AWS Cloudformation nested Functions (Split, Select, Join, Ref)

+1 vote

I am trying to do the following:

  1. Get the CIDR block set by the user in the Parameters
  2. Split the CIDR by "." to get the individual numbers
  3. Join CIDR[0], CIDR[1], "4.0/24"

I have come up with the following funciton:

"CidrBlock": {
                "Join": [
                    ".",
                    [
                        {
                            "Select": [
                                "0",
                                {
                                    "Split": [
                                        ".",
                                        {
                                            "Ref": "2CIDR"
                                        }
                                    ]
                                }
                            ]
                        },
                        {
                            "Select": [
                                "1",
                                {
                                    "Split": [
                                        ".",
                                        {
                                            "Ref": "2CIDR"
                                        }
                                    ]
                                }
                            ]
                        },
                        "16.0/24"
                    ]
                ]
            },

But this fails with the following error:

Value of property CidrBlock must be of type String

I cannot find any examples of what I am trying to do on the internet.

Anyone has any idea what's wrong with the above function? Or can anyone suggest an alternative way to build the CIDR of each subnet using the CIDR of the VPC?

Sep 11, 2018 in AWS by bug_seeker
• 15,310 points
584 views

2 answers to this question.

+2 votes

Maybe what's wrong is that "Join" is not a function. "Fn::Join" is.

answered Sep 11, 2018 by Priyaj
• 56,160 points
+2 votes
"Join" is not a function. "Fn::Join" is.
answered May 16 by Nalin Kant Gupta
Totally agree with you. @Nalin

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