I have a list of subnets that I would want to iterate into my public and private route table. Here is an example of my function for my public RT:

// This will grab the public RT and associate all public subnets to the RT.
props.pubSubnetId.forEach((public_subnets) => {
  const publicRTAssoc = new ec2.CfnSubnetRouteTableAssociation(this, "publicRTAssoc", {
    routeTableId: props.pubRouteTableId,
    subnetId: public_subnets
  });
});

I see nothing wrong with my code but when I run cdk synth, I get this error:

Error: There is already a Construct with name 'publicRTAssoc' in CloudformationArchStack [CloudformationArchStack]

I believe the iteration is interfering with the id in my function. Would appreciate any help in solving this problem.

>Solution :

Your suspicions were correct. You just need to give each route table association construct a unique id:

// This will grab the public RT and associate all public subnets to the RT.
props.pubSubnetId.forEach((public_subnets) => {
  const publicRTAssoc = new ec2.CfnSubnetRouteTableAssociation(this, `publicRTAssoc_${public_subnets}`, {
    routeTableId: props.pubRouteTableId,
    subnetId: public_subnets
  });
});