What is the "Ring Hash" Load-Balancing Algorithm?

What is the "Ring Hash" load-balancing algorithm... and how does Distributed Cloud HTTP Load-Balancing use it?

F5 Distributed Cloud (XC) condenses some features that are managed in different places in the more familiar world of BIG-IP, and a question that comes up is what are the XC LB algorithms and how is persistence configured?

If you look at the algorithms in the Console or API, you'll see a readout like this:

Several times "Consistent Hashing Algorithm" is referenced. Like "Least Sessions" or "Round Robin," Consistent Hashing Algorithm is its own algorithm. Imagine clients and servers on a ring, with server (origin) nodes evenly distributed between clients in the hash table. The purpose of this kind of algorithm is to tolerate dynamic addition or subtraction of nodes with the minimum amount of remapping between clients and nodes. See this article for more information about the algorithm.

For the "Cookie Based Stickiness" algorithm, F5 Distributed Cloud will create hash values in this ring that control persistence of requests between clients and origins based on Cookie value. You can specify other values in the protocol to base the hash on in the Ring Hash Policy option.

In summary, Consistent Hashing Algorithm tolerates dynamic changes in pool membership with the least amount of connection re-mapping for a more consistent session map. Persistence on top of this algorithm can be mapped to a protocol value such as a cookie.

See https://docs.cloud.f5.com/docs/how-to/app-networking/http-load-balancer for configuration guidance.