What is a Load Balancer?
A Load Balancer is a system (hardware or software) that distributes incoming network traffic across multiple servers (also called backend servers or nodes) to ensure:
- High availability
- Reliability
- Scalability
- Improved performance
It acts as a traffic manager, sitting between clients and servers to evenly distribute load and avoid server overload.
How Load Balancing Works
Here’s how the process works, step-by-step:
- Client Sends Request
A user (client) requests a web page, video, or API call. - Load Balancer Receives Request
Instead of going directly to a specific server, the request first hits the load balancer. - Request is Distributed Based on Algorithm
The load balancer uses a load balancing algorithm (explained below) to select one of the available backend servers. - Forward to Server
The request is forwarded to the selected server, which processes it and sends the response back—either directly to the client or via the load balancer. - Health Checks
Load balancers continuously monitor server health. If a server fails, it stops sending traffic to that server until it’s healthy again.
Common Load Balancing Algorithms
- Round Robin
Sends each request to the next server in a rotating order. - Least Connections
Sends requests to the server with the fewest active connections. - IP Hash
Uses the client’s IP address to determine which server handles the request. - Weighted Round Robin
Servers with higher capacity get more requests based on weight. - Random
Sends traffic to a random server (simple but sometimes inefficient).
Types of Load Balancers
| Type | Description |
|---|---|
| Hardware | Physical devices (e.g., F5, Cisco) used in enterprise settings |
| Software | Installed software like HAProxy, Nginx, or Apache |
| Cloud-based | Provided by cloud services like AWS ELB, Azure Load Balancer, etc. |
Real-World Example
Suppose you have an online store with 3 servers:
- If 1,000 users come at once,
- The load balancer might split them:
- 334 to Server A
- 333 to Server B
- 333 to Server C
If Server B crashes, the balancer routes all traffic to A and C only.
Benefits of Load Balancing
Security – Acts as a shield (in some setups).
Redundancy – Prevents downtime if one server fails.
Scalability – Easily add or remove servers.
Performance – Distributes workload efficiently.
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