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When a single WSO2 product is providing a service, a session object is created and remains in the memory of the WSO2 product. However, in a clustered environment, where you could have multiple WSO2 product servers fronted by a load balancer to balance the load among these products, the situation is a little different.
If WSO2 server A does task X, WSO2 server B does task Y and WSO2 server C does task Z, and each one has a session object, there is no way for one WSO2 server to know what the other is doing. So, in order to synchronize between these servers, sticky sessions are used.
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