AWS Cloudformation S3 Agent Skill

AWS CloudFormation S3 Patterns

Provides S3 bucket configurations, policies, versioning, lifecycle rules, and CloudFormation template structure best practices for production-ready infrastructure.

When to Use

• Creating S3 buckets with custom configurations
• Implementing bucket policies for access control
• Configuring S3 versioning for data protection
• Setting up lifecycle rules for data management
• Creating Outputs for cross-stack references
• Using Parameters with AWS-specific types
• Organizing templates with Mappings and Conditions

Overview

S3 bucket configurations, policies, versioning, lifecycle rules, and CloudFormation template structure for production-ready infrastructure.

Instructions

• Define Bucket Resources: Create AWS::S3::Bucket with versioning, encryption, PublicAccessBlock
• Configure Bucket Policy: Set up IAM policies for access control
• Set Up Lifecycle Rules: Define transitions and expiration policies
• Configure CORS: Allow cross-origin requests if needed
• Add Outputs: Export bucket names/ARNs for cross-stack references

Validate before deploy:

aws cloudformation validate-template --template-body file://template.yaml

Deploy with rollback on failure:

aws cloudformation deploy \
  --template-file template.yaml \
  --stack-name my-s3-stack \
  --capabilities CAPABILITY_IAM

If deployment fails, CloudFormation automatically rolls back. Check failures with:

aws cloudformation describe-stack-events --stack-name my-s3-stack

Quick Reference

| Resource Type | Purpose |

|---------------|---------|

| AWS::S3::Bucket | Create S3 bucket |

| AWS::S3::BucketPolicy | Set bucket-level policies |

| AWS::S3::BucketReplication | Cross-region replication |

| Parameters | Input values for customization |

| Mappings | Static configuration tables |

| Conditions | Conditional resource creation |

| Outputs | Return values for cross-stack references |

Examples

Basic S3 Bucket

Resources:
  DataBucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: my-data-bucket

Bucket with Versioning and Encryption

DataBucket:
  Type: AWS::S3::Bucket
  Properties:
    BucketName: !Sub "${AWS::StackName}-data"
    VersioningConfiguration:
      Status: Enabled
    BucketEncryption:
      ServerSideEncryptionConfiguration:
        - ServerSideEncryptionByDefault:
            SSEAlgorithm: AES256
    PublicAccessBlockConfiguration:
      BlockPublicAcls: true
      BlockPublicPolicy: true

Lifecycle Rule

DataBucket:
  Type: AWS::S3::Bucket
  Properties:
    LifecycleConfiguration:
      Rules:
        - Id: ArchiveOldData
          Status: Enabled
          Transitions:
            - StorageClass: GLACIER
              TransitionInDays: 365

Bucket Policy

BucketPolicy:
  Type: AWS::S3::BucketPolicy
  Properties:
    Bucket: !Ref DataBucket
    PolicyDocument:
      Statement:
        - Effect: Allow
          Principal:
            AWS: !Ref RoleArn
          Action:
            - s3:GetObject
          Resource: !Sub "${DataBucket.Arn}/*"

See references/complete-examples.md for more complete examples including CORS, static websites, replication, and production-ready configurations.

Template Structure

Template Sections

AWSTemplateFormatVersion: 2010-09-09
Description: Template description

Mappings: {}       # Static configuration tables
Metadata: {}       # Additional information
Parameters: {}     # Input values
Conditions: {}     # Conditional creation
Transform: {}      # Macro processing
Resources: {}      # AWS resources (REQUIRED)
Outputs: {}        # Return values

Parameters

Parameters:
  BucketName:
    Type: String
    Description: S3 bucket name
    Default: my-bucket
    MinLength: 3
    MaxLength: 63
    AllowedPattern: '^[a-z0-9-]+$'

Conditions

Conditions:
  IsProduction: !Equals [!Ref Environment, prod]
  ShouldEnableVersioning: !Equals [!Ref EnableVersioning, 'true']

Resources:
  DataBucket:
    Type: AWS::S3::Bucket
    Properties:
      VersioningConfiguration:
        Status: !If [ShouldEnableVersioning, Enabled, Suspended]

Outputs

Outputs:
  BucketName:
    Description: Name of the S3 bucket
    Value: !Ref DataBucket
    Export:
      Name: !Sub '${AWS::StackName}-BucketName'

See references/advanced-configuration.md for detailed Mappings, Conditions, Parameters, and cross-stack references.

Best Practices

• Public Access Block: Always enable for non-static website buckets
• Versioning: Enable for critical data to prevent accidental deletion
• Bucket Policies: Use instead of ACLs for access control
• Lifecycle Rules: Implement cost optimization with tiering
• Encryption: Enable default encryption (SSE-KMS or AES256)
• Tags: Tag all resources for organization and cost allocation
• Outputs: Export bucket names/ARNs for cross-stack references
• Parameters: Use parameters for reusability across environments

Common Troubleshooting

Bucket already exists: Use unique bucket names with CloudFormation stack name

Access denied: Verify bucket policy and IAM permissions

Versioning conflicts: Cannot suspend versioning once objects exist

Lifecycle not working: Check rule status and prefix filters

Cross-stack references: Ensure outputs are exported before importing

Related Skills

• aws-cloudformation-security - Security best practices for S3
• aws-cloudformation-lambda - Lambda triggers for S3 events
• aws-cloudformation-iam - IAM roles for S3 access

References

Complete Examples

• references/complete-examples.md - Basic buckets, versioning, lifecycle, CORS, policies, production stacks, event notifications, static websites, replication

Advanced Configuration

• references/advanced-configuration.md - Parameters, Mappings, Conditions, Outputs, Metadata, DeletionPolicy, DependsOn, Transform

Constraints and Warnings

• Bucket names: Must be globally unique (across all AWS accounts)
• Versioning: Cannot be suspended once objects exist in bucket
• Lifecycle rules: Minimum 1 day for expiration, 0 days for transitions
• Bucket policies: Limited to 20 KB in size
• Public access: Blocked by default; requires explicit configuration
• CORS: Limited to 100 rules per bucket
• Replication: Versioning must be enabled on both source and destination
• Encryption: KMS keys must be in same region as bucket
• Tags: Maximum 50 tags per resource
• Stack limits: CloudFormation limits resources per stack (200 default)