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AWS Load Balancer: Overview, Types, and Components
In cloud architectures, handling high traffic efficiently is crucial. A load balancer distributes incoming traffic across multiple resources (like EC2 instances) to ensure high availability, fault tolerance, and scalability.
AWS offers Elastic Load Balancing (ELB) — a fully managed service that automatically distributes incoming application or network traffic.
🌟 1. What is a Load Balancer?
A Load Balancer (LB) acts as a traffic manager for your application:
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Distributes requests across multiple targets (EC2, containers, IP addresses).
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Ensures no single instance is overloaded.
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Increases fault tolerance — if one target fails, traffic is redirected to healthy targets.
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Supports secure connections using SSL/TLS.
Real-world analogy: Think of a cashier line in a supermarket. The load balancer is like the manager directing customers to the shortest or fastest line, so everyone is served efficiently.
⚙️ 2. Types of AWS Load Balancers
AWS offers 3 main types of load balancers under Elastic Load Balancing:
| Load Balancer | Protocol / Layer | Use Case |
|---|---|---|
| Application Load Balancer (ALB) | HTTP / HTTPS (Layer 7) | Web applications, advanced routing, microservices, container-based apps |
| Network Load Balancer (NLB) | TCP / UDP / TLS (Layer 4) | Ultra-low latency, high-performance apps, millions of requests per second, static IP requirements |
| Gateway Load Balancer (GLB) | IP traffic (Layer 3) | Third-party virtual appliances, security appliances, firewalls, monitoring appliances |
🔹 Application Load Balancer (ALB)
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Operates at Layer 7 (Application Layer)
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Supports path-based and host-based routing
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Ideal for microservices and containerized apps
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Supports HTTP/HTTPS and WebSocket protocols
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Can integrate with AWS WAF (Web Application Firewall) for security
Example:
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Route
/images/*traffic to an EC2 group for image servers -
Route
/api/*traffic to another EC2 group running your APIs
🔹 Network Load Balancer (NLB)
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Operates at Layer 4 (Transport Layer)
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Extremely fast and can handle millions of requests per second
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Ideal for TCP/UDP applications
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Supports static IP addresses and Elastic IPs
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Best for low latency applications, such as gaming servers, IoT, or financial apps
🔹 Gateway Load Balancer (GLB)
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Operates at Layer 3 (Network Layer)
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Distributes traffic to third-party virtual appliances like firewalls or intrusion detection systems
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Used in advanced security, monitoring, and network inspection setups
🔄 3. Key Differences Between Load Balancers
| Feature | ALB | NLB | GLB |
|---|---|---|---|
| Layer | 7 | 4 | 3 |
| Protocols | HTTP/HTTPS/WebSocket | TCP/UDP/TLS | IP |
| Use Case | Web apps, microservices | High-performance apps, low latency | Security appliances, virtual appliances |
| Routing | Host/path-based | Flow hash (IP/port) | Forward traffic to appliances |
| Static IP | ❌ | ✅ | ✅ |
| TLS Termination | ✅ | ✅ | ❌ |
| Health Checks | Application-based | TCP/HTTP | IP-based |
🧩 4. Components of AWS Load Balancers
AWS Load Balancers are made up of several key components:
| Component | Description |
|---|---|
| Listeners | Define protocol and port (e.g., HTTP:80, HTTPS:443) that the LB listens on. |
| Target Groups | Logical grouping of EC2 instances, IP addresses, or Lambda functions that receive traffic. |
| Rules | Define how the LB routes requests to target groups (ALB only). Supports host/path-based routing. |
| Health Checks | Periodically check if targets are healthy; unhealthy targets don’t receive traffic. |
| Security Groups / Network ACLs | Control inbound/outbound traffic to the LB (ALB/NLB). |
| Cross-Zone Load Balancing | Distributes traffic evenly across multiple AZs for fault tolerance. |
🧠 5. Choosing the Right Load Balancer
| Scenario | Recommended LB |
|---|---|
| Web application with HTTP/HTTPS | ALB |
| API Gateway or microservices with path/host routing | ALB |
| Ultra-low latency TCP app | NLB |
| Security appliances or firewall deployment | GLB |
| Mixed web + TCP traffic | Use ALB + NLB combo |
6. Best Practices
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Use ALB for web apps and NLB for low-latency apps.
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Enable cross-zone load balancing for HA.
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Use AWS WAF with ALB for added security.
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Regularly monitor CloudWatch metrics: RequestCount, HealthyHostCount, Latency, etc.
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Configure sticky sessions only when needed.