Least Connections is a dynamic load balancing algorithm that directs incoming requests to the server with the fewest active connections at the time of assignment. Unlike Round Robin, which distributes requests evenly in a fixed sequence, Least Connections optimizes distribution based on real-time server load, making it particularly useful for applications with long-lived connections or varying request sizes.
When a request arrives, the load balancer:
Checks the number of active connections on each available server.
Assigns the request to the server with the fewest active connections, ensuring a more balanced workload.
Repeats the process dynamically, adjusting as connections open and close.
For example, if there are three servers handling traffic:
Server A: 10 active connections
Server B: 5 active connections
Server C: 3 active connections
A new request would be routed to Server C, as it currently has the lowest load.
Real-Time Load Awareness: Ensures traffic is balanced based on actual server utilization rather than a static rotation.
Optimized for Long-Lived Connections: Ideal for environments like databases, APIs, and streaming services, where some requests consume more resources than others.
Reduces Overloading Risks: Prevents one server from becoming overwhelmed while others remain underutilized.
Requires Continuous Monitoring: The load balancer must constantly track connection states, which may introduce slight overhead.
Not Always the Best for Short Requests: If traffic consists of many small, short-lived requests, the connection count may not accurately reflect server workload.
Does Not Account for Server Capacity Differences: A more powerful server might still get overloaded if all connections require high processing power. In such cases, Weighted Least Connections (assigning different weights to servers based on capacity) is often preferred.
API Gateways: Balancing traffic across backend microservices with varying processing times.
Database Load Balancing: Distributing queries across database replicas to prevent bottlenecks.
Reverse Proxy Servers: Ensuring web servers handling dynamic content don’t get overwhelmed.
Least Connections is an effective adaptive load balancing strategy, especially for applications where traffic patterns are unpredictable. By ensuring requests are sent to the least-burdened server, it helps maintain system stability and responsiveness in high-demand environments.