Is Consistent Hashing used in Load Balancer?

Yes, Consistent Hashing is commonly used in load balancers to distribute traffic across a set of backend servers or nodes.

Below is an explanation of how it works:

1. Hashing Requests

When a client sends a request to a load balancer, the load balancer calculates a hash of the request’s attributes (such as source IP address, destination IP address, source port, destination port, protocol, etc.).

2. Mapping to Backend Servers

The hash value is then used to map the request to one of the available backend servers. Each server is represented by a point on a hash ring (a virtual ring), and the hash value determines which point (and thus, which server) the request is routed to.

3. Consistency

The “consistent” part of consistent hashing comes from the fact that, unlike traditional hashing methods, adding or removing a server from the pool does not significantly change the mapping of requests to servers. Only a portion of the requests are remapped to different servers, minimizing disruptions.

4. Load Balancing

Consistent hashing helps in distributing the load evenly across servers, as requests are mapped to servers based on their hash values. This ensures that servers are not overloaded while others remain underutilized.

5. Session Persistence

Consistent hashing also allows for session persistence (or “sticky sessions”), where requests from the same client are consistently routed to the same backend server. This is useful for maintaining stateful connections, such as in web applications that require users to stay connected to the same server for the duration of their session.

Overall, consistent hashing in load balancers provides a scalable and efficient way to distribute traffic across backend servers while maintaining a degree of consistency and minimizing disruptions during server additions or removals.