graph TB
    subgraph "Primary Region (us-east-1)"
        ALB1[ALB]
        EKS1[EKS Cluster]
        RDS1[(RDS Primary)]
        S3_1[S3 Bucket]
    end
    
    subgraph "DR Region (us-west-2)"
        ALB2[ALB - Standby]
        EKS2[EKS Cluster - Standby]
        RDS2[(RDS Read Replica)]
        S3_2[S3 Replica]
    end
    
    Route53[Route 53<br/>Health Checks] --> ALB1
    Route53 -.->|Failover| ALB2
    RDS1 -->|Async Replication| RDS2
    S3_1 -->|Cross-Region Replication| S3_2

# Primary RDS instance
resource "aws_db_instance" "primary" {
  provider               = aws.primary
  identifier             = "${local.name_prefix}-primary"
  engine                 = "postgres"
  backup_retention_period = 7
  multi_az               = true  # HA within region
}

# Cross-region read replica (can be promoted)
resource "aws_db_instance" "replica" {
  provider             = aws.dr
  identifier           = "${local.name_prefix}-replica"
  replicate_source_db  = aws_db_instance.primary.arn
  
  # Ready to promote on failover
  backup_retention_period = 7
}

# Route 53 health check for automatic failover
resource "aws_route53_health_check" "primary" {
  fqdn              = aws_lb.primary.dns_name
  type              = "HTTPS"
  port              = 443
  failure_threshold = 3
}

// Primary bucket with replication
const primaryBucket = new s3.Bucket(this, 'PrimaryBucket', {
  bucketName: `${props.projectName}-primary-${this.account}`,
  versioned: true,  // Required for replication
  encryption: s3.BucketEncryption.S3_MANAGED,
});

// DR bucket in another region
const drBucket = new s3.Bucket(drStack, 'DrBucket', {
  bucketName: `${props.projectName}-dr-${drStack.account}`,
  versioned: true,
});

// Cross-region replication rule
primaryBucket.addReplicationRule({
  destination: drBucket,
  replicateEncryptedObjects: true,
});

// Route 53 failover routing
const healthCheck = new route53.HealthCheck(this, 'HealthCheck', {
  type: route53.HealthCheckType.HTTPS,
  fqdn: primaryAlb.loadBalancerDnsName,
});

new route53.ARecord(this, 'FailoverRecord', {
  zone: hostedZone,
  recordName: 'app',
  target: route53.RecordTarget.fromAlias(
    new route53targets.LoadBalancerTarget(primaryAlb)
  ),
  setIdentifier: 'primary',
  healthCheck: healthCheck,
});