CloudFront distributions should have a default root object configured to prevent user access errors and reduce unnecessary costs. The default root object is the file that CloudFront returns when users access your distribution’s root URL without specifying a particular file. Without this configuration, users may encounter 403 or 404 errors, leading to poor user experience and potential revenue loss.
Why This Policy Matters
Cost Impact and User Experience
CloudFront distributions without a default root object create several financial and operational challenges:
- Error Response Costs: When users access your root URL without a default object configured, CloudFront may return error responses. These errors still consume bandwidth and generate charges, but provide no value to your users or business.
- Origin Load Increase: Without proper default object configuration, your origin servers may receive more requests as CloudFront attempts to resolve undefined paths, increasing compute and bandwidth costs at the origin level.
- Support and Troubleshooting Overhead: User-reported access issues require engineering time to investigate and resolve, adding operational costs to your infrastructure team.
How It Reduces Costs
Implementing a default root object policy delivers cost savings through several mechanisms:
- Reduced error responses: Eliminates unnecessary bandwidth charges for error pages
- Lower origin requests: Decreases the number of requests hitting your origin infrastructure
- Decreased support tickets: Prevents user-reported access issues that require investigation
- Improved cache efficiency: Enables better caching strategies for your main landing page
Potential Savings Examples
Consider a typical web application receiving 100,000 root URL requests monthly:
Without default root object:
- 100,000 error responses at $0.085 per GB (US/EU) = ~$8.50/month in wasted bandwidth
- Additional origin requests for error handling = ~$5-15/month depending on origin type
- Engineering time for troubleshooting = 2-4 hours monthly ($200-400 in opportunity cost)
Total monthly waste: $213-423 per 100,000 requests
With default root object:
- Proper content delivery with efficient caching
- Reduced origin load
- Zero error-related support overhead
For organizations with multiple distributions or higher traffic volumes, these savings scale significantly.
Implementation Guide
Infrastructure-as-Code Example
Here’s how to properly configure a default root object in Terraform:
Problematic Configuration:
resource "aws_cloudfront_distribution" "example" {
origin {
domain_name = "example.com"
origin_id = "example-origin"
custom_origin_config {
http_port = 80
https_port = 443
origin_protocol_policy = "https-only"
origin_ssl_protocols = ["TLSv1.2"]
}
}
default_cache_behavior {
target_origin_id = "example-origin"
viewer_protocol_policy = "redirect-to-https"
allowed_methods = ["GET", "HEAD"]
cached_methods = ["GET", "HEAD"]
forwarded_values {
query_string = false
cookies {
forward = "none"
}
}
}
enabled = true
# Missing default_root_object configuration
}Corrected Configuration:
resource "aws_cloudfront_distribution" "example" {
origin {
domain_name = "example.com"
origin_id = "example-origin"
custom_origin_config {
http_port = 80
https_port = 443
origin_protocol_policy = "https-only"
origin_ssl_protocols = ["TLSv1.2"]
}
}
default_cache_behavior {
target_origin_id = "example-origin"
viewer_protocol_policy = "redirect-to-https"
allowed_methods = ["GET", "HEAD"]
cached_methods = ["GET", "HEAD"]
forwarded_values {
query_string = false
cookies {
forward = "none"
}
}
}
enabled = true
default_root_object = "index.html" # Added default root object
restrictions {
geo_restriction {
restriction_type = "none"
}
}
viewer_certificate {
cloudfront_default_certificate = true
}
}Manual Configuration Steps
For existing CloudFront distributions through the AWS Console:
- Navigate to CloudFront Console
- Log into AWS Management Console
- Go to CloudFront service
- Select your distribution
- Edit Distribution Settings
- Click on the distribution ID
- Select the “General” tab
- Click “Edit”
- Configure Default Root Object
- Locate the “Default Root Object” field
- Enter your default file (typically index.html)
- Click “Yes, Edit”
- Wait for Deployment
- Distribution status will show “In Progress”
- Wait for deployment to complete (typically 5-15 minutes)
Best Practices
File Selection:
- Use index.html for static websites
- Use index.php for PHP applications
- Consider default.aspx for .NET applications
- Ensure the file exists at your origin
Testing and Validation:
- Test root URL access after configuration
- Verify caching behavior works as expected
- Monitor CloudWatch metrics for error rate reduction
- Check origin request patterns
Multi-Environment Considerations:
- Use consistent default objects across environments
- Document default root object choices in infrastructure documentation
- Include default root object configuration in CI/CD pipeline templates
Tools and Scripts
This policy is fully supported in Infracost, which enables you to scan your codebase and identify CloudFront distributions missing default root objects. Infracost offers a free trial that allows you to detect these cost optimization opportunities before they impact production workloads. By integrating Infracost into your development workflow, you can prevent these issues from reaching production and systematically address existing instances across your infrastructure.
AWS CLI Script for Bulk Updates:
#!/bin/bash
# Script to check and update CloudFront distributions
aws cloudfront list-distributions --query 'DistributionList.Items[?DefaultRootObject==`null`].[Id,DomainName]' --output table
# Update specific distribution (replace DISTRIBUTION_ID)
aws cloudfront get-distribution-config --id DISTRIBUTION_ID > config.json
# Edit config.json to add DefaultRootObject
aws cloudfront update-distribution --id DISTRIBUTION_ID --distribution-config file://config.json --if-match ETAGConsiderations and Caveats
When This Policy May Not Apply
API-Only Distributions: CloudFront distributions serving only API endpoints may not require default root objects, as they don’t expect root URL access patterns.
Custom Routing Logic: Applications with complex routing mechanisms may handle root requests differently, making default objects unnecessary.
Redirect-Only Distributions: Distributions configured purely for redirects to other domains might not benefit from default root objects.
Potential Drawbacks
File Availability: The specified default root object must exist at your origin. Missing files will still generate 404 errors.
Caching Implications: Default root objects are cached according to your distribution’s caching behavior, which may not align with your application’s requirements for the root path.
SEO Considerations: Ensure your default root object aligns with your SEO strategy and canonical URL structure.
Implementation Challenges
Legacy Applications: Older applications may have different file structures or naming conventions that require careful consideration when selecting default objects.
Multi-Language Sites: Websites supporting multiple languages may need more complex routing logic rather than simple default objects.
Dynamic Content: Applications serving primarily dynamic content may need to carefully consider caching implications of their chosen default object.
Monitoring and Maintenance
Key Metrics to Track
- 4xx error rates before and after implementation
- Origin request patterns to verify reduced load
- Cache hit ratios for root path requests
- User experience metrics like bounce rates from the root URL
Ongoing Maintenance
- Regular audits of new distributions to ensure policy compliance
- Documentation updates when default objects change
- Testing procedures for validating default object functionality
- Monitoring alerts for increases in 4xx errors that might indicate issues