Attach Other Workload VPCs to Transit Gateway

In this section, you attach a workload VPC to your transit gateway and associate it with the workload oriented transit gateway route table.

Repeat the following steps for each workload VPC that you need to associate with your transit gateway.

1. Attach workload VPC to your transit gateway

First, access the AWS account in which the workload VPC of interest resides and create an attachment:

  1. As a Cloud Administrator, use your personal user to log into AWS SSO.
  2. Select the AWS account that contains a VPC that you need to attach to your transit gateway.
  3. Select Management console associated with the AWSAdministratorAccess role.
  4. Select the appropriate AWS region.
  5. Navigate to VPC
  6. Select Transit Gateway Attachments in the left navigation panel
  7. Select Create Transit Gateway Attachment
  8. Fill out the resource share form details. Some suggested fields are below:
Field Recommendation
Transit Gateway ID Select your transit gateway
Attachment type VPC
Attachment tag name Use the name of the VPC
DNS support checked
IP v6 support only check if you are using IP v6 - otherwise, leave unchecked
VPC ID Choose the VPC that you want to attach
Subnet IDs Select all of the subnets with which you want to associate with the transit gateway
  1. Select Create attachment

2. Accept transit gateway attachment request

Next, access the network-prod AWS account to accept the attachment request:

  1. As a Cloud Administrator, use your personal user to log into AWS SSO.
  2. Select the network-prod AWS account
  3. Select Management console associated with the AWSAdministratorAccess role.
  4. Select the appropriate AWS region.
  5. Navigate to VPC
  6. Select Transit Gateway Attachments in the left navigation panel

Within the table, you will see the list of your new pending acceptance transit gateway attachments.

  1. Select the checkbox next to each row where the status is pending acceptance
  2. Select Actions and select Accept
  3. A prompt will pop up. Select Accept to confirm acceptance of the attachment

3. Associate route table with VPC attachment

  1. Select the infra-workloads-vpcs route table
  2. Once the state of the route table transitions to available, select the Associations tab. You might have to refresh the page to see the state change.
  3. Select Create association
  4. Select the attachment to associate:
Field Recommendation
Choose attachment to associate Choose the transit gateway attachment id for the VPC attachment of interest
  1. Select Create association

4. Create propagation in network services route table

In order to allow traffic from your site-to-site VPN connection to be routed to the workload VPC, you will need to add a propagation for the VPC attachment to the network services route table.

  1. Select the infra-network-services route table
  2. Select the Propagations tab
  3. Select Create propagation
  4. Select the attachment to propagate
Field Recommendation
Choose attachment to propagate Select the transit gateway attachment id for the workload VPC attachment of interest
  1. Select Create propagation

5. Confirm propagation of routing information

  1. Select the Routes tab.
  2. You should see the CIDR range of the workload VPC of interest listed in the set of routes.

6. Update VPC route table

In this step, you’ll update the route table for each of the subnets in the workload VPC to add an entry to route traffic destined to your on-premises network to the transit gateway.

  1. Select Route Tables
  2. For each of the private subnets, modify the route table:
  3. Select route table entry in the list
  4. Select the Routes tab
  5. Select Edit routes
  6. Add a new route:
Field Recommendation
Destination Specify the CIDR range of your on-premises network
Target Select your transit gateway. For example, infra-main

Routing internet bound traffic to on-premises: If you choose to route all internet bound traffic back through your on-premises network, you can add another route for 0.0.0.0/0 in your route tables. You can use this approach as a temporary measure to direct all internet bound traffic through your existing on-premises network security services. Once you establish those services in your AWS environment, you can update the routing configuration as appropriate.