Auto selecting subnet parameter value

Question

I am using the following code of Parameters to select the latest AMI. It works as execpted.

"Parameters" : {
  "LatestAmiId" : { 
    "Type" : "AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>",
    "Default" : "/aws/service/ami-amazon-linux-latest/amzn-ami-hvm-x86_64-ebs"
}},

Is there a similar way to select the subnet of default security group? I do not want to mention the subnet (or security group) like this...

"SubnetId": "subnet-e8ecf09c, subnet-aa9dfc90, subnet-ce083188, subnet-718bd259",

Update:

I am using the following code and it fails with an error " Value of property SubnetId must be of type String"

{
"Parameters": {
  "LatestAmiId": {
    "Type": "AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>",     
    "Default": "/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-ebs"
},

  "myKeyPair" : {
    "Description" : "Amazon EC2 Key Pair",
    "Type" : "AWS::EC2::KeyPair::KeyName"
  },
  "mySubnetIDs" : {
    "Description" : "Subnet IDs",
    "Type" : "List<AWS::EC2::Subnet::Id>"
  },
     "Oksoftaccess":{  
         "Type":"AWS::SSM::Parameter::Value<String>",
         "Default":"myEC2TypeDev"
      },
      "Oksoftsecret":{  
         "Type":"String",
         "Default":"mysecret1"
      }
},

Prabhakar Reddy · Accepted Answer · 2018-12-23 09:55:12Z

1

As per this document, the “SubnetId” property in the “AWS::EC2::Instance” must be “String” type. However, the parameter type called “Subnet” is defined as “List” which is a list . EC2 instances can be run in the only one subnet (not multiple subnets).

Change the parameter type to “AWS::EC2::Subnet::Id” as below in your CF template and then try again:

    "mySubnetIDs": {
     ...
        "Type": "AWS::EC2::Subnet::Id"
     ...
    }

answered Dec 23, 2018 at 9:55

Prabhakar Reddy

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