tools-only AWS CloudFormation S3 Patterns
Create production-ready Amazon S3 infrastructure using AWS CloudFormation templates. This skill covers S3 bucket configurations, bucket policies, versioning, lifecycle rules, and template structure best practices.
When to Use
Use this skill when:
- 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
- Building reusable CloudFormation templates for S3
Quick Start
Basic S3 Bucket
AWSTemplateFormatVersion: 2010-09-09
Description: Simple S3 bucket with default settings
Resources:
DataBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: my-data-bucket
Tags:
- Key: Environment
Value: production
- Key: Project
Value: my-project
S3 Bucket with Versioning and Logging
AWSTemplateFormatVersion: 2010-09-09
Description: S3 bucket with versioning and access logging
Parameters:
BucketName:
Type: String
Description: Name of the S3 bucket
Resources:
DataBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Ref BucketName
VersioningConfiguration:
Status: Enabled
LoggingConfiguration:
DestinationBucketName: !Ref AccessLogBucket
LogFilePrefix: logs/
Tags:
- Key: Name
Value: !Ref BucketName
AccessLogBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Sub ${BucketName}-logs
AccessControl: LogDeliveryWrite
Outputs:
BucketName:
Description: Name of the S3 bucket
Value: !Ref DataBucket
BucketArn:
Description: ARN of the S3 bucket
Value: !GetAtt DataBucket.Arn
Template Structure
Template Sections Overview
AWS CloudFormation templates are JSON or YAML files with specific sections. Each section serves a purpose in defining your infrastructure.
AWSTemplateFormatVersion: 2010-09-09 # Required - template version
Description: Optional description string # Optional description
# Section order matters for readability but CloudFormation accepts any order
Mappings: {} # Static configuration tables
Metadata: {} # Additional information about resources
Parameters: {} # Input values for customization
Rules: {} # Parameter validation rules
Conditions: {} # Conditional resource creation
Transform: {} # Macro processing (e.g., AWS::Serverless)
Resources: {} # AWS resources to create (REQUIRED)
Outputs: {} # Return values after stack creation
Format Version
The AWSTemplateFormatVersion identifies the template version. Current version is 2010-09-09.
AWSTemplateFormatVersion: 2010-09-09
Description: My S3 CloudFormation Template
Description
Add a description to document the template's purpose. Must appear after the format version.
AWSTemplateFormatVersion: 2010-09-09
Description: >
This template creates an S3 bucket with versioning enabled
for data protection. It includes:
- Bucket with versioning configuration
- Lifecycle rules for data retention
- Server access logging
Metadata
Use Metadata for additional information about resources or parameters.
Metadata:
AWS::CloudFormation::Interface:
ParameterGroups:
- Label:
default: Bucket Configuration
Parameters:
- BucketName
- EnableVersioning
- Label:
default: Lifecycle Rules
Parameters:
- RetentionDays
ParameterLabels:
BucketName:
default: Bucket Name
EnableVersioning:
default: Enable Versioning
Resources Section
The Resources section is the only required section. It defines AWS resources to provision.
Resources:
DataBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: my-data-bucket
VersioningConfiguration:
Status: Enabled
PublicAccessBlockConfiguration:
BlockPublicAcls: true
BlockPublicPolicy: true
IgnorePublicAcls: true
RestrictPublicBuckets: true
Parameters
Parameter Types
Use AWS-specific parameter types for validation and easier selection in the console.
Parameters:
ExistingBucketName:
Type: AWS::S3::Bucket::Name
Description: Select an existing S3 bucket
BucketNamePrefix:
Type: String
Description: Prefix for new bucket names
SSM Parameter Types
Reference Systems Manager parameters for dynamic values.
Parameters:
LatestBucketPolicy:
Type: AWS::SSM::Parameter::Value<String>
Description: Latest bucket policy from SSM
Default: /s3/bucket-policy/latest
Parameter Constraints
Add constraints to validate parameter values.
Parameters:
BucketName:
Type: String
Description: Name of the S3 bucket
Default: my-bucket
AllowedPattern: ^[a-z0-9][a-z0-9-]*[a-z0-9]$
ConstraintDescription: Bucket names must be lowercase, numbers, or hyphens
RetentionDays:
Type: Number
Description: Number of days to retain objects
Default: 30
MinValue: 1
MaxValue: 365
ConstraintDescription: Must be between 1 and 365 days
Environment:
Type: String
Description: Deployment environment
Default: development
AllowedValues:
- development
- staging
- production
ConstraintDescription: Must be development, staging, or production
Mappings
Use Mappings for static configuration data based on regions or other factors.
Mappings:
RegionConfig:
us-east-1:
BucketPrefix: us-east-1
us-west-2:
BucketPrefix: us-west-2
eu-west-1:
BucketPrefix: eu-west-1
EnvironmentSettings:
development:
VersioningStatus: Suspended
RetentionDays: 7
staging:
VersioningStatus: Enabled
RetentionDays: 30
production:
VersioningStatus: Enabled
RetentionDays: 90
Resources:
DataBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Sub ${BucketPrefix}-${Environment}-data
VersioningConfiguration:
Status: !FindInMap [EnvironmentSettings, !Ref Environment, VersioningStatus]
Conditions
Use Conditions to conditionally create resources based on parameters.
Parameters:
EnableVersioning:
Type: String
Default: true
AllowedValues:
- true
- false
Environment:
Type: String
Default: development
AllowedValues:
- development
- staging
- production
CreateLifecycleRule:
Type: String
Default: true
AllowedValues:
- true
- false
Conditions:
ShouldEnableVersioning: !Equals [!Ref EnableVersioning, true]
IsProduction: !Equals [!Ref Environment, production]
ShouldCreateLifecycle: !Equals [!Ref CreateLifecycleRule, true]
Resources:
DataBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Sub ${Environment}-data-bucket
VersioningConfiguration:
Status: !If [ShouldEnableVersioning, Enabled, Suspended]
LifecycleRule:
Type: AWS::S3::Bucket
Condition: ShouldCreateLifecycle
Properties:
BucketName: !Sub ${Environment}-lifecycle-bucket
LifecycleConfiguration:
Rules:
- Status: Enabled
ExpirationInDays: !If
- IsProduction
- 90
- 30
NoncurrentVersionExpirationInDays: 30
Transform
Use Transform for macros like AWS::Serverless for SAM templates.
AWSTemplateFormatVersion: 2010-09-09
Transform: AWS::Serverless-2016-10-31
Description: SAM template with S3 bucket trigger
Resources:
ThumbnailFunction:
Type: AWS::Serverless::Function
Properties:
Handler: index.handler
Runtime: python3.9
CodeUri: function/
Events:
ImageUpload:
Type: S3
Properties:
Bucket: !Ref ImageBucket
Events: s3:ObjectCreated:*
ImageBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Sub ${AWS::StackName}-images
Outputs and Cross-Stack References
Basic Outputs
Outputs:
BucketName:
Description: Name of the S3 bucket
Value: !Ref DataBucket
BucketArn:
Description: ARN of the S3 bucket
Value: !GetAtt DataBucket.Arn
BucketDomainName:
Description: Domain name of the S3 bucket
Value: !GetAtt DataBucket.DomainName
BucketWebsiteURL:
Description: Website URL for the S3 bucket
Value: !GetAtt DataBucket.WebsiteURL
Exporting Values for Cross-Stack References
Export values so other stacks can import them.
Outputs:
BucketName:
Description: Bucket name for other stacks
Value: !Ref DataBucket
Export:
Name: !Sub ${AWS::StackName}-BucketName
BucketArn:
Description: Bucket ARN for other stacks
Value: !GetAtt DataBucket.Arn
Export:
Name: !Sub ${AWS::StackName}-BucketArn
BucketRegion:
Description: Bucket region
Value: !Ref AWS::Region
Export:
Name: !Sub ${AWS::StackName}-BucketRegion
Importing Values in Another Stack
Parameters:
DataBucketName:
Type: AWS::S3::Bucket::Name
Description: Data bucket name from data stack
# User selects from exported values in console
# Or use Fn::ImportValue for programmatic access
Resources:
BucketAccessRole:
Type: AWS::IAM::Role
Properties:
AssumeRolePolicyDocument:
Version: "2012-10-17"
Statement:
- Effect: Allow
Principal:
Service: lambda.amazonaws.com
Action: sts:AssumeRole
Policies:
- PolicyName: S3Access
PolicyDocument:
Statement:
- Effect: Allow
Action:
- s3:GetObject
- s3:PutObject
Resource: !Sub
- ${BucketArn}/*
- BucketArn: !ImportValue data-stack-BucketArn
Cross-Stack Reference Pattern
Create a dedicated data storage stack that exports values:
# storage-stack.yaml
AWSTemplateFormatVersion: 2010-09-09
Description: S3 storage infrastructure stack
Resources:
DataBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Sub ${AWS::StackName}-data
VersioningConfiguration:
Status: Enabled
PublicAccessBlockConfiguration:
BlockPublicAcls: true
BlockPublicPolicy: true
IgnorePublicAcls: true
RestrictPublicBuckets: true
LogBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Sub ${AWS::StackName}-logs
AccessControl: LogDeliveryWrite
Outputs:
DataBucketName:
Value: !Ref DataBucket
Export:
Name: !Sub ${AWS::StackName}-DataBucketName
DataBucketArn:
Value: !GetAtt DataBucket.Arn
Export:
Name: !Sub ${AWS::StackName}-DataBucketArn
LogBucketName:
Value: !Ref LogBucket
Export:
Name: !Sub ${AWS::StackName}-LogBucketName
Application stack imports these values:
# application-stack.yaml
AWSTemplateFormatVersion: 2010-09-09
Description: Application stack that imports from storage
Parameters:
StorageStackName:
Type: String
Description: Name of the storage stack
Default: storage-stack
Resources:
ApplicationBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Sub ${AWS::StackName}-application
CorsConfiguration:
CorsRules:
- AllowedHeaders:
- "*"
AllowedMethods:
- GET
- PUT
- POST
AllowedOrigins:
- !Ref ApplicationDomain
MaxAge: 3600
S3 Bucket Configuration
Bucket with Public Access Block
Resources:
SecureBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: my-secure-bucket
PublicAccessBlockConfiguration:
BlockPublicAcls: true
BlockPublicPolicy: true
IgnorePublicAcls: true
RestrictPublicBuckets: true
Bucket with Versioning
Resources:
VersionedBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: my-versioned-bucket
VersioningConfiguration:
Status: Enabled
# Use MFADelete to require MFA for version deletion
# MFADelete: Enabled # Optional, requires MFA
Bucket with Lifecycle Rules
Resources:
LifecycleBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: my-lifecycle-bucket
LifecycleConfiguration:
Rules:
# Expire objects after 30 days
- Id: ExpireOldObjects
Status: Enabled
ExpirationInDays: 30
NoncurrentVersionExpirationInDays: 7
# Archive to Glacier after 90 days
- Id: ArchiveToGlacier
Status: Enabled
Transitions:
- Days: 90
StorageClass: GLACIER
- Days: 365
StorageClass: DEEP_ARCHIVE
NoncurrentVersionTransitions:
- NoncurrentDays: 30
StorageClass: GLACIER
Bucket with Cross-Region Replication
Resources:
SourceBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: my-source-bucket
VersioningConfiguration:
Status: Enabled
ReplicationConfiguration:
Role: !GetAtt ReplicationRole.Arn
Rules:
- Id: ReplicateToDestRegion
Status: Enabled
Destination:
Bucket: !Sub arn:aws:s3:::my-dest-bucket-${AWS::Region}
StorageClass: STANDARD_IA
EncryptionConfiguration:
ReplicaKmsKeyID: !Ref DestKMSKey
ReplicationRole:
Type: AWS::IAM::Role
Properties:
AssumeRolePolicyDocument:
Version: "2012-10-17"
Statement:
- Effect: Allow
Principal:
Service: s3.amazonaws.com
Action: sts:AssumeRole
Bucket Policies
Bucket Policy for Private Access
Resources:
PrivateBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: my-private-bucket
PublicAccessBlockConfiguration:
BlockPublicAcls: true
BlockPublicPolicy: true
IgnorePublicAcls: true
RestrictPublicBuckets: true
BucketPolicy:
Type: AWS::S3::BucketPolicy
Properties:
Bucket: !Ref PrivateBucket
PolicyDocument:
Statement:
- Sid: DenyPublicRead
Effect: Deny
Principal: "*"
Action:
- s3:GetObject
Resource: !Sub ${PrivateBucket.Arn}/*
Condition:
Bool:
aws:SecureTransport: false
Bucket Policy for CloudFront OAI
Resources:
StaticWebsiteBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: my-static-website
WebsiteConfiguration:
IndexDocument: index.html
ErrorDocument: error.html
BucketPolicy:
Type: AWS::S3::BucketPolicy
Properties:
Bucket: !Ref StaticWebsiteBucket
PolicyDocument:
Statement:
- Sid: CloudFrontReadAccess
Effect: Allow
Principal:
CanonicalUser: !GetAtt CloudFrontOAI.S3CanonicalUserId
Action: s3:GetObject
Resource: !Sub ${StaticWebsiteBucket.Arn}/*
CloudFrontOAI:
Type: AWS::CloudFront::CloudFrontOriginAccessIdentity
Properties:
CloudFrontOriginAccessIdentityConfig:
Comment: !Sub ${AWS::StackName}-oai
Bucket Policy for VPC Endpoint
Resources:
PrivateBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: my-private-bucket
BucketPolicy:
Type: AWS::S3::BucketPolicy
Properties:
Bucket: !Ref PrivateBucket
PolicyDocument:
Statement:
- Sid: AllowVPCEndpoint
Effect: Allow
Principal: "*"
Action: s3:GetObject
Resource: !Sub ${PrivateBucket.Arn}/*
Condition:
StringEquals:
aws:sourceVpce: !Ref VPCEndpointId
Complete S3 Bucket Example
AWSTemplateFormatVersion: 2010-09-09
Description: Production-ready S3 bucket with versioning, logging, and lifecycle
Parameters:
BucketName:
Type: String
Description: Name of the S3 bucket
Environment:
Type: String
Default: production
AllowedValues:
- development
- staging
- production
EnableVersioning:
Type: String
Default: true
AllowedValues:
- true
- false
RetentionDays:
Type: Number
Default: 90
Description: Days to retain objects
Conditions:
ShouldEnableVersioning: !Equals [!Ref EnableVersioning, true]
IsProduction: !Equals [!Ref Environment, production]
Resources:
DataBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Ref BucketName
VersioningConfiguration:
Status: !If [ShouldEnableVersioning, Enabled, Suspended]
PublicAccessBlockConfiguration:
BlockPublicAcls: true
BlockPublicPolicy: true
IgnorePublicAcls: true
RestrictPublicBuckets: true
LoggingConfiguration:
DestinationBucketName: !Ref AccessLogBucket
LogFilePrefix: !Sub ${BucketName}/logs/
LifecycleConfiguration:
Rules:
- Id: StandardLifecycle
Status: Enabled
ExpirationInDays: !Ref RetentionDays
NoncurrentVersionExpirationInDays: 30
Transitions:
- Days: 30
StorageClass: STANDARD_IA
- Days: 90
StorageClass: GLACIER
Tags:
- Key: Environment
Value: !Ref Environment
- Key: Name
Value: !Ref BucketName
AccessLogBucket:
Type: AWS::S3::Bucket
Properties:
BucketName: !Sub ${BucketName}-logs
AccessControl: LogDeliveryWrite
PublicAccessBlockConfiguration:
BlockPublicAcls: true
BlockPublicPolicy: true
IgnorePublicAcls: true
RestrictPublicBuckets: true
LifecycleConfiguration:
Rules:
- Id: DeleteLogsAfter30Days
Status: Enabled
ExpirationInDays: 30
Outputs:
BucketName:
Description: Name of the S3 bucket
Value: !Ref DataBucket
BucketArn:
Description: ARN of the S3 bucket
Value: !GetAtt DataBucket.Arn
BucketDomainName:
Description: Domain name of the S3 bucket
Value: !GetAtt DataBucket.DomainName
BucketWebsiteURL:
Description: Website URL for the S3 bucket
Value: !GetAtt DataBucket.WebsiteURL
LogBucketName:
Description: Name of the access log bucket
Value: !Ref AccessLogBucket
CloudFormation Best Practices
Stack Policies
Stack Policies protect stack resources from unintentional updates that could cause disruption or data loss. Use them to prevent accidental modifications to critical resources.
Setting a Stack Policy
{
"Statement": [
{
"Effect": "Allow",
"Action": "Update:*",
"Principal": "*",
"Resource": "*"
},
{
"Effect": "Deny",
"Action": [
"Update:Replace",
"Update:Delete"
],
"Principal": "*",
"Resource": "LogicalResourceId/DataBucket"
},
{
"Effect": "Deny",
"Action": "Update:*",
"Principal": "*",
"Resource": "LogicalResourceId/AccessLogBucket",
"Condition": {
"StringEquals": {
"ResourceType": ["AWS::S3::Bucket"]
}
}
}
]
}
Applying Stack Policy via AWS CLI
aws cloudformation set-stack-policy \
--stack-name my-s3-stack \
--stack-policy-body file://stack-policy.json
Stack Policy for Production Environment
{
"Statement": [
{
"Effect": "Allow",
"Action": ["Update:Modify", "Update:Replace", "Update:Delete"],
"Principal": "*",
"Resource": "*",
"Condition": {
"StringEquals": {
"ResourceType": ["AWS::S3::Bucket"]
}
}
},
{
"Effect": "Deny",
"Action": "Update:Delete",
"Principal": "*",
"Resource": "*"
},
{
"Effect": "Allow",
"Action": "Update:*",
"Principal": "AWS": ["arn:aws:iam::123456789012:role/AdminRole"],
"Resource": "*"
}
]
}
Termination Protection
Termination Protection prevents accidental deletion of CloudFormation stacks. Always enable it for production stacks.
Enabling Termination Protection
# Enable termination protection when creating a stack
aws cloudformation create-stack \
--stack-name my-s3-stack \
--template-body file://template.yaml \
--enable-termination-protection
# Enable termination protection on existing stack
aws cloudformation update-termination-protection \
--stack-name my-s3-stack \
--enable-termination-protection
# Disable termination protection
aws cloudformation update-termination-protection \
--stack-name my-s3-stack \
--no-enable-termination-protection
Termination Protection in SDK (Python)
import boto3
def enable_termination_protection(stack_name):
cfn = boto3.client('cloudformation')
try:
cfn.update_termination_protection(
StackName=stack_name,
EnableTerminationProtection=True
)
print(f"Termination protection enabled for stack: {stack_name}")
except cfn.exceptions.TerminationProtectionError as e:
if "already" in str(e).lower():
print(f"Termination protection already enabled for stack: {stack_name}")
else:
raise
Verification Script
#!/bin/bash
# verify-termination-protection.sh
STACK_NAME=$1
if [ -z "$STACK_NAME" ]; then
echo "Usage: $0 <stack-name>"
exit 1
fi
STATUS=$(aws cloudformation describe-stacks \
--stack-name $STACK_NAME \
--query 'Stacks[0].TerminationProtection' \
--output text)
if [ "$STATUS" = "True" ]; then
echo "Termination protection is ENABLED for $STACK_NAME"
exit 0
else
echo "WARNING: Termination protection is DISABLED for $STACK_NAME"
exit 1
fi
Drift Detection
Drift Detection identifies differences between the actual infrastructure and the CloudFormation template. Run it regularly to ensure compliance.
Detecting Drift
# Detect drift on a single stack
aws cloudformation detect-drift \
--stack-name my-s3-stack
# Detect drift and get detailed results
STACK_NAME="my-s3-stack"
# Start drift detection
aws cloudformation detect-drift \
--stack-name $STACK_NAME
# Wait for drift detection to complete
aws cloudformation wait stack-drift-detection-complete \
--stack-name $STACK_NAME
# Get drift detection status
STATUS=$(aws cloudformation describe-stack-drift-detection-status \
--stack-name $STACK_NAME \
--query 'StackDriftStatus' \
--output text)
echo "Stack drift status: $STATUS"
# Get detailed drift information
if [ "$STATUS" = "DRIFTED" ]; then
aws cloudformation describe-stack-resource-drifts \
--stack-name $STACK_NAME \
--query 'StackResourceDrifts[*].[LogicalResourceId,ResourceType,DriftStatus,PropertyDifferences]' \
--output table
fi
Drift Detection Script with Reporting
#!/bin/bash
# detect-drift.sh
STACK_NAME=$1
REPORT_FILE="drift-report-${STACK_NAME}-$(date +%Y%m%d).json"
if [ -z "$STACK_NAME" ]; then
echo "Usage: $0 <stack-name> [report-file]"
exit 1
fi
if [ -n "$2" ]; then
REPORT_FILE=$2
fi
echo "Starting drift detection for stack: $STACK_NAME"
# Start drift detection
DETECTION_ID=$(aws cloudformation detect-drift \
--stack-name $STACK_NAME \
--query 'Id' \
--output text)
echo "Drift detection initiated. Detection ID: $DETECTION_ID"
# Wait for completion
echo "Waiting for drift detection to complete..."
aws cloudformation wait stack-drift-detection-complete \
--stack-name $STACK_NAME 2>/dev/null || true
# Get detection status
DRIFT_STATUS=$(aws cloudformation describe-stack-drift-detection-status \
--stack-name $STACK_NAME \
--query 'StackDriftStatus' \
--output text 2>/dev/null)
echo "Drift status: $DRIFT_STATUS"
# Get detailed results
if [ "$DRIFT_STATUS" = "DRIFTED" ]; then
echo "Resources with drift detected:"
aws cloudformation describe-stack-resource-drifts \
--stack-name $STACK_NAME \
--output json > "$REPORT_FILE"
echo "Drift report saved to: $REPORT_FILE"
# Display summary
aws cloudformation describe-stack-resource-drifts \
--stack-name $STACK_NAME \
--query 'StackResourceDrifts[?DriftStatus==`MODIFIED`].[LogicalResourceId,ResourceType,PropertyDifferences[].PropertyName]' \
--output table
else
echo "No drift detected. Stack is in sync with template."
echo "{}" > "$REPORT_FILE"
fi
Drift Detection for Multiple Stacks
import boto3
from datetime import datetime
def detect_drift_all_stacks(prefix="prod-"):
cfn = boto3.client('cloudformation')
s3 = boto3.client('s3')
# List all stacks with prefix
stacks = cfn.list_stacks(
StackStatusFilter=['CREATE_COMPLETE', 'UPDATE_COMPLETE']
)['StackSummaries']
target_stacks = [s for s in stacks if s['StackName'].startswith(prefix)]
drift_results = []
for stack in target_stacks:
stack_name = stack['StackName']
print(f"Checking drift for: {stack_name}")
# Start drift detection
response = cfn.detect_drift(StackName=stack_name)
detection_id = response['Id']
# Wait for completion (simplified - in production use waiter)
waiter = cfn.get_waiter('stack_drift_detection_complete')
waiter.wait(StackName=stack_name)
# Get status
status = cfn.describe_stack_drift_detection_status(
StackName=stack_name
)
drift_results.append({
'stack_name': stack_name,
'drift_status': status['StackDriftStatus'],
'detection_time': datetime.utcnow().isoformat()
})
if status['StackDriftStatus'] == 'DRIFTED':
# Get detailed drift info
resources = cfn.describe_stack_resource_drifts(
StackName=stack_name
)['StackResourceDrifts']
drift_results[-1]['drifted_resources'] = [
{
'logical_id': r['LogicalResourceId'],
'type': r['ResourceType'],
'status': r['DriftStatus']
} for r in resources
]
return drift_results
Change Sets
Change Sets preview changes before applying them. Always use them for production deployments to review impact.
Creating and Executing a Change Set
#!/bin/bash
# deploy-with-changeset.sh
STACK_NAME=$1
TEMPLATE_FILE=$2
CHANGESET_NAME="${STACK_NAME}-changeset-$(date +%Y%m%d%H%M%S)"
if [ -z "$STACK_NAME" ] || [ -z "$TEMPLATE_FILE" ]; then
echo "Usage: $0 <stack-name> <template-file>"
exit 1
fi
echo "Creating change set for stack: $STACK_NAME"
# Create change set
aws cloudformation create-change-set \
--stack-name $STACK_NAME \
--template-body file://$TEMPLATE_FILE \
--change-set-name $CHANGESET_NAME \
--capabilities CAPABILITY_IAM \
--change-set-type UPDATE
echo "Change set created: $CHANGESET_NAME"
# Wait for change set creation
aws cloudformation wait change-set-create-complete \
--stack-name $STACK_NAME \
--change-set-name $CHANGESET_NAME
# Display changes
echo ""
echo "=== Change Set Summary ==="
aws cloudformation describe-change-set \
--stack-name $STACK_NAME \
--change-set-name $CHANGESET_NAME \
--query '[ChangeSetName,Status,ChangeSetStatus,StatusReason]' \
--output table
echo ""
echo "=== Detailed Changes ==="
aws cloudformation list-change-sets \
--stack-name $STACK_NAME \
--query "Summaries[?ChangeSetName=='$CHANGESET_NAME'].[Changes]" \
--output text | python3 -m json.tool 2>/dev/null || \
aws cloudformation describe-change-set \
--stack-name $STACK_NAME \
--change-set-name $CHANGESET_NAME \
--query 'Changes[*].ResourceChange' \
--output table
# Prompt for execution
echo ""
read -p "Execute this change set? (yes/no): " CONFIRM
if [ "$CONFIRM" = "yes" ]; then
echo "Executing change set..."
aws cloudformation execute-change-set \
--stack-name $STACK_NAME \
--change-set-name $CHANGESET_NAME
echo "Waiting for stack update to complete..."
aws cloudformation wait stack-update-complete \
--stack-name $STACK_NAME
echo "Stack update complete!"
else
echo "Change set execution cancelled."
echo "To execute later, run:"
echo "aws cloudformation execute-change-set --stack-name $STACK_NAME --change-set-name $CHANGESET_NAME"
fi
Change Set with Parameter Overrides
# Create change set with parameters
aws cloudformation create-change-set \
--stack-name my-s3-stack \
--template-body file://template.yaml \
--change-set-name my-changeset \
--parameters \
ParameterKey=BucketName,ParameterValue=my-new-bucket \
ParameterKey=Environment,ParameterValue=production \
--capabilities CAPABILITY_IAM
# Generate change set from existing stack
aws cloudformation create-change-set \
--stack-name my-s3-stack \
--template-body file://new-template.yaml \
--change-set-name migrate-to-new-template \
--change-set-type IMPORT \
--resources-to-import "[\"DataBucket\", \"AccessLogBucket\"]"
Change Set Preview Script
import boto3
def preview_changes(stack_name, template_body, parameters=None):
cfn = boto3.client('cloudformation')
changeset_name = f"{stack_name}-preview-{int(__import__('time').time())}"
try:
# Create change set
kwargs = {
'StackName': stack_name,
'TemplateBody': template_body,
'ChangeSetName': changeset_name,
'ChangeSetType': 'UPDATE'
}
if parameters:
kwargs['Parameters'] = parameters
response = cfn.create_change_set(**kwargs)
# Wait for creation
waiter = cfn.get_waiter('change_set_create_complete')
waiter.wait(StackName=stack_name, ChangeSetName=changeset_name)
# Get change set description
changeset = cfn.describe_change_set(
StackName=stack_name,
ChangeSetName=changeset_name
)
print(f"Change Set: {changeset['ChangeSetName']}")
print(f"Status: {changeset['Status']}")
print(f"Number of changes: {len(changeset.get('Changes', []))}")
# Display each change
for change in changeset.get('Changes', []):
resource = change['ResourceChange']
print(f"\n{resource['Action']} {resource['LogicalResourceId']} ({resource['ResourceType']})")
if resource.get('Replacement') == 'True':
print(f" - This resource will be REPLACED (potential downtime)")
for detail in resource.get('Details', []):
print(f" - {detail['Attribute']}: {detail['Name']}")
return changeset
except cfn.exceptions.AlreadyExistsException:
print(f"Change set already exists")
return None
finally:
# Clean up change set
try:
cfn.delete_change_set(
StackName=stack_name,
ChangeSetName=changeset_name
)
except Exception:
pass
Change Set Best Practices
# Best practices for change sets
# 1. Always use descriptive change set names
CHANGESET_NAME="update-bucket-config-$(date +%Y%m%d)"
# 2. Use appropriate change set type
aws cloudformation create-change-set \
--stack-name my-stack \
--change-set-type UPDATE \
--template-body file://template.yaml
# 3. Review changes before execution
aws cloudformation describe-change-set \
--stack-name my-stack \
--change-set-name $CHANGESET_NAME \
--query 'Changes[].ResourceChange'
# 4. Use capabilities flag when needed
aws cloudformation create-change-set \
--stack-name my-stack \
--capabilities CAPABILITY_IAM CAPABILITY_NAMED_IAM \
--template-body file://template.yaml
# 5. Set execution role for controlled deployments
aws cloudformation create-change-set \
--stack-name my-stack \
--execution-role-name arn:aws:iam::123456789012:role/CloudFormationExecutionRole \
--template-body file://template.yaml
Related Files
For detailed resource reference information, see:
- reference.md - Complete AWS::S3::Bucket and AWS::S3::BucketPolicy properties
For comprehensive examples, see:
- examples.md - Real-world S3 patterns and use cases