guides/user/Distributed-components.md

+# Distributed components (Dispatchers and Instances)
+
+Let's start with the definitions:
+
+An **_Instance_** is a scanner server which can be operated via a remote procedure call protocol -- simple enough.
+
+A **_Dispatcher_** is a server which provides clients with _Instances_.
+Its main job is to maintain a pool of _Instances_ and whenever a clients issues
+a _dispatch_ call to pop one from the pool and give its connection details to the client.
+
+Just as importantly, it's responsible for never letting the pool deplete by replenishing it after every _dispatch_ call.
+
+The aforementioned connection details include the URL of the Instance (_host:port_) and its authentication token,
+you can imagine what happens after that.
+
+Both servers use the same RPC protocol, [Arachni-RPC](https://github.com/Arachni/arachni-rpc),
+but they, of course, have different [APIs](https://github.com/Arachni/arachni/wiki/RPC-API).
+
+**Notice**
+
+The above is the simple version, in reality both the Instance and Dispatcher servers
+are much more elaborate systems; more about that in the [[High Performance Grid | HPG]] section.