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/AWS Transit Gateway isolated routing with Shared Services/

AWS Transit Gateway isolated routing with Shared Services



We are working with a client that has the following setup: 1 TGW that has 5 VPC attachments

  • non-prod a attachment
  • non-prod b attachment
  • prod-a attachment
  • prod-b attachment
  • shared-services attachment

Requirements: The client would like to allow only for inter-communication of both the non-prod VPCs, as well as the prod VPCs. Additionally, the client would like for shared-services to be able to reach any of the VPCs.

My initial approach and the problem: Initially, my thought was to create 3 isolated routing domains, which were represented by 3 separate TGW route tables. I was unable to achieve this because there is a limitation of only being able to associate 1 attachment with 1 TGW route table. If we were able to make more than one attachment for the same VPC, we could get around this issue, but unfortunately that is not possible.

Looking for recommendations on the best way to address the above requirements.

The only other option I can think of to accomplish these requirements is to use 1 TGW route table, associate all of the attachments with it, and then ultimately use NACLs in the individual VPCs to restrict traffic. To me, this seems like a pain to maintain, so I wanted to see if there are any other ways to address this problem.

More Information on what I've already tried

My initial idea was to have 3 TGW route tables (one for each "routing domain"):

  • non-prod (associated with the non-prod-* attachments)
  • prod (associated with the prod-* attachments)
  • shared (associated with all attachments)

The problem with this approach is the shared TGW route table because as I mentioned above, you can't associate an attachment with more than one route table. In essence this is a "flat" routing architecture rather than isolated and directly contradicts with what I'm trying to do causing this problem.

Thanks in advance!

1 Answers
Accepted Answer

I think this gets what you need?

NPA and NPB attachment Route Table:

NPA CIDR --> NPA attachment
NPB CIDR --> NPB attachment
SS CIDR --> SS attachment

Traffic arriving from NPA or NPB attachment can go SS, NPA, or NPB

PRA and PRB attachment route table

PRA CIDR --> PRA attachment
PRB CIDR --> PRB attachment
SS CIDR --> SS attachment

Traffic arriving from PRA or PRB attachment can go SS, PRA or PRB

SS Attachment route table

NPA CIDR --> NPA attachment
NPB CIDR --> NPB attachment
PRA CIDR --> PRA attachment
PRB CIDR --> PRB attachment

Traffic from SS attachment can go NPA, NPB, PRA, or PRB

answered 2 years ago

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