Last week, we described the concept behind sticky sessions: you forward a request to the same upstream because there’s context data associated with the session on that node. However, if necessary, you should replicate the data to other upstreams because this one might go down. In this post, we are going to illustrate it with a demo. The overall design Design options are limitless. I’ll keep myself to a familiar stack, the JVM.

Sticky sessions, also known as session affinity, is a mechanism by which a routing component that acts as a facade always routes a request to the same underlying upstream node. In this post, I’ll describe the reason behind sticky sessions, available alternatives, and how to implement them via Apache APISIX. Why sticky sessions? Sticky sessions became popular when we stored the state on the upstream node, not the database.