The TGW then manages routing and connectivity between all attached VPCs or even on-premises networks through VPN or Direct Connect. This design dramatically reduces the complexity and operational overhead involved in managing network topologies.
A Peer VPC architecture using Transit Gateway involves attaching multiple VPCs to a single TGW and configuring routing to enable communication between them. Each VPC uses a TGW attachment, which is essentially a link that connects a VPC to the TGW. Traffic between VPCs flows through the TGW, which uses route tables to determine how traffic is forwarded.
Key components of this architecture include the VPCs themselves, the Transit Gateway, Transit Gateway route tables, VPC route tables, and optional elements like security groups, network ACLs, and shared services VPCs. TGW route tables can be customized to control which VPCs can communicate with each other, making it flexible for various network segmentation requirements.
Security is a critical aspect when setting up inter-VPC communication. Each VPC’s security groups and network ACLs must explicitly allow traffic from the CIDR ranges of the other VPCs involved. Similarly, VPC route tables must have entries that direct traffic for peer VPC CIDRs to the Transit Gateway.
If the VPCs are in different AWS accounts, AWS Resource Access Manager (RAM) can be used to share the TGW. For multi-region setups, inter-region TGW peering can be configured, enabling global VPC communication.
In summary, using AWS Transit Gateway to peer VPCs provides a highly scalable, centralized, and simplified way to manage network connectivity in large AWS environments. It replaces the complexity of many-to-many peering with a hub-and-spoke model that supports granular routing control, high availability, and performance.
This architecture is ideal for enterprises with multiple accounts, microservices distributed across VPCs, or hybrid networks that include on-premises systems. The Transit Gateway model not only simplifies connectivity but also lays a solid foundation for secure and scalable cloud networking.
Step 1: Create VPCs
You’ll need at least two VPCs in the same or different AWS accounts/regions:
- VPC-A
- VPC-B
Each should have:
- CIDR block (no overlapping)
- At least one subnet
- Internet Gateway (optional)
- Route tables
Step 2: Create a Transit Gateway (TGW)
- Go to VPC Dashboard → Transit Gateways.
- Click Create Transit Gateway.
- Provide:
- Name tag
- Amazon ASN (default or custom)
- Enable/disable DNS support (enable if VPC DNS resolution is needed)
- Click Create Transit Gateway.
Step 3: Attach VPCs to the Transit Gateway
Repeat the following for each VPC:
- Go to Transit Gateway Attachments → Create Transit Gateway Attachment.
- Select:
- Transit Gateway
- VPC to attach
- Select the subnet(s) in the VPC.
- Click Create attachment.
- Wait for the status to become “Available”.
Step 4: Update Route Tables in Each VPC
To enable communication between VPCs via TGW:
- Go to Route Tables in each VPC.
- Add a route:
- Destination: CIDR of the other VPC (e.g., VPC-B’s CIDR in VPC-A)
- Target: The Transit Gateway
Repeat this in both directions:
- VPC-A ➜ VPC-B via TGW
- VPC-B ➜ VPC-A via TGW
Step 5: Update Transit Gateway Route Table
Transit Gateways have their own route tables.
- Go to Transit Gateway Route Tables.
- Select the TGW Route Table associated with your attachments.
- Add routes:
- Destination: VPC-B’s CIDR → Target: VPC-B Attachment
- Destination: VPC-A’s CIDR → Target: VPC-A Attachment
(If using the same TGW route table for all VPCs, this is usually automatic.)
Step 6: Verify Communication
- Launch EC2 instances in each VPC.
- Ensure security groups and network ACLs allow traffic.
- Ping from one instance to another (e.g., via private IP).
Conclusion.
Implementing VPC peering using AWS Transit Gateway offers a scalable, centralized, and efficient approach to interconnecting multiple VPCs across accounts and regions. Unlike traditional VPC peering, which can become complex and unmanageable as the number of connections increases, Transit Gateway simplifies the architecture by acting as a single hub for all network communication.
By leveraging Transit Gateway, organizations can enforce consistent routing policies, reduce management overhead, and improve network visibility. The use of TGW route tables and attachments provides fine-grained control over traffic flow, allowing for secure segmentation and communication between environments such as production, development, and shared services.
This architecture is especially beneficial in multi-account, multi-region, or hybrid cloud setups, supporting not only VPC-to-VPC communication but also integration with on-premises networks via VPN or Direct Connect.
In conclusion, Transit Gateway is a powerful solution for enterprises looking to future-proof their AWS networking strategy, enabling seamless connectivity, enhanced security, and operational simplicity as cloud environments continue to grow and evolve.
