Azure Application Gateway Overview
What Is Azure Application Gateway?
In Azure, an API Gateway is the core component of Azure API Management. It serves as a central hub and a single-entry point for all API requests, acting as a facade for your backend services.
Azure Application Gateway is a web traffic load balancer that operates at the application layer (OSI Layer 7). Unlike traditional load balancers that route traffic based on IP and port, Application Gateway makes routing decisions based on HTTP request attributes such as URL path and host headers. It supports features like SSL termination, URL-based routing, session affinity, and integrated Web Application Firewall (WAF).
Key Features
- Layer 7 Load Balancing: Routes traffic based on HTTP attributes like path and headers.
- SSL Termination: Offloads SSL processing from backend servers.
- Web Application Firewall (WAF): Protects against OWASP Top 10 threats.
- URL-Based Routing: Directs traffic to different backend pools based on URL patterns.
- Session Affinity: Ensures user sessions stick to the same backend server.
- Auto Scaling: Automatically adjusts capacity based on traffic load.
- Custom Probes: Monitors backend health and routes traffic accordingly.
- Private Link Support: Enables secure, private access to backend services.
- Request Routing: It directs incoming API calls to the appropriate backend services, abstracting the complexity of your backend architecture from API consumers.
- Security & Policy Enforcement: It enforces security policies like authentication (e.g., OAuth 2.0, API keys), authorization, rate limiting, and throttling to protect your APIs from misuse and ensure fair usage.
- Traffic Management: It manages and monitors API traffic, enabling features like caching for improved performance, compression of responses, and load balancing.
- API Versioning: It facilitates the management of different API versions, allowing for smooth transitions and backward compatibility.
- Analytics & Monitoring: It collects telemetry data and provides insights into API usage, performance, and potential issues.
- Integration: It integrates seamlessly with other Azure services like Azure Functions, Logic Apps, and Azure Kubernetes Service (AKS), enabling the creation of powerful and flexible API architectures.
Pros
- Advanced Routing: Supports complex routing logic using URL paths and host headers.
- Integrated Security: Built-in WAF and DDoS protection enhance application security.
- SSL Offloading: Reduces backend CPU load by handling encryption at the gateway.
- Scalability: Automatically scales with demand, ensuring high availability.
- Session Affinity: Useful for stateful applications requiring sticky sessions.
- Zero Trust Architecture: Supports private-only deployments with secure backend access.
Cons
- Complex Configuration: Initial setup and rule definitions can be intricate.
- Cost: Higher cost compared to basic load balancers, especially with WAF enabled.
- Limited Protocol Support: Only supports HTTP/HTTPS; not suitable for TCP/UDP traffic.
- Latency: Slightly higher latency due to deep packet inspection and SSL termination.
When to Use Azure Application Gateway
- When you need application-layer (Layer 7) routing based on URL paths or headers.
- When your application requires SSL termination and centralized certificate management.
- When you want to protect your web apps using a built-in WAF.
- When your app needs session affinity for consistent user experience.
- When deploying multi-region or microservices architectures with complex routing needs.
Example Scenario: E-Commerce Web Application
An e-commerce company hosts its web application on Azure. The site includes product pages, a shopping cart, and a payment gateway. They use Azure Application Gateway to:
- Route traffic for
/images to a backend pool optimized for static content.
- Route
/checkout to a secure backend with SSL termination and WAF enabled.
- Maintain session affinity for logged-in users during checkout.
- Scale automatically during peak shopping seasons.
This setup improves performance, enhances security, and ensures a seamless shopping experience for users.
Summary
In essence, the Azure API Gateway provides a managed and scalable solution for publishing, securing, and analyzing your APIs, allowing developers to consume them easily and reliably.
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