Azure Application Gateway SSL Configuration

This document provides a comprehensive guide to configuring SSL (Secure Sockets Layer) and TLS (Transport Layer Security) certificates with Azure Application Gateway. Securely encrypting traffic between clients and your applications is crucial for protecting sensitive data and ensuring compliance.

SSL Offloading

SSL offloading is a common scenario where Application Gateway terminates the SSL connection from the client. This means the encrypted traffic from the client is decrypted by Application Gateway, and then forwarded as unencrypted HTTP traffic to the backend servers. This reduces the CPU load on your backend servers, as they don't need to handle SSL decryption.

To enable SSL offloading, you need to upload an SSL certificate to Application Gateway and configure a listener for HTTPS traffic. The certificate must be in a .pfx file format and protected by a private key.

End-to-End SSL Encryption

For enhanced security, you can configure Application Gateway to perform end-to-end SSL encryption. In this scenario, Application Gateway decrypts the SSL traffic from the client, then re-encrypts it before forwarding it to the backend server. This requires configuring SSL certificates on your backend servers as well.

End-to-end SSL ensures that traffic remains encrypted throughout its journey from the client to the backend application. This is particularly important for applications handling highly sensitive data.

Certificate Management

Managing your SSL certificates is a critical part of maintaining secure and reliable operations. Application Gateway supports two primary methods for managing certificates:

PFX Files

You can upload SSL certificates directly to Application Gateway in .pfx (PKCS #12) format. This file contains the certificate and its corresponding private key, typically protected by a password.

When uploading a PFX file, you will be prompted for the password to extract the private key.

# Example using Azure CLI to upload a PFX certificate
az network application-gateway ssl-cert create --gateway-name MyGateway \
  --name MySSLCert --resource-group MyResourceGroup \
  --cert-file "C:\path\to\your\certificate.pfx" \
  --password "your_certificate_password"
            

Azure Key Vault Integration

For enhanced security and streamlined management, you can integrate Application Gateway with Azure Key Vault. This allows you to store your SSL certificates securely in Key Vault and grant Application Gateway access to retrieve them.

Key benefits of using Key Vault:

• Centralized certificate management
• Automated certificate renewal (when configured in Key Vault)
• Improved security by keeping private keys out of your local environment

To integrate with Key Vault, you need to:

1. Store your certificate in Azure Key Vault.
2. Grant Application Gateway's managed identity (or a service principal) permissions to retrieve certificates from the Key Vault.
3. Configure Application Gateway to reference the certificate from Key Vault.

# Example of referencing a Key Vault certificate (conceptually)
# In the Azure portal or via ARM/Bicep templates, you specify Key Vault details.
# This is not a direct CLI command for a single step, but represents the configuration.

# Application Gateway configuration snippet (simplified):
{
  "type": "Microsoft.Network/applicationGateways/sslCertificates",
  "name": "myKeyVaultCert",
  "properties": {
    "keyVaultSecretId": "/subscriptions/.../resourceGroups/.../providers/Microsoft.KeyVault/vaults/.../secrets/myCertName/versions/..."
  }
}
            

Configuring SSL Settings

SSL settings are configured at the listener level within Application Gateway. You can specify:

• The SSL certificate to use for the listener.
• The SSL protocol versions to support (e.g., TLSv1.2, TLSv1.3).
• The cipher suites to enable or disable.
• Whether to use Server Name Indication (SNI) for hosting multiple SSL certificates on the same IP address.

Best Practices

• Always use the latest supported TLS versions (e.g., TLS 1.2 or TLS 1.3).
• Use strong cipher suites and disable weak ones.
• Regularly update and rotate your SSL certificates.
• Leverage Azure Key Vault for secure and efficient certificate management.
• Enable SSL offloading or end-to-end SSL based on your security requirements.
• Configure HSTS (HTTP Strict Transport Security) headers to enforce HTTPS connections.
• Monitor your SSL certificate expiration dates to prevent service interruptions.

By correctly configuring SSL settings on Azure Application Gateway, you can significantly enhance the security posture of your web applications and protect your users' data.