CloudFormation templates consist of a number of parts, but these are the four we're going to concentrate on:

• Parameters
• Resources
• Outputs
• Mappings

Here's a short YAML example:

AWSTemplateFormatVersion: '2010-09-09' 
Parameters:
  EC2KeyName: 
    Type: String 
    Description: EC2 Key Pair to launch with 
Mappings: 
  RegionMap: 
    us-east-1: 
      AMIID: ami-9be6f38c 
    ap-southeast-2: 
      AMIID: ami-28cff44b

We declare a parameter and mappings to start the template. Mappings will be covered in Chapter 10, Advanced AWS CloudFormation. Next, we define Resources:

Resources: 
  ExampleEC2Instance: 
    Type: AWS:EC2::Instance 
    Properties: 
      InstanceType: t2.nano 
      UserData: 
        Fn::Base64: 
          Fn::Sub': |
            #!/bin/bash -ex
            /opt/aws/bin/cfn-signal '${ExampleWaitHandle}' 
      ImageId: 
        Fn::FindInMap: [ RegionMap, Ref: 'AWS::Region', AMIID ]   
      KeyName: 
        Ref: EC2KeyName 

Then, in the final section of the template, we define WaitHandle, WaitCondition, and Outputs:

  ExampleWaitHandle: 
    Type: AWS::CloudFormation::WaitConditionHandle 
    Properties: 
  ExampleWaitCondition: 
    Type: AWS::CloudFormation::WaitCondition 
    DependsOn: ExampleEC2Instance 
    Properties: 
      Handle: 
        Ref: ExampleWaitHandle 
      Timeout: 600 
Outputs: 
  ExampleOutput: 
    Value: 
      Fn::GetAtt: ExampleWaitCondition.Data 
    Description: The data signaled with the WaitCondition

Outputs give you a way to see things such as auto-generated names, and, in this case, the data from the wait condition.