The diagram below shows 6 common algorithms.

Static Algorithms

1. Round robin
   The client requests are sent to different service instances in sequential order. The services are usually required to be stateless.

2. Sticky round-robin
   This is an improvement of the round-robin algorithm. If Alice’s first request goes to service A, the following requests go to service A as well.

3. Weighted round-robin
   The admin can specify the weight for each service. The ones with a higher weight handle more requests than others.

4. Hash
   This algorithm applies a hash function on the incoming requests’ IP or URL.

5. Least connections
   A new request is sent to the service instance with the least concurrent connections.

6. Least response time
   A new request is sent to the service instance with the fastest response time.

Over to you: We can use other attributes for hashing algorithms. For example, HTTP header, request type, client type, etc. What attributes have you used?