While both AWS Site-to-Site VPN and Client VPN serve the purpose of secure connectivity, they operate at different network layers and serve distinct use cases:

• Site-to-Site VPN uses IPSec (Layer 3) to connect entire networks (e.g., corporate office to AWS VPC)
• Client VPN uses TLS (Application Layer) to connect individual devices to AWS resources

The protocol difference leads to several technical implications:

# Site-to-Site VPN configuration example (IPSec)
aws ec2 create-vpn-connection \
    --type ipsec.1 \
    --customer-gateway-id cgw-123456 \
    --vpn-gateway-id vgw-123456 \
    --options "{\"StaticRoutesOnly\":true}"

# Client VPN configuration example (TLS)
aws ec2 create-client-vpn-endpoint \
    --client-cidr-block 10.0.0.0/22 \
    --server-certificate-arn arn:aws:acm:us-east-1:123456789012:certificate/12345678-1234-1234-1234-123456789012 \
    --authentication-options "Type=certificate-authentication,ActiveDirectoryArn=arn:aws:directoryservice:us-east-1:123456789012:directory/d-1234567890" \
    --connection-log-options "Enabled=false" \
    --dns-servers "10.0.0.2" \
    --transport-protocol tcp

Site-to-Site VPN is ideal for:

• Connecting entire corporate networks to AWS
• Hybrid cloud architectures requiring persistent connections
• High-throughput scenarios (supports up to 1.25 Gbps per tunnel)

Client VPN is better suited for:

• Remote worker access to AWS resources
• Temporary access scenarios
• Mobile workforce requirements
• When you need granular access control per user/device

While both options are secure, they have different security models:

# Example: Verifying VPN connection status (Python boto3)
import boto3

def check_vpn_status():
    ec2 = boto3.client('ec2')
    
    # For Site-to-Site VPN
    site_vpns = ec2.describe_vpn_connections()
    print("Site-to-Site VPNs:", site_vpns)
    
    # For Client VPN
    client_vpns = ec2.describe_client_vpn_endpoints()
    print("Client VPNs:", client_vpns)

Metric	Site-to-Site VPN	Client VPN
Maximum Throughput	1.25 Gbps per tunnel	100-200 Mbps per endpoint
Latency	Lower (direct IPSec)	Higher (TLS overhead)
Connection Persistence	Always-on	On-demand

For Site-to-Site VPN:

• Use BGP routing for dynamic path selection
• Implement multiple tunnels for redundancy
• Monitor tunnel status with CloudWatch metrics

For Client VPN:

• Use certificate-based authentication
• Implement proper authorization rules
• Enable connection logging for audit purposes

# Terraform example for both VPN types
resource "aws_vpn_connection" "site_to_site" {
  vpn_gateway_id      = aws_vpn_gateway.vpn_gw.id
  customer_gateway_id = aws_customer_gateway.customer_gw.id
  type                = "ipsec.1"
  static_routes_only  = true
}

resource "aws_ec2_client_vpn_endpoint" "client_vpn" {
  description            = "Client VPN Access"
  server_certificate_arn = aws_acm_certificate.client_cert.arn
  client_cidr_block      = "10.0.0.0/22"
  
  authentication_options {
    type                       = "certificate-authentication"
    root_certificate_chain_arn = aws_acm_certificate.root_cert.arn
  }
  
  connection_log_options {
    enabled = false
  }
}

Site-to-Site VPN pricing is based on:

• Connection hours
• Data transfer out of AWS

Client VPN pricing includes:

• Endpoint association hours
• Active client connections
• Data transfer

Generally, Client VPN has higher operational costs for large-scale deployments due to per-client licensing.

---

At its core, the fundamental distinction lies in the networking layers they operate on:

• Site-to-Site VPN: Establishes IPSec tunnels at Layer 3 (Network Layer) between your on-premises network and AWS VPC. Example configuration in CloudFormation:

Resources:
  VPNConnection:
    Type: AWS::EC2::VPNConnection
    Properties:
      Type: ipsec.1
      CustomerGatewayId: !Ref CustomerGateway
      VpnGatewayId: !Ref VPNGateway
      StaticRoutesOnly: true

• Client VPN: Uses TLS at Layer 7 (Application Layer) for individual device connections. Terraform example for endpoint setup:

resource "aws_ec2_client_vpn_endpoint" "main" {
  server_certificate_arn = aws_acm_certificate.server.arn
  client_cidr_block      = "10.2.0.0/16"
  vpc_id                 = aws_vpc.main.id
  security_group_ids     = [aws_security_group.client_vpn.id]
  authentication_options {
    type              = "certificate-authentication"
    root_certificate_chain_arn = aws_acm_certificate.root.arn
  }
  connection_log_options {
    enabled = false
  }
}

The choice between these VPN types impacts several architectural aspects:

1. Network Topology: Site-to-Site connects entire networks (e.g., branch office to AWS), while Client VPN connects individual devices (developers' laptops)
2. Routing Complexity: Site-to-Site requires BGP or static routing configuration
3. Authentication Methods: Client VPN supports Active Directory integration and certificate-based auth

Based on AWS Performance Lab tests:

Metric	Site-to-Site VPN	Client VPN
Max Throughput	1.25 Gbps	300 Mbps
Connection Setup Time	15-30 seconds	2-5 seconds
Max Connections	50 tunnels per VGW	2000 concurrent users

Choose Site-to-Site VPN when:

• Migrating legacy applications that require layer 3 connectivity
• Needing persistent connections between data centers and AWS
• Requiring compatibility with existing IPSec hardware

Choose Client VPN when:

• Providing secure remote access for distributed teams
• Needing granular user-level access controls
• Working with containerized applications where TLS termination is standard

Both services support encryption, but with different implementations:

# Sample IAM policy for VPN access control
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "ec2:CreateClientVpnEndpoint",
        "ec2:CreateClientVpnRoute"
      ],
      "Resource": "*",
      "Condition": {
        "IpAddress": {"aws:SourceIp": ["203.0.113.0/24"]}
      }
    }
  ]
}

Client VPN provides additional security features like:

• Per-user authentication logging
• Session timeout controls
• Client-side certificate revocation