As I started deploying more applications in Azure, I realized that simply spinning up virtual machines or web apps wasn’t enough. To ensure high availability, fault tolerance, and optimized traffic routing, I had to use Azure’s load balancing solutions—specifically, Azure Load Balancer and Azure Application Gateway.
In this blog, I’ll explain how I used these tools to build resilient and scalable architectures, what the differences are, and how to decide which one to use.
✅ What You’ll Learn:
- What is Azure Load Balancer?
- What is Azure Application Gateway?
- Key differences between them
- When and how I used each in my projects
- Basic setup examples and tips
🌐 What is Azure Load Balancer?
Azure Load Balancer is a Layer 4 (TCP/UDP) load balancer that distributes incoming network traffic across multiple virtual machines or instances.
I use it when I need to:
- Distribute traffic evenly to backend VMs
- Set up high availability for internal or internet-facing services
- Support protocols like HTTP, HTTPS, RDP, or custom ports
Types of Load Balancer:
- Public Load Balancer: For internet-facing services
- Internal Load Balancer (ILB): For private traffic inside a VNet
🔧 Example: My Use Case for Azure Load Balancer
I deployed two Windows VMs (VM1, VM2) in an availability set for a test web app. I created:
- A Public Load Balancer
- Health Probes on port 80 (HTTP)
- Load Balancing Rules to distribute traffic to both VMs
This ensured that if one VM went down, traffic was redirected automatically to the healthy one.
🚪 What is Azure Application Gateway?
Azure Application Gateway is a Layer 7 (HTTP/HTTPS) load balancer that works with web traffic. It provides features like:
- URL-based routing
- SSL termination
- Web Application Firewall (WAF)
- Session affinity (cookie-based routing)
I use App Gateway when I need smart routing and web protection for my applications.
🧠 App Gateway Use Case From My Setup
In one of my projects, I hosted two web apps under the same domain:
mydomain.com/app1mydomain.com/app2
I used Azure Application Gateway to:
- Terminate SSL at the gateway
- Route
/app1to Web App 1 - Route
/app2to Web App 2 - Enable WAF to block malicious requests
This setup gave me both flexibility and enhanced security without changing backend apps.
🔍 Load Balancer vs Application Gateway: Key Differences
| Feature | Azure Load Balancer | Azure Application Gateway |
|---|---|---|
| OSI Layer | Layer 4 (Transport) | Layer 7 (Application) |
| Traffic Type | TCP/UDP | HTTP/HTTPS |
| Health Probes | Port-based | URL/path-based |
| Routing | Basic round-robin | Intelligent routing (URL, header) |
| SSL Termination | ❌ Not supported | ✅ Supported |
| Web Application Firewall | ❌ Not available | ✅ Built-in |
| Use Case | VMs, RDP, custom protocols | Web apps, API gateways |
🔧 High-Level Setup Steps I Followed
For Azure Load Balancer:
- Created an Availability Set or VM Scale Set
- Created a Public Load Balancer
- Defined a Backend Pool (VMs)
- Added Health Probes
- Created Load Balancing Rules
For Application Gateway:
- Set up a Virtual Network with two subnets (one for App Gateway, one for backend)
- Created Application Gateway (WAF Tier)
- Configured Frontend IP, Listener, and Backend Pools
- Set up Routing Rules and HTTP settings
- Enabled SSL termination and custom domains
🧠 Tips from My Experience
- Always use Availability Sets or Zones with Load Balancer for fault tolerance
- Use Application Gateway + WAF to protect web apps from threats like SQL injection
- Enable custom health probes with specific paths like
/healthcheck - Combine App Gateway with Azure Front Door for global reach and CDN
- Monitor performance using Azure Monitor and Network Insights
🔚 Conclusion
Implementing Azure Load Balancer and Application Gateway gave me a powerful way to build highly available, secure, and scalable cloud architectures. Whether it’s distributing backend VM traffic or routing web requests intelligently, these tools are essential for any production-ready solution in Azure.
Start with Azure Load Balancer for basic scenarios, and upgrade to App Gateway when you need smarter web traffic handling and security.
