Load Balancing

Load Balancer helps to spread the traffic across a cluster of servers to improve responsiveness and availability of applications, websites or databases. LB also keeps track of the status of all the resources while distributing requests. If a server is not available to take new requests or is not responding or has elevated error rate, LB will stop sending traffic to such a server.

Loading Balancing Algorithms

Health Checks

To monitor the health of a backend server, “health check” regularly attempts to connect to backend servers to ensure that servers are listening. If a server fails a health check, it is automatically removed from the pool, and traffic will not be forwarded to it until it responds to the health checks again.

• Least Connection Method
  • This method directs traffic to the server with the fewest active connections. This approach is quite useful when there are a large number of persistent client connections which are unevenly distributed between the servers.
• Least Response Time Method
  • This algorithm directs traffic to the server with the fewest active connections and the lowest average response time.
• Least Bandwidth method
  • This method selects the server that is currently serving the least amount of traffic measured in megabits per second (Mbps).
• Round Robin Method
  • This method cycles through a list of servers and sends each new request to the next server. It is most useful when the servers are of equal specification and there are not may persistent connections.
• Weighted Round Robin Method
  • The weighted round-robin scheduling is designed to better handle servers with different processing capacities. Each server is assigned a weight (an integer value that indicates the processing capacity). Servers with higher weights receive new connections before those with less weights and servers with higher weights get more connections than those with less weights.
• IP Hash
  • Under this method, a hash of the IP address of the client is calculated to redirect the request to a server.

Redundant Load Balancers

The load balancers can be a single point of failure; to overcome this, a second load balancer can be connected to the first to form a cluster. Each LB monitors the health of the other and, since both of them are equality capable of serving traffic and failure detection, in the event the main load balancer fails, the second load balancer takes over.