Implement an Azure application gateway, including selecting a routing method

Here’s a step-by-step guide to implement an Azure Application Gateway, including selecting a routing method.

Prerequisites

Before starting, ensure you have:

• Azure Subscription: Access to an active Azure subscription.

• Resource Group: A logical container for your resources.

• Virtual Network (VNet): Set up a VNet with two subnets:

  • Application Gateway Subnet: Reserved for the gateway.

  • Backend Subnet: Where backend servers (e.g., VMs or App Services) reside.

• SSL Certificate (Optional): For HTTPS listeners.

Create an Azure Application Gateway

a. Navigate to the Azure Portal

1. Go to the Azure Portal.

2. Search for "Application Gateway" in the search bar and click Create.

b. Basic Configuration

1. Subscription: Select your subscription.

2. Resource Group: Use an existing one or create a new one.

3. Name: Provide a unique name for the Application Gateway.

4. Region: Choose the same region as your backend resources.

5. Tier: Select the appropriate tier:

   • Standard_v2: For high-performance and autoscaling.

   • WAF_v2: Adds Web Application Firewall capabilities.

6. Autoscaling: Enable autoscaling or set instance count.

c. Frontend Configuration

1. Choose the Frontend IP type:

   • Public IP: For internet-facing applications.

   • Private IP: For internal-only traffic within the VNet.

2. Assign a new or existing Public IP address.

Configure Routing and Backend

a. Backend Pool

1. Add a Backend Pool by providing the following:

   • Target Type: Select VMs, App Services, IP addresses, or FQDNs.

   • Backend Targets: Add the specific resources (e.g., VM IPs or App Service names).

2. Save the backend pool.

b. HTTP Settings

Configure HTTP settings to define how the gateway communicates with backends:

• Protocol: Choose HTTP or HTTPS.

• Port: Use the backend service's listening port (e.g., 80 or 443).

• Cookie-Based Affinity: Enable if you want session persistence.

• Custom Probe (Optional): Use health probes to monitor backend health.

c. Listener

Add a listener to define how the gateway receives client traffic:

• Listener Name: Unique name for the listener.

• Frontend IP: Select the frontend IP configured earlier.

• Protocol: Choose HTTP or HTTPS.

• SSL Certificate (if HTTPS): Upload a PFX certificate file.

d. Routing Rules

Select the routing method

• Basic Routing: All traffic goes to a single backend pool.

• Path-Based Routing: Direct traffic based on URL paths (e.g., /images → Pool A, /api → Pool B).

• Multi-Site Routing: Route based on domain names (e.g., app1.contoso.com and app2.contoso.com).

Create a rule

• Associate the listener with a backend pool and HTTP settings.

• Add specific path mappings or domains if using advanced routing.

Configure Additional Features

a. Enable WAF (Optional)

If using the WAF_v2 tier, configure the Web Application Firewall:

• Select Detection or Prevention Mode.

• Add custom or default WAF rules (e.g., OWASP CRS).

b. HTTP to HTTPS Redirection

• Add a separate listener for HTTP.

• Configure a redirect rule to forward HTTP traffic to the HTTPS listener.

c. SSL Termination

• SSL traffic terminates at the Application Gateway, decrypting traffic before forwarding it to backend servers.

• To maintain encryption, configure HTTPS communication with backend servers.

Review and Create

1. Review all configurations.

2. Click Create to deploy the Application Gateway. Deployment typically takes a few minutes.

Test and Monitor

a. Access the Application

1. Use the Application Gateway's public IP or DNS name to access the application.

2. Verify that traffic is routed correctly.

b. Monitor Performance

1. Use Azure Monitor and Logs to track:

   • Request count.

   • Latency.

   • Backend health status.

2. Set up alerts for specific metrics (e.g., high response times or unhealthy backends).

Routing Example

Scenario: Path-Based Routing

1. URL /images → Backend Pool A (handles image requests).

2. URL /api → Backend Pool B (API services).

Steps:

1. In Routing Rules, choose Path-Based Routing.

2. Add path mappings:

   • /images/* → Pool A.

   • /api/* → Pool B.

3. Save and deploy.

Summary

Let me know if you need commands for deployment via Azure CLI, or ARM templates for automation.