This method is used to achieve server affinity by binding a user to a particular backend, allowing work with a single application version. Herewith, on the first visit, the customer is routed based on the servers’ weights, while the assigned backend is remembered, ensuring that all subsequent requests from this user go to the same environment.
Commonly, this is implemented through remembering IP address, which is not optimal, as there could be a lot of customers behind a proxy, resulting in unfair balancing. Thus, the platform uses an advanced solution based on the session cookies to make a persistent routing, when each browser becomes an unique “user”, allowing to make balancing more even.
In such a way, Sticky Sessions distribution of a new user is similar to the round robin method and is performed according to the pre-set priority. For example, setting 50% to 50% will make both application versions be visited by an equal number of unique users, which is useful for performing A/B Testing. But, regardless of the server’s weights, the “old” user’s requests will always be redirected to the hosts they are assigned to, until their session expires or the cookie is removed.
