Application Load Balancer Overview
An Application Load Balancer (ALB) is a Layer 7 load balancer that distributes HTTP/HTTPS traffic across multiple backend targets. It improves availability, scalability, and security by intelligently routing requests based on content such as URL paths, host headers, or query strings.
Core Concepts
- Layer 7 routing: Operates at the application layer, enabling content-based routing.
- Traffic distribution: Balances requests across servers, containers, or services.
- Health checks: Ensures only healthy targets receive traffic.
- SSL/TLS termination: Offloads encryption/decryption from backend servers.
- Scalability: Handles millions of requests per second with auto-scaling.
AWS Application Load Balancer (ALB)
AWS offers Elastic Load Balancing (ELB), with ALB as its Layer 7 option.
Key Features
- Targets: EC2 instances, ECS/EKS containers, IP addresses, AWS Lambda.
- Listener rules: Route requests based on path (
/api/*), host (example.com), or headers. - Security: Integrates with AWS WAF, IAM, and VPC security groups.
- Scaling: Auto-scales across multiple Availability Zones.
- Algorithms: Round-robin or least outstanding requests.
Use Cases
- Microservices architectures
- Containerized workloads (ECS/EKS)
- Serverless applications with Lambda
Azure Application Gateway
Azure’s Application Gateway is its Layer 7 load balancer, optimized for enterprise workloads.
Key Features
- Targets: VMs, VM scale sets, App Services, AKS workloads.
- Security: Built-in WAF, DDoS protection, bot manager, Sentinel integration.
- SSL/TLS: SSL offload, end-to-end SSL, Key Vault integration for certificates.
- Advanced routing: URL rewrite, header modification, path-based routing.
- Scaling: Autoscaling with zone redundancy.
Use Cases
- Enterprise web applications
- Secure multi-region deployments
- Compliance-heavy workloads
AWS ALB vs Azure Application Gateway
| Feature | AWS ALB | Azure Application Gateway |
|---|---|---|
| Routing | Path, host, header, query string | Path, host, header, URL rewrite |
| Targets | EC2, ECS/EKS, IP, Lambda | VMs, VMSS, App Service, AKS |
| Security | AWS WAF, IAM, SGs | WAF, DDoS, Bot Manager, Sentinel |
| SSL/TLS | Termination, mutual TLS | SSL offload, end-to-end SSL, Key Vault |
| Scaling | Auto across AZs | Auto + zone redundancy |
| Specialties | Serverless + containers | Enterprise security + compliance |
