Select VPC created from cloudformation

Question

I am creating two EKS templates and one VPC template. In VPC template I have created 3 private and 3 public subnets which is working fine. So, I want one EKS should be in public and one EKS should be in private subnets. So how can do it via cloudformation.

Type: List<AWS::EC2::Subnet::Id>

This gives me list of subnets which is 6.

Ec2SubnetId: 
     !Select [0, !Ref SubnetIds]

This selects 1st subnet from all subnets. But I am not sure how to select 3 particular public or private subnet only in cloudformation.

asr9 asr9 · Accepted Answer · 2019-02-22T11:41:50

If I understand you want a list of private & public subnets your VPC stack created. You can export your public & private subnets from the VPC stack & use them in your EKS stacks.

Outputs:
  PublicSubnets:
    Description: Public Subnets
    Value: !Join [",", [!Ref PublicSubnet1, !Ref PublicSubnet2, !Ref PublicSubnet3]]
    Export:
      Name: PublicSubnets  
  PrivateSubnets:
    Description: Private Subnets
    Value: !Join [",", [!Ref PrivateSubnet1, !Ref PrivateSubnet2, !Ref PrivateSubnet3]]
    Export:
      Name: PrivateSubnets

I think you should now be able to refer them in your EKS stack as

Ec2SubnetId: 
 !Select [0, !ImportValue PrivateSubnets]

or maybe a Split function

Ec2SubnetId:
  !Select [0, !Split [",", !ImportValue PrivateSubnets]]

Let me know if that works.

Select VPC created from cloudformation

2 Answers