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feature-flags.md

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Feature Flags

Cost optimization and feature toggles for AWS Static Website Infrastructure deployment.

Overview

Feature flags allow conditional resource deployment based on environment requirements, enabling cost optimization while maintaining functionality where needed.

Note: The environment configuration examples in this document are illustrative, showing recommended patterns for fork users. Actual environment files (terraform/environments/*/main.tf) currently use module defaults without explicit overrides. Adjust these examples to match your requirements.

Available Feature Flags

CloudFront CDN

variable "enable_cloudfront" {
  description = "Enable CloudFront CDN distribution"
  type        = bool
  default     = false
}

Impact:

  • ✅ Enabled: Global CDN, improved performance, ~$15-25/month additional cost
  • ❌ Disabled (default): Direct S3 access, regional performance, cost-optimized

WAF Protection

variable "enable_waf" {
  description = "Enable AWS WAF v2 protection"
  type        = bool
  default     = false
}

Impact:

  • ✅ Enabled: OWASP Top 10 protection, rate limiting, ~$5-10/month additional cost
  • ❌ Disabled (default): Basic S3 security only, cost-optimized

Note: WAF requires CloudFront (enable_cloudfront = true) for S3 static websites, as AWS WAF cannot directly attach to S3 buckets.

Cross-Region Replication

variable "enable_cross_region_replication" {
  description = "Enable S3 cross-region replication to us-west-2"
  type        = bool
  default     = true
}

Impact:

  • ✅ Enabled (default): Disaster recovery, 2x storage costs, bandwidth costs
  • ❌ Disabled: Single-region deployment, standard storage costs

Route 53 DNS

variable "enable_route53" {
  description = "Enable Route 53 DNS management"
  type        = bool
  default     = false
}

Impact:

  • ✅ Enabled: Custom domain support, health checks, ~$0.50/month
  • ❌ Disabled: CloudFront/S3 URLs only, no additional DNS costs

Environment-Specific Configuration

Development Environment

# terraform/environments/dev/main.tf
module "static_website" {
  source = "../../workloads/static-site"

  # Cost-optimized configuration
  enable_cloudfront                = false  # 💰 Save $15-25/month
  enable_waf                      = false  # 💰 Save $5-10/month
  enable_cross_region_replication = false  # 💰 Save storage costs
  enable_route53                  = false  # 💰 Save DNS costs

  # Result: ~$1-5/month total cost
}

Staging Environment

# terraform/environments/staging/main.tf
module "static_website" {
  source = "../../workloads/static-site"

  # Balanced configuration
  enable_cloudfront                = true   # ✅ Performance testing
  enable_waf                      = true   # ✅ Security testing
  enable_cross_region_replication = true   # ✅ DR testing
  enable_route53                  = false  # ❌ Optional for staging

  # Result: ~$15-25/month total cost
}

Production Environment

# terraform/environments/prod/main.tf
module "static_website" {
  source = "../../workloads/static-site"

  # Full-featured configuration
  enable_cloudfront                = true   # ✅ Global performance
  enable_waf                      = true   # ✅ Security protection
  enable_cross_region_replication = true   # ✅ Disaster recovery
  enable_route53                  = true   # ✅ Custom domain

  # Result: ~$25-50/month total cost
}

Cost Impact Analysis

Cost Breakdown by Feature

Feature Default Development Staging Production Annual Impact
Base S3 Always $1-2 $3-5 $5-10 $108-204
CloudFront ❌ Disabled ❌ $0 ✅ $10-15 ✅ $15-25 $300-480
WAF ❌ Disabled ❌ $0 ✅ $5-8 ✅ $8-12 $156-240
Replication ✅ Enabled ✅ $2-4 ✅ $2-5 ✅ $3-8 $84-204
Route 53 ❌ Disabled ❌ $0 ❌ $0 ✅ $0.50 $6
Total/Month - $3-6 $20-33 $31-55 $648-1134

Optimization Strategies

Cost-First Approach

  • Start with development configuration
  • Enable features only when needed
  • Monitor actual usage patterns
  • Scale up based on requirements

Performance-First Approach

  • Enable all features in staging
  • Test performance impact
  • Optimize based on metrics
  • Full production deployment

Feature Flag Management

Toggling Features

Via OpenTofu/Terraform Variables

# Disable CloudFront in development
cd terraform/environments/dev
echo 'enable_cloudfront = false' >> terraform.tfvars

Via Environment Variables

# GitHub Actions workflow
TF_VAR_enable_cloudfront=false gh workflow run run.yml

Validation

Each feature flag includes validation logic to ensure consistent configuration:

# Example validation
variable "enable_waf" {
  type    = bool
  default = true

  validation {
    condition     = var.enable_cloudfront == true || var.enable_waf == false
    error_message = "WAF requires CloudFront to be enabled."
  }
}

Monitoring Feature Usage

CloudWatch Metrics

Track feature utilization and cost impact:

# CloudFront usage (if enabled)
aws cloudwatch get-metric-statistics \
  --namespace AWS/CloudFront \
  --metric-name Requests \
  --start-time 2025-09-01T00:00:00Z \
  --end-time 2025-09-22T00:00:00Z \
  --period 3600 \
  --statistics Sum

# WAF blocked requests (if enabled)
aws cloudwatch get-metric-statistics \
  --namespace AWS/WAFV2 \
  --metric-name BlockedRequests \
  --start-time 2025-09-01T00:00:00Z \
  --end-time 2025-09-22T00:00:00Z \
  --period 3600 \
  --statistics Sum

Cost Analysis

# Get cost breakdown by service
aws ce get-cost-and-usage \
  --time-period Start=2025-09-01,End=2025-09-22 \
  --granularity MONTHLY \
  --metrics BlendedCost \
  --group-by Type=DIMENSION,Key=SERVICE

Best Practices

1. Environment-Appropriate Configuration

  • Development: Minimal features, maximum cost savings
  • Staging: Mirror production features for accurate testing
  • Production: Full features based on actual requirements

2. Gradual Feature Adoption

  • Start with cost-optimized configuration
  • Enable features based on actual needs
  • Monitor impact before permanent adoption

3. Regular Review

  • Monthly cost analysis
  • Quarterly feature utilization review
  • Annual architecture optimization

4. Documentation

  • Document feature decisions and rationale
  • Track cost impact over time
  • Share learnings across team

Troubleshooting

Common Issues

CloudFront disabled but expecting CDN behavior

# Check feature flag status
grep enable_cloudfront terraform/environments/*/terraform.tfvars
# Expected: false for development, true for staging/prod

WAF enabled without CloudFront

# This configuration will fail validation
# WAF requires CloudFront to function

Unexpected high costs

# Check which features are enabled
tofu output | grep -E "(cloudfront|waf|replication)"
# Review feature flags in terraform.tfvars

For more cost optimization strategies, see Architecture Guide. For deployment procedures, see Deployment Guide.