AWS - Cloud Formation Elements & Templates

 An AWS CloudFormation template is a JSON or YAML formatted text file. It usually contains these main sections:

1. AWSTemplateFormatVersion (optional)

   • The template version (latest = "2010-09-09").

2. Description (optional)

   • Human-readable description of the template’s purpose.

3. Metadata (optional)

   • Additional information about the template (can be used by tools).

4. Parameters (optional)

   • Input values that let you customize templates at runtime.

5. Mappings (optional)

   • Hardcoded lookup tables (e.g., AMI IDs per region).

6. Conditions (optional)

   • Control resource creation depending on parameter values or other logic.

7. Transform (optional)

   • For including and processing macros (like AWS::Include or AWS::Serverless).

8. Resources (required) 

   • The core section – defines the AWS resources (EC2, S3, Lambda, etc.) that CloudFormation creates and manages.

9. Outputs (optional)

• Values you want to return (e.g., VPC ID, Load Balancer DNS, etc.).

Example 1: Minimal Template (S3 Bucket) — JSON

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "Simple S3 bucket example",
  "Resources": {
    "MyS3Bucket": {
      "Type": "AWS::S3::Bucket",
      "Properties": {
        "BucketName": "my-sample-bucket-12345"
      }
    }
  }
}

Example 2: EC2 Instance with Parameters — JSON
{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "Launch an EC2 instance with a KeyPair",
  "Parameters": {
    "KeyName": {
      "Description": "Name of an existing EC2 KeyPair",
      "Type": "AWS::EC2::KeyPair::KeyName"
    }
  },
  "Resources": {
    "MyEC2Instance": {
      "Type": "AWS::EC2::Instance",
      "Properties": {
        "InstanceType": "t2.micro",
        "ImageId": "ami-0c02fb55956c7d316",
        "KeyName": {
          "Ref": "KeyName"
        }
      }
    }
  },
  "Outputs": {
    "InstanceId": {
      "Description": "EC2 Instance ID",
      "Value": {
        "Ref": "MyEC2Instance"
      }
    }
  }
}

Example 3: Using Mappings + Conditions — JSON
{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "EC2 with region-specific AMIs",
  "Mappings": {
    "RegionMap": {
      "us-east-1": {
        "AMI": "ami-0c02fb55956c7d316"
      },
      "us-west-2": {
        "AMI": "ami-08962a4068733a2b6"
      }
    }
  },
  "Parameters": {
    "EnvType": {
      "Type": "String",
      "AllowedValues": ["dev", "prod"]
    }
  },
  "Conditions": {
    "CreateProdResources": {
      "Fn::Equals": [
        { "Ref": "EnvType" },
        "prod"
      ]
    }
  },
  "Resources": {
    "MyEC2Instance": {
      "Type": "AWS::EC2::Instance",
      "Condition": "CreateProdResources",
      "Properties": {
        "InstanceType": "t2.micro",
        "ImageId": {
          "Fn::FindInMap": [
            "RegionMap",
            { "Ref": "AWS::Region" },
            "AMI"
          ]
        }
      }
    }
  }
}