Failover Capability

  • If one server goes offline, all the traffic will be routed to other servers by Load Balancer. This prevents the website from going offline or the downtime incurred by spinning up a new server
  • We will also add a new healthy web server to the server pool to balance the load
  • Thus making the system Fault Tolerance (容错性)


  • If the traffic grows rapidly, and current set of servers are not enough to handle the traffic
  • We only need to add more servers to the server pool, and the Load Balancer automatically starts to send requests to them

Load-balancing Strategies

Round-Robin Load-balancing

  • Load Balancer distributes incoming requests equally among the available Server in a circular order. Simple and straightforward
  • Usually the default load-balancing strategy, for example in AWS ALB

Weighted Round Robin Load-balancing


Sticky Session

  • Also known as session affinity or session persistence
  • Refers to the practice of directing a Client’s requests to the same Server consistently for the duration of a session or user’s interaction