CloudFormation Join in Tags

Question

I'm running a CloudFormation template that uses the following snippet to tag various resources (this is a ELB tag, but others also exhibit this problem) I would expect this to produce a name tag of stackName-asgElb but it actually produces names such as olive-asg-asgElb-16GSCPHUFSWEN .

The stack name in this case was named olive-asg so I was expecting olive-asg-asgElb , without the -16GSCPHUFSWEN on the end.

Does anybody know where the seemingly random string on the end comes from?

CF template snippet :

Tags: [
    {
        Key: "Name",
        Value: {
            "Fn::Join": [
                "-",
                [
                    {
                        Ref: "AWS::StackName"
                    },
                    "asgElb"
                ]
            ]
        }
    }
]

Answer 1

That's interesting, I just tried it and I'm not able to reproduce the same results that you're seeing. It seems to be working as expected.

Here's the snippet I'm using in its entirety:

"ElasticLoadBalancer" : {
  "Type" : "AWS::ElasticLoadBalancing::LoadBalancer",
  "Properties" : {
    "AvailabilityZones" : { "Fn::GetAZs" : "" },
    "CrossZone" : "true",
    "Listeners" : [ {
      "LoadBalancerPort" : "80",
      "InstancePort" : "80",
      "Protocol" : "HTTP"
    } ],
    "Tags" : [
    {
        "Key" : "Name",
        "Value" : { "Fn::Join" : [ "-", [ { "Ref" : "AWS::StackName" }, "MyELB"] ] }
    }
    ]
  }
},

The one noticeable difference I see in yours is that you're missing some of the quotes around the Tag stanza.

Answer 2

I feel foolish, the name tags are set correctly, I was looking at the physical IDs, not the name tags. The docs explaining how to control physical IDs are here .

Thanks to @alanwill for testing, and forcing me to go back through all the steps carefully!