---
AWSTemplateFormatVersion: "2010-09-09"
Parameters:
  myEnvironment:
    Type: String
    Default: dev
  myCondition:
    Type: String
    Default: isDevelopment
Conditions:
  isProduction: !Equals [!Ref myEnvironment, "prd"]
  isDevelopment: !Equals [!Ref myEnvironment, "dev"]
Resources:
  myInstance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !If [!Ref myCondition, "ami-123456", "ami-abcdef"]
  myInstance2:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !If [myCondition, "ami-123456"]
  myInstance3:
    Type: AWS::EC2::Instance
    Properties:
      ImageId:
        Fn::If:
          myCondition:
            - "ami-123456"
            - "ami-abcdef"