How to filter subnets according to a VPC in CloudFormation's parameters section?-CodePudding

I want to list out the subnets only from specific VPC in my cloudformation parameters section

VPC:
    Description: VPC Id
    Type: AWS::EC2::VPC::Id 

Subnets:
    Description: Select Subnets (Minimum 2)
    Type: List<AWS::EC2::Subnet::Id>

The above displays all subnets (from other subnets also) but I want to show only subnets from selected VPC.

Is it possible? What is the workaround for the same?

CodePudding user response：

Is it possible?

No.

What is the workaround for the same?

There is none, unless you develop your own frotnend for deployment of templates.

CodePudding user response：

You can't list them that way, but you can prevent deployment if the chosen subnets are not in the VPC by using a CloudFormation rule:

{
  "Rules": {
    "IsSubnetInsideVPC": {
      "Assertions": [
        {
          "Assert": {
            "Fn::EachMemberEquals" : [
              {
                "Fn::ValueOfAll": [
                  "AWS::EC2::Subnet::Id",
                  "VpcId"
                ]
              },
              {
                "Ref": "VPC"
              }
            ]
          },
          "AssertDescription": "One or more subnets you selected are not in the VPC"
        }
      ]
    }
  }
}