Outputs are not getting generated based on condition - amazon-web-services

Question

In my cf template I have set of conditions defined and those conditions are invoked in the resource section as well however when i try to generate outputs using the conditions its not working as expected.
{
"AWSTemplateFormatVersion": "2010-09-09",
"Description": "CloudFormation to Deploy EMR clusters",
"Parameters": {
"Applications": {
"Default": "Core Hadoop",
"Description": "Installed Applications",
"Type": "String",
"AllowedValues" : ["Core Hadoop","HBase"],
"ConstraintDescription": "Must be valid Applications"
},
"awsRegion": {
"Default" : "<my-region>",
"Description": "awsRegion",
"Type": "String"
},
"Ec2KeyName": {
"Default": "<my-key.pem>",
"Description": "Ec2KeyName",
"Type": "String"
}
},
"Resources": {
"EMRCluster1": {
"Type" : "AWS::EMR::Cluster",
"Condition" : "CH",
"Properties" : {
"Applications" : [
{
"Name": "Hadoop"
},
{
"Name": "Hive"
},
{
"Name": "Hue"
},
{
"Name": "Pig"
},
{
"Name": "Mahout"
},
{
"Name": "Tez"
}
]
}
}
"EMRCluster2": {
"Type" : "AWS::EMR::Cluster",
"Condition" : "HB",
"Properties" : {
"Applications": [
{
"Name": "Hadoop"
},
{
"Name": "Hive"
},
{
"Name": "Hue"
},
{
"Name": "HBase"
},
{
"Name": "Phoenix"
},
{
"Name": "ZooKeeper"
}
]
}
}
}
"Conditions" : {
"CH" : {"Fn::Equals" : [{"Ref" : "Applications"}, "Core Hadoop"]},
"HB" : {"Fn::Equals" : [{"Ref" : "Applications"}, "HBase"]}
},
"Outputs": {
"MasterPublicDnsName": {
"Condition" : "CH",
"Value": {
"Fn::GetAtt": [
"EMRCluster1",
"MasterPublicDNS"
]
},
"Description": "MasterPublicDNS for cluster"
},
"MasterPublicDnsName": {
"Condition" : "HB",
"Value": {
"Fn::GetAtt": [
"EMRCluster2",
"MasterPublicDNS"
]
},
"Description": "MasterPublicDNS for cluster"
}
}
Expected: If i choose "CH" in the parameters then it should give cluster1 masterdns and if i choose "HB" it should provide cluster2's masterdns
Actual: If i choose "HB" which is the last section in output, it will give me the masterdns of cluster2 however if i choose "CH" outputs section in cloudformation gives me "No outputs found.".
Can somebody help me on this please.

Answer 1

The problem probably exists because you are using the same name for both outputs. Since the behaviour of JSON with duplicate keys is undefined, the implementing language can choose how to behave in this situation. Presumably, the second time you are using the MasterPublicDnsName as the output name, you are overwriting the first name, which is consistent with the behaviour you are seeing.
You can either opt to use two different names, but this might makes using cross-stack references difficult, or use an Fn::If statement in the value of the output:
"Fn::If": [condition_name, value_if_true, value_if_false]
Or in your case:
"Fn::If": ["CH", {"Fn::GetAtt": ["EMRCluster1", "MasterPublicDNS"]}, {"Fn::GetAtt": ["EMRCluster2", "MasterPublicDNS"]}]
If you need more than two options, you'll need to nest your Fn::If statements