Describe the Router.

draft/high-level-architecture.rst

@@ -273,6 +273,26 @@ The Publisher will later retry publishing the message.
 Router
 ------
 
+In Celery 4.x there was a master process which consumes :term:`Messages <Message>`
+and workers which process them.
+
+In Celery we now decouple the execution of the tasks completely from the routing of :term:`Messages <Message>`
+to the `Execution Platform`_.
+
+The Router is a combination of the following architectural patterns:
+- :term:`Event Driven Consumer`
+- :term:`Message Dispatcher`
+- :term:`Service Activator`
+- :term:`Process Manager`.
+
+The Router consumes :term:`Messages <Message>` from a :term:`Message Broker` cluster or multiple clusters,
+dispatches the consumed :term:`Messages <Message>` to the `Execution Platform`_ for processing and awaits
+for the results of the task and stores them in the appropriate `Data Sink(s) <Data Sinks>`_.
+
+When the execution of a task requires coordination in case of a workflow, an :term:`Event Message` or an incoming
+:term:`Document Message` from a `Data Source <Data Sources>`_ the Router is responsible for the order of the execution
+of the task(s).
+
 Execution Platform
 ------------------
 

glossary.rst

@@ -41,11 +41,19 @@ Glossary
     but will produce the same side effects when facing duplicated messages.
 
   Message Dispatcher
-
     `Enterprise Integration Patterns`_ defines a `Message Dispatcher`_ as a
     component that will consume messages from a channel and distribute them to
     performers.
 
+  Process Manager
+    `Enterprise Integration Patterns`_ defines a `Process Manager`_ as a component
+    that maintains the state of the sequence and determines the next processing step
+    based on intermediate results.
+
+  Event Driven Consumer
+    `Enterprise Integration Patterns`_ defines an `Event Driven Consumer`_ as a component
+    that consumes a message as soon as it is delivered.
+
   Circuit Breaker
     Martin Fowler defines a `Circuit Breaker`_ in the following fashion:
 
@@ -297,4 +305,6 @@ CC0 1.0 Universal license (https://creativecommons.org/publicdomain/zero/1.0/dee
 .. _Inter-process Communication: https://en.wikipedia.org/wiki/Inter-process_communication
 .. _Domain Event: https://martinfowler.com/eaaDev/DomainEvent.html
 .. _Domain Model: https://martinfowler.com/eaaCatalog/domainModel.html
-.. _GIL: https://realpython.com/python-gil/
+.. _GIL: https://realpython.com/python-gil/
+.. _Process Manager: https://www.enterpriseintegrationpatterns.com/patterns/messaging/ProcessManager.html
+.. _Event Driven Consumer: https://www.enterpriseintegrationpatterns.com/patterns/messaging/EventDrivenConsumer.html