Azure Load Balancer vs Application Gateway: Key Differences and Use Cases

In Azure, a Load Balancer distributes incoming network traffic at the transport layer (TCP/UDP) for high availability, while an Application Gateway works at the application layer (HTTP/HTTPS) and offers advanced routing and security features. Use Load Balancer for simple, fast traffic distribution and Application Gateway for web traffic management with SSL termination and web application firewall.

Quick Comparison

This table summarizes the main differences between Azure Load Balancer and Application Gateway.

Feature	Azure Load Balancer	Azure Application Gateway
OSI Layer	Transport Layer (Layer 4)	Application Layer (Layer 7)
Protocol Support	TCP, UDP	HTTP, HTTPS
Routing Type	Basic traffic distribution	URL-based routing, path-based routing
SSL Termination	No	Yes
Web Application Firewall (WAF)	No	Yes
Use Case	Load balancing VMs or services with TCP/UDP traffic	Managing web traffic with advanced routing and security

Key Differences

Azure Load Balancer works at the transport layer, meaning it routes traffic based on IP address and port without inspecting the content. It supports TCP and UDP protocols and is ideal for distributing traffic to virtual machines or services that require fast, simple load balancing.

In contrast, Azure Application Gateway operates at the application layer. It understands HTTP and HTTPS traffic, allowing it to make routing decisions based on URL paths or host headers. This enables features like SSL termination, where encrypted traffic is decrypted at the gateway, and integration with a Web Application Firewall (WAF) to protect against common web attacks.

Because of these differences, Load Balancer is best for non-HTTP workloads or when you need ultra-low latency, while Application Gateway is suited for web applications needing advanced routing, security, and session affinity.

Code Comparison

Here is an example of creating an Azure Load Balancer with a backend pool and health probe using Azure CLI.

bash

az network lb create --resource-group MyResourceGroup --name MyLoadBalancer --sku Standard --frontend-ip-name MyFrontEnd --backend-pool-name MyBackEndPool

az network lb probe create --resource-group MyResourceGroup --lb-name MyLoadBalancer --name MyHealthProbe --protocol tcp --port 80

az network lb rule create --resource-group MyResourceGroup --lb-name MyLoadBalancer --name MyLoadBalancerRule --protocol tcp --frontend-port 80 --backend-port 80 --frontend-ip-name MyFrontEnd --backend-pool-name MyBackEndPool --probe-name MyHealthProbe

Output

Creates a standard Load Balancer with a TCP health probe on port 80 and a load balancing rule forwarding traffic from frontend port 80 to backend pool.

Application Gateway Equivalent

Here is an example of creating an Azure Application Gateway with a frontend IP, backend pool, HTTP settings, and a basic routing rule using Azure CLI.

bash

az network application-gateway create --name MyAppGateway --location eastus --resource-group MyResourceGroup --capacity 2 --sku Standard_v2 --frontend-port 80 --http-settings-cookie-based-affinity Enabled --http-settings-port 80 --http-settings-protocol Http --routing-rule-type Basic --backend-pool-name MyBackendPool --frontend-ip-name MyFrontEndIP

Output

Creates an Application Gateway with HTTP frontend on port 80, backend pool, and routing rule with cookie-based affinity enabled.

When to Use Which

Choose Azure Load Balancer when you need fast, simple load distribution for TCP or UDP traffic without inspecting the content, such as for databases, gaming servers, or non-HTTP services.

Choose Azure Application Gateway when managing web traffic that requires advanced routing, SSL termination, or protection with a Web Application Firewall, such as for websites, APIs, or microservices.

In summary, use Load Balancer for network-level traffic and Application Gateway for web application-level traffic.

Key Takeaways

Azure Load Balancer works at Layer 4 for TCP/UDP traffic, offering simple, fast load distribution.

Azure Application Gateway works at Layer 7 for HTTP/HTTPS with advanced routing and security features.

Use Load Balancer for non-web workloads needing high performance and low latency.

Use Application Gateway for web apps needing SSL termination, URL-based routing, and WAF protection.

Choosing the right service depends on your traffic type and security needs.