Implement Conditional Properties in AWS CloudFormation

The following CloudFormation snippet shows how to use conditional properties in an CloudFormation template. The example configures one or two subnets in the VPCOptions section of an Elasticsearch domain, depending on whether a parameter called ZoneAwareness is set to true or not.

Parameters:
 ZoneAwareness:
      Type: String
      AllowedValues: [true, false]
      Default: true

Conditions:
  ZoneAwarenessTrue: !Equals [!Ref ZoneAwareness, true]

  ElasticsearchDomain:
    Type: AWS::Elasticsearch::Domain
    Properties:
      ...
      VPCOptions:
        SubnetIds: 
          -  !Ref SubnetA
          - Fn::If:
            - ZoneAwarenessTrue
            -  !Ref SubnetB
            - !Ref "AWS::NoValue"
        SecurityGroupIds:
          - !Ref SecurityGroup