In this video, you will learn about how do you set up the load balancing policy in an OCI Load Balancer. There are three possible load balancing policies you can use, which is weighted Round Robin, IP Hash, or least connection, which you choose when you provision the load balancer itself. You choose the type of load balancer shape, etc. You provision the load balancer in a particular subnet. If it is a public load balancer, of course, it is in a public subnet and you're choosing the second screen about the load balancing policy. How do these three load balancing policies help is to be understood. If I have three backend servers, for example, with the load balancer front ending it. A Round Robin typically means every client request that comes to the load balancer will get rounded to one of the backend servers in a Round Robin way. If you want, you can assign weights to the backend servers, which will be available for configuration after the load balancing is provisioned, wherein you can give for example, a two is to one is to one, wherein a typical reason why you would do that is depending on the shape of the compute instance that is running. Maybe specific compute instance you provisioned have more resources. Then for every two requests, one request will be forwarded to the other modes. That's about doing a Round Robin based load balancing. Whereas an IP Hash takes get off sending requests that are coming in from a particular source IP address to be always brought into a particular backend server. This can be used to identify all the requests coming in from a particular network to be routed to a particular backend server. But please keep in mind, this is not session stickiness or taking care of session persistence. We will come into that in a moment, hold on. Then you have the ability to use least connection based load balancing, wherein if various requests have come in and the client requests are forwarded to particular nodes, but over a period of time, specific sessions on a particular node are completed with respect to the work that they have done, then it is quite possible you have nodes which are having lesser work, then least connection based routing can also happen. The load balancing policy decisions apply differently for standard TCP load balancers where no session stickiness is implemented, or if you implement session persistence with cookie-based sessions, you have the ability to enable cookie-based session persistence such that whenever a client has initiated a connection, every request has to go to the same server that will depend on how you configure your application, certain applications with some session specific data into that backend server, in which case, all requests thereafter would have to come to that particular node only for that particular client. To implement that, you use cookies. Cookies are chosen in either one of the following two ways. If you go to "Advanced Options" and choose "Session persistence", without this session persistence, then the normal load balancing policy you specify works, but you can ask the load balancer to use a cookie that is generated by the application nodes and use that to route the traffic to the same node again and again based on where the session was established, or you can ask the load balancer to generate a cookie and identify the session and distribute the load. The moment you have session persistence enabled, then obviously, the load balancing policy is not going to be used. Whereas if you don't have session persistence implemented, then the load balancing policy that you specify will be used, and the load balancing policy that you specify will come into work as to how the backend servers are loaded. With that, we come to understand about how do you choose the load balancing policy fundamentally based on the application architecture, whether session stickiness is required or not is the first thing you need to consider. Then if session stickiness is required, you choose the cookie-based session stickiness to be implemented. If not, you use one of the load balancing policies that OCI offers.
