CloudFormation - Infrastructure as Code

What is CloudFormation?

CloudFormation allows you to define AWS infrastructure as code using JSON or YAML templates. This enables version control, repeatability, and automation of infrastructure provisioning.

Key Concepts

Template - JSON or YAML file defining resources Stack - Collection of AWS resources created from a template Change Set - Preview of changes before updating a stack

CloudFormation Template Structure

AWSTemplateFormatVersion: '2010-09-09'
Description: 'CloudFormation template description'

Parameters:
  # Input parameters

Resources:
  # AWS resources to create

Outputs:
  # Values to export

Basic Example: EC2 Instance

AWSTemplateFormatVersion: '2010-09-09'
Description: 'Simple EC2 instance'

Parameters:
  InstanceType:
    Type: String
    Default: t3.micro
    AllowedValues:
      - t3.micro
      - t3.small
      - t3.medium
    Description: EC2 instance type

  KeyName:
    Type: AWS::EC2::KeyPair::KeyName
    Description: SSH key pair name

Resources:
  MyEC2Instance:
    Type: AWS::EC2::Instance
    Properties:
      InstanceType: !Ref InstanceType
      ImageId: ami-0c55b159cbfafe1f0  # Amazon Linux 2 (us-east-1)
      KeyName: !Ref KeyName
      SecurityGroupIds:
        - !Ref MySecurityGroup
      Tags:
        - Key: Name
          Value: MyWebServer

  MySecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Allow SSH and HTTP
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 22
          ToPort: 22
          CidrIp: 0.0.0.0/0
        - IpProtocol: tcp
          FromPort: 80
          ToPort: 80
          CidrIp: 0.0.0.0/0

Outputs:
  InstanceId:
    Description: Instance ID
    Value: !Ref MyEC2Instance
  PublicIP:
    Description: Public IP address
    Value: !GetAtt MyEC2Instance.PublicIp

VPC with Public and Private Subnets

AWSTemplateFormatVersion: '2010-09-09'
Description: 'VPC with public and private subnets'

Resources:
  MyVPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: 10.0.0.0/16
      EnableDnsHostnames: true
      EnableDnsSupport: true
      Tags:
        - Key: Name
          Value: MyVPC

  PublicSubnet:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref MyVPC
      CidrBlock: 10.0.1.0/24
      AvailabilityZone: !Select [0, !GetAZs '']
      MapPublicIpOnLaunch: true
      Tags:
        - Key: Name
          Value: Public Subnet

  PrivateSubnet:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref MyVPC
      CidrBlock: 10.0.2.0/24
      AvailabilityZone: !Select [0, !GetAZs '']
      Tags:
        - Key: Name
          Value: Private Subnet

  InternetGateway:
    Type: AWS::EC2::InternetGateway
    Properties:
      Tags:
        - Key: Name
          Value: MyIGW

  AttachGateway:
    Type: AWS::EC2::VPCGatewayAttachment
    Properties:
      VpcId: !Ref MyVPC
      InternetGatewayId: !Ref InternetGateway

  PublicRouteTable:
    Type: AWS::EC2::RouteTable
    Properties:
      VpcId: !Ref MyVPC
      Tags:
        - Key: Name
          Value: Public Route Table

  PublicRoute:
    Type: AWS::EC2::Route
    DependsOn: AttachGateway
    Properties:
      RouteTableId: !Ref PublicRouteTable
      DestinationCidrBlock: 0.0.0.0/0
      GatewayId: !Ref InternetGateway

  SubnetRouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref PublicSubnet
      RouteTableId: !Ref PublicRouteTable

Outputs:
  VPCId:
    Description: VPC ID
    Value: !Ref MyVPC
    Export:
      Name: !Sub '${AWS::StackName}-VPC'

  PublicSubnetId:
    Description: Public Subnet ID
    Value: !Ref PublicSubnet
    Export:
      Name: !Sub '${AWS::StackName}-PublicSubnet'

Deploying CloudFormation Stacks

Using AWS CLI:

# Create stack
aws cloudformation create-stack \
  --stack-name my-stack \
  --template-body file://template.yaml \
  --parameters ParameterKey=KeyName,ParameterValue=my-key

# Update stack
aws cloudformation update-stack \
  --stack-name my-stack \
  --template-body file://template.yaml

# Delete stack
aws cloudformation delete-stack \
  --stack-name my-stack

# Describe stack
aws cloudformation describe-stacks \
  --stack-name my-stack

# List all stacks
aws cloudformation list-stacks

Using AWS Console:

1. Navigate to CloudFormation service
2. Click "Create stack"
3. Upload template file or paste template
4. Enter stack name and parameters
5. Review and create

CloudFormation Best Practices

1. Use Parameters for Flexibility

Parameters:
  Environment:
    Type: String
    Default: dev
    AllowedValues: [dev, staging, prod]

2. Use Intrinsic Functions

# !Ref - Reference parameters or resources
InstanceType: !Ref InstanceTypeParameter

# !GetAtt - Get attribute of resource
PublicIp: !GetAtt MyEC2Instance.PublicIp

# !Sub - String substitution
Name: !Sub '${AWS::StackName}-instance'

# !Join - Join strings
SecurityGroupIds: !Join [',', !Ref SecurityGroups]

3. Export Values for Cross-Stack References

Outputs:
  VPCId:
    Value: !Ref MyVPC
    Export:
      Name: SharedVPC

# In another stack:
Resources:
  MyInstance:
    Type: AWS::EC2::Instance
    Properties:
      SubnetId: !ImportValue SharedVPC

4. Use Nested Stacks for Modularity

Resources:
  NetworkStack:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: https://s3.amazonaws.com/bucket/network.yaml
      Parameters:
        VPCCidr: 10.0.0.0/16

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Master Infrastructure as Code with CloudFormation for repeatable, version-controlled AWS deployments!