AWS CloudFormation is a service that helps you model and set up your AWS resources using Infrastructure as Code (IaC). It solves several key problems:

• Manual Configuration Errors: Eliminates human error in manual resource provisioning
• Environment Consistency: Ensures identical infrastructure across development, testing, and production
• Resource Dependencies: Automatically handles the order of resource creation and dependencies
• Version Control: Infrastructure changes can be tracked and versioned like application code
• Rollback Capabilities: Provides automatic rollback if stack creation/update fails
• Cost Management: Easy to tear down entire environments, reducing costs
• Documentation: Templates serve as living documentation of your infrastructure

The main components are:

1. AWSTemplateFormatVersion (Optional): Specifies the template format version
2. Description (Optional): Human-readable description of the template
3. Parameters (Optional): Input values for the template
4. Mappings (Optional): Static lookup tables
5. Conditions (Optional): Controls resource creation based on conditions
6. Resources (Required): AWS resources to create
7. Outputs (Optional): Values returned when viewing stack properties

AWSTemplateFormatVersion: '2010-09-09'
Description: 'Simple web server template'
Parameters:
  InstanceType:
    Type: String
    Default: t2.micro
Resources:
  WebServer:
    Type: AWS::EC2::Instance
    Properties:
      InstanceType: !Ref InstanceType
      ImageId: ami-0abcdef1234567890
Outputs:
  InstanceId:
    Value: !Ref WebServer

YAML Advantages:

• More human-readable and concise
• Supports comments for documentation
• Better for complex templates
• Less prone to syntax errors (no missing commas/brackets)
  JSON Advantages:
• Smaller file size
• Faster parsing
• Better tool support in some IDEs
• More familiar to developers
  Example comparison:

# YAML
Resources:
  MyBucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: my-example-bucket

{
  "Resources": {
    "MyBucket": {
      "Type": "AWS::S3::Bucket",
      "Properties": {
        "BucketName": "my-example-bucket"
      }
    }
  }
}

Most teams prefer YAML for readability and maintainability.

When stack creation fails:

1. Automatic Rollback: CloudFormation automatically deletes all successfully created resources
2. Stack State: Stack goes to ROLLBACK_COMPLETE state
3. Error Information: Detailed error messages available in Events tab
4. Billing: You're only charged for resources that existed during the failed creation period
   Prevention strategies:

• Validate templates before deployment
• Use --disable-rollback flag only for debugging
• Implement proper IAM permissions
• Check service limits and quotas
• Use change sets for updates
  Example debugging:

aws cloudformation describe-stack-events --stack-name my-stack

CloudFormation supports these parameter types:
Basic Types:

• String: Text values
• Number: Numeric values
• CommaDelimitedList: List of values separated by commas
  AWS-Specific Types:
• AWS::EC2::KeyPair::KeyName: EC2 Key Pair names
• AWS::EC2::SecurityGroup::Id: Security Group IDs
• AWS::EC2::Subnet::Id: Subnet IDs
• AWS::EC2::VPC::Id: VPC IDs
• AWS::Route53::HostedZone::Id: Route 53 Hosted Zone IDs
  Lists:
• List<Number>: List of numbers
• List<AWS::EC2::Subnet::Id>: List of subnet IDs
  Example:

Parameters:
  Environment:
    Type: String
    AllowedValues: [dev, staging, production]
    Default: dev
  SubnetIds:
    Type: List<AWS::EC2::Subnet::Id>
    Description: Subnets for load balancer
  InstanceCount:
    Type: Number
    MinValue: 1
    MaxValue: 10
    Default: 2

CloudFormation:

• AWS-native service, deeply integrated with AWS APIs
• Uses JSON or YAML templates
• State management handled by AWS
• No additional cost (only pay for AWS resources created)
• Eventually consistent with AWS service updates
• Limited to AWS ecosystem
  Terraform:
• Third-party tool supporting multiple cloud providers
• Uses HCL (HashiCorp Configuration Language)
• Requires state file management
• Licensed software with enterprise features
• Often gets new provider features faster
• Multi-cloud support
  When to choose CloudFormation:
• Pure AWS environments
• Teams already invested in AWS ecosystem
• Want AWS-managed state and lifecycle
• Need deep integration with AWS services