CloudFormation

Deploy AWS infrastructure with native CloudFormation templates, change sets, nested stacks, and drift detection.

When to Use This Skill

• Deploying AWS resources using AWS-native Infrastructure as Code
• Creating repeatable, parameterized infrastructure templates
• Managing multi-environment deployments (dev, staging, prod) with the same template
• Implementing safe deployments with change sets and rollback protection
• Detecting and remediating configuration drift
• Organizing large infrastructure into nested stacks
• Exporting/importing values between stacks

Prerequisites

• AWS CLI v2 installed and configured
• IAM permissions: cloudformation:*, plus permissions for all resources in the template
• (Optional) cfn-lint installed for template validation (pip install cfn-lint)
• S3 bucket for storing templates larger than 51,200 bytes

Template Structure

AWSTemplateFormatVersion: '2010-09-09'
Description: Production web application infrastructure

Metadata:
  AWS::CloudFormation::Interface:
    ParameterGroups:
      - Label: { default: "Environment" }
        Parameters: [Environment, InstanceType]
      - Label: { default: "Network" }
        Parameters: [VpcId, SubnetIds]

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

  InstanceType:
    Type: String
    Default: t3.micro
    AllowedValues: [t3.micro, t3.small, t3.medium, t3.large]

  VpcId:
    Type: AWS::EC2::VPC::Id
    Description: VPC to deploy into

  SubnetIds:
    Type: List<AWS::EC2::Subnet::Id>
    Description: Subnets for the application

Conditions:
  IsProd: !Equals [!Ref Environment, prod]
  CreateReadReplica: !Equals [!Ref Environment, prod]

Mappings:
  RegionAMI:
    us-east-1:
      AL2023: ami-0abcdef1234567890
    us-west-2:
      AL2023: ami-0fedcba9876543210

Resources:
  SecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: !Sub '${Environment}-web-sg'
      VpcId: !Ref VpcId
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 443
          ToPort: 443
          CidrIp: 0.0.0.0/0
      Tags:
        - Key: Name
          Value: !Sub '${Environment}-web-sg'

  LaunchTemplate:
    Type: AWS::EC2::LaunchTemplate
    Properties:
      LaunchTemplateName: !Sub '${Environment}-web'
      LaunchTemplateData:
        ImageId: !FindInMap [RegionAMI, !Ref 'AWS::Region', AL2023]
        InstanceType: !If [IsProd, t3.large, !Ref InstanceType]
        MetadataOptions:
          HttpTokens: required
        SecurityGroupIds:
          - !Ref SecurityGroup

  AutoScalingGroup:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      AutoScalingGroupName: !Sub '${Environment}-web-asg'
      LaunchTemplate:
        LaunchTemplateId: !Ref LaunchTemplate
        Version: !GetAtt LaunchTemplate.LatestVersionNumber
      MinSize: !If [IsProd, 2, 1]
      MaxSize: !If [IsProd, 10, 3]
      DesiredCapacity: !If [IsProd, 4, 1]
      VPCZoneIdentifier: !Ref SubnetIds
      TargetGroupARNs:
        - !Ref TargetGroup
      HealthCheckType: ELB
      HealthCheckGracePeriod: 300
      Tags:
        - Key: Name
          Value: !Sub '${Environment}-web'
          PropagateAtLaunch: true
    UpdatePolicy:
      AutoScalingRollingUpdate:
        MinInstancesInService: !If [IsProd, 2, 0]
        MaxBatchSize: 1
        PauseTime: PT5M
        WaitOnResourceSignals: true
        SuspendProcesses:
          - HealthCheck
          - ReplaceUnhealthy
          - AZRebalance
          - AlarmNotification
          - ScheduledActions

  TargetGroup:
    Type: AWS::ElasticLoadBalancingV2::TargetGroup
    Properties:
      Name: !Sub '${Environment}-web-tg'
      Port: 8080
      Protocol: HTTP
      VpcId: !Ref VpcId
      TargetType: instance
      HealthCheckPath: /health
      HealthCheckIntervalSeconds: 30
      HealthyThresholdCount: 2
      UnhealthyThresholdCount: 3

Outputs:
  SecurityGroupId:
    Description: Web security group ID
    Value: !Ref SecurityGroup
    Export:
      Name: !Sub '${Environment}-WebSecurityGroup'

  AutoScalingGroupName:
    Description: ASG name
    Value: !Ref AutoScalingGroup
    Export:
      Name: !Sub '${Environment}-WebASG'

Stack Operations

# Validate a template
aws cloudformation validate-template --template-body file://template.yaml

# Lint with cfn-lint (catches more issues)
cfn-lint template.yaml

# Create a stack
aws cloudformation create-stack \

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