AWS CloudFormation Security Infrastructure

Overview

Create production-ready security infrastructure using AWS CloudFormation templates. This skill covers KMS encryption, Secrets Manager, IAM security with least privilege, VPC security configurations, ACM certificates, parameter security, secure outputs, cross-stack references, CloudWatch Logs encryption, defense in depth strategies, and security best practices.

When to Use

Implementing KMS encryption at rest and in transit
Managing secrets with Secrets Manager and automatic rotation
Applying IAM least privilege policies and permission boundaries
Securing VPC with security groups, NACLs, and VPC endpoints
Managing TLS/SSL certificates with ACM
Encrypting CloudWatch Logs and S3 buckets
Creating secure cross-stack references and outputs

Instructions

Follow these steps to create security infrastructure with CloudFormation:

1. Define KMS Encryption Keys

Create customer-managed keys for encryption:

Resources:
  EncryptionKey:
    Type: AWS::KMS::Key
    Properties:
      Description: Customer-managed key for data encryption
      KeyPolicy:
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action:
              - kms:Decrypt
              - kms:GenerateDataKey
            Resource: "*"
          - Effect: Allow
            Principal:
              AWS: !Sub "arn:aws:iam::${AWS::AccountId}:root"
            Action:
              - kms:*
            Resource: "*"

  KeyAlias:
    Type: AWS::KMS::Alias
    Properties:
      AliasName: !Sub "${AWS::StackName}/encryption-key"
      TargetKeyId: !Ref EncryptionKey

Validate: aws kms get-key-policy --key-id <key-id> --output text

2. Manage Secrets with Secrets Manager

Store and retrieve sensitive data securely:

Resources:
  DatabaseSecret:
    Type: AWS::SecretsManager::Secret
    Properties:
      Name: !Sub "${AWS::StackName}/database"
      Description: Database credentials
      SecretString: !Sub |
        {
          "username": "admin",
          "password": "${DatabasePassword}",
          "engine": "mysql",
          "host": "${DatabaseEndpoint}",
          "port": 3306
        }
      KmsKeyId: !Ref EncryptionKey

  SecretRotationSchedule:
    Type: AWS::SecretsManager::RotationSchedule
    Properties:
      SecretId: !Ref DatabaseSecret
      RotationLambdaARN: !Ref RotationLambda.Arn
      RotationRules:
        AutomaticallyAfterDays: 30

Validate: aws secretsmanager describe-secret --secret-id <secret-name>

3. Apply IAM Least Privilege

Create roles and policies with minimal required permissions:

Resources:
  ExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: "2012-10-17"
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Policies:
        - PolicyName: SpecificPermissions
          PolicyDocument:
            Version: "2012-10-17"
            Statement:
              - Effect: Allow
                Action:
                  - s3:GetObject
                Resource: !Sub "${DataBucket.Arn}/*"

Validate: aws iam simulate-principal-policy --policy-source-arn <role-arn> --action-names s3:GetObject --resource-arns <bucket-arn>

4. Secure VPC Configuration

Implement network security with security groups and NACLs:

Resources:
  ApplicationSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Application security group
      VpcId: !Ref VPC
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 443
          ToPort: 443
          SourceSecurityGroupId: !Ref LoadBalancerSecurityGroup
      SecurityGroupEgress:
        - IpProtocol: -1
          CidrIp: 0.0.0.0/0

  ApplicationNACL:
    Type: AWS::EC2::NetworkAcl
    Properties:
      VpcId: !Ref VPC

  NACLEntry:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
      NetworkAclId: !Ref ApplicationNACL
      RuleNumber: 100
      Protocol: "6"
      RuleAction: allow
      Egress: false
      CidrBlock: 0.0.0.0/0
      PortRange:
        From: 443
        To: 443

Validate: aws ec2 describe-security-groups --group-ids <sg-id> --query 'SecurityGroups[0].IpPermissions'

5. Request ACM Certificates

Manage TLS/SSL certificates for secure communication:

Resources:
  Certificate:
    Type: AWS::ACM::Certificate
    Properties:
      DomainName: !Ref DomainName
      SubjectAlternativeNames:
        - !Sub "www.${DomainName}"
        - !Sub "api.${DomainName}"
      DomainValidationOptions:
        - DomainName: !Ref DomainName
          ValidationDomain: !Ref DomainName
      Tags:
        - Key: Environment
          Value: !Ref Environment

  # DNS validation record
  DnsValidationRecord:
    Type: AWS::Route53::RecordSet
    Properties:
      HostedZoneName: !Ref HostedZone
      Name: !Sub "_${DomainName}."
      Type: CNAME
      TTL: 300
      ResourceRecords:
        - !Ref Certificate

Validate: aws acm describe-certificate --certificate-arn <arn> --query 'Certificate.Status'

6. Implement Secure Parameters

Use SecureString for sensitive parameter values:

Resources:
  DatabasePasswordParameter:
    Type: AWS::SSM::Parameter
    Properties:
      Name: !Sub "/${AWS::StackName}/database/password"
      Type: SecureString
      Value: !Ref DatabasePassword
      Description: Database master password
      KmsKeyId: !Ref EncryptionKey

  # Reference in other resources
  DatabaseInstance:
    Type: AWS::RDS::DBInstance
    Properties:
      MasterUsername: admin
      MasterUserPassword: !Ref DatabasePasswordParameter

Validate: aws ssm get-parameter --name <param-name> --with-decryption --query 'Parameter.Type'

7. Create Secure Outputs

Export only non-sensitive values from stacks:

Outputs:
  # Safe to export
  KMSKeyArn:
    Description: KMS Key ARN for encryption
    Value: !GetAtt EncryptionKey.Arn
    Export:
      Name: !Sub "${AWS::StackName}-KMSKeyArn"

  SecretArn:
    Description: Secret ARN (not the secret value)
    Value: !Ref DatabaseSecret
    Export:
      Name: !Sub "${AWS::StackName}-SecretArn"

  # DO NOT export sensitive data
  # Incorrect:
  # SecretValue:
  #   Value: !GetAtt DatabaseSecret.SecretString

Validate: aws cloudformation list-exports --query "Exports[?Name=='<stack-name>-KMSKeyArn']"

8. Encrypt CloudWatch Logs

Enable encryption for log groups:

Resources:
  EncryptedLogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName: !Sub "/aws/applications/${ApplicationName}"
      RetentionInDays: 30
      KmsKeyId: !Ref EncryptionKey

Validate: aws logs describe-log-groups --log-group-name-prefix <prefix> --query 'logGroups[0].kmsKeyId'

Best Practices

KMS: Use separate keys per data classification; enable annual key rotation; use customer-managed keys for compliance
Secrets: Rotate automatically (30 days for databases); never store secrets in plain text; use IAM policies for access control
IAM: Apply least privilege; use roles not access keys; enable MFA; implement permission boundaries
Network: Prefer security groups over NACLs; use VPC endpoints; restrict by specific CIDR ranges
Certificates: Use ACM for automatic renewal; DNS validation is faster than email
Encryption: Encrypt at rest and in transit; TLS 1.2+ required; use SSE-KMS for S3

Examples

Complete KMS and Secrets Stack

Resources:
  # KMS Key with proper policy
  AppKey:
    Type: AWS::KMS::Key
    Properties:
      KeyPolicy:
        Statement:
          - Effect: Allow
            Principal:
              AWS: !Sub "arn:aws:iam::${AWS::AccountId}:root"
            Action: kms:*
            Resource: "*"
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action:
              - kms:Decrypt
              - kms:GenerateDataKey
            Resource: "*"

  # Secrets Manager with rotation
  DbSecret:
    Type: AWS::SecretsManager::Secret
    Properties:
      SecretString: !Sub '{"password":"${DbPassword}"}'
      KmsKeyId: !Ref AppKey
      RotationRules:
        AutomaticallyAfterDays: 30

IAM Least Privilege Role

Resources:
  LambdaRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: "2012-10-17"
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      Policies:
        - PolicyName: AccessPolicy
          PolicyDocument:
            Statement:
              - Effect: Allow
                Action: s3:GetObject
                Resource: !Sub "${Bucket.Arn}/*"

For comprehensive examples with VPC security groups, ACM certificates, and complete encrypted infrastructure stacks, see examples.md.

Constraints and Warnings

Resource Limits

Security groups: max 60 inbound + 60 outbound rules
NACLs: max 20 inbound + 20 outbound rules per subnet
VPCs: max 5 per region (soft limit)
Key rotation: annual for KMS customer-managed keys

Security Constraints

NACLs are stateless: return traffic must be explicitly allowed
Default security groups cannot be deleted
Security group references cannot span VPC peering (use CIDR)
Cross-account access requires both IAM and resource policies

Operational Warnings

Secrets rotation requires Lambda function with proper IAM permissions
KMS key deletion requires pending window (7-30 days)
ACM certificates need DNS validation before issuance
VPC CIDR blocks cannot overlap with peered VPCs

For detailed constraints including cost considerations and quota management, see constraints.md.

References

For detailed implementation guidance, see:

examples.md - Complete KMS stacks, Secrets Manager with rotation, IAM least privilege roles, VPC security groups, ACM certificates, and encrypted infrastructure
constraints.md - Resource limits, security constraints, operational constraints, network constraints, cost considerations, and access control constraints