What is Load Balancing in Microservices?

Load balancing means distributing incoming requests across multiple instances of a service to:

• Improve performance

• Increase availability

• Avoid overloading a single instance

📌 Example:
Order Service has 3 instances → requests should be distributed among them.

🔹 Why Load Balancing is Needed?

Without load balancing:

• One instance gets overloaded

• Others remain idle

• High latency & failures

🔹 Types of Load Balancing

1️⃣ Server-side Load Balancing

• Load balancer sits before services

• Example: Nginx, AWS ELB

2️⃣ Client-side Load Balancing (Spring approach)

• Client decides which service instance to call

• Uses service discovery (Eureka/Consul)

👉 Spring Cloud LoadBalancer = Client-side

🔹 What is Spring Cloud LoadBalancer?

It is the replacement of Netflix Ribbon.

It:

• Works with service discovery

• Chooses a service instance

• Integrates with WebClient & Feign

🔹 How It Works (Flow)

1. Service registers with Eureka

2. Client asks Eureka for available instances

3. LoadBalancer selects one instance

4. Request is sent to that instance

🔹 Load Balancing Strategies

• Round Robin (default)

• Random

• Custom (based on metadata, zone, etc.)

🔹 Example Configuration

1️⃣ Dependency

2️⃣ Using WebClient

3️⃣ With Feign Client

🔹 Real-World Example

💳 Payment Service has 5 instances

• LoadBalancer distributes traffic

• If one instance goes down → others continue

🔹 Spring Cloud LoadBalancer vs Ribbon

🔥 Interview One-Liner

“Spring Cloud LoadBalancer provides client-side load balancing by selecting service instances dynamically using service discovery.”