Azure Application Gateway Documentation

Understanding Azure Application Gateway

Azure Application Gateway is a scalable, fully managed web traffic load balancer that enables you to manage traffic to your web applications. It provides Layer 7 load balancing capabilities, allowing for content-based routing, cookie-based session affinity, SSL termination, and more. Application Gateway can be used to direct traffic based on URL path, host name, and other route-based rules.

This service is ideal for applications requiring sophisticated routing rules, high availability, and enhanced security features. It acts as a reverse proxy, sitting in front of your backend servers and handling incoming requests.

Key Features

Web Application Firewall (WAF): Protects your web applications from common web exploits and vulnerabilities such as SQL injection, cross-site scripting (XSS), and cross-site forgery (CSRF).
SSL Termination: Offloads SSL/TLS decryption from your web servers, simplifying management and improving performance.
Cookie-Based Session Affinity: Ensures that requests from a specific client are always routed to the same backend server.
Content-Based Routing: Routes traffic to different backend pools based on URL path, HTTP headers, or host names.
Health Probes: Continuously monitors the health of your backend servers and routes traffic only to healthy instances.
Autoscaling: Automatically adjusts capacity based on traffic load.
Virtual Network Integration: Can be deployed within your Azure Virtual Network.
Rewrite HTTP Headers: Allows for modification of request and response headers.

Common Usage Scenarios

Load Balancing Web Applications: Distributing incoming HTTP/HTTPS traffic across multiple instances of your web applications.
Microservices Routing: Directing requests to specific microservices based on the request path.
Securing Applications: Implementing a WAF to protect against common web attacks.
DevOps Environments: Routing traffic to different deployment slots or versions of an application.
High Availability and Disaster Recovery: Ensuring application availability by distributing traffic across multiple instances and regions.

Basic Configuration Steps

Configuring Azure Application Gateway typically involves the following steps:

Create an Application Gateway: Define its size, SKU, and backend pool.
Configure a Listener: Specify the frontend IP address, port, protocol (HTTP/HTTPS), and SSL certificate if applicable.
Define Routing Rules: Map listeners to backend pools and specify path-based or host-based routing rules.
Configure Backend Pools: List the IP addresses or FQDNs of your backend servers.
Set up Health Probes: Define how the gateway should check the health of your backend servers.

Here's a simplified conceptual example of a routing rule:


Microsoft.Network/applicationGateways
myAppGateway

  
    Standard_v2
    Standard_v2
  
  ...
  ...
  
    
      myHttpListener
      
        ...
        80
        Http
      
    
  
  
    
      myRoutingRule
      
        ...myHttpListener...
        ...myBackendPool...
        ...myBackendHttpSettings...
      
    
  
  ...

Note: This is a simplified representation. Actual ARM templates or Azure CLI/PowerShell commands will be more detailed.

Monitoring Application Gateway

Effective monitoring is crucial for ensuring the health and performance of your applications. Azure Application Gateway integrates with Azure Monitor for comprehensive insights.

Metrics: Track performance metrics such as request count, latency, unhealthy host counts, and WAF rule hits.
Diagnostic Logs: Collect detailed logs for requests, WAF events, and gateway performance.
Application Gateway Health: Utilize the built-in health probes to identify and diagnose issues with backend servers.
Alerting: Configure alerts based on specific metrics or log events to be notified of potential problems.

Pricing Information

Azure Application Gateway pricing is based on the SKU (e.g., Standard_v2, WAF_v2) you choose, the number of instances running, and data processed. Features like WAF and autoscaling also influence the cost. For the most accurate and up-to-date pricing, please refer to the official Azure Application Gateway pricing page.