Add Message Routing section to docs

7 years ago · 9ca39dcf72
parent 65d5844d1a
commit 9ca39dcf72
5 changed files with 1186 additions and 0 deletions
--- a/docs/howitworks.rst
+++ b/docs/howitworks.rst
@ -395,6 +395,58 @@ presence of many machines, and would require manually splitting up the parts of
 Twisted that we would like to use.
 Message Routing
 ---------------
 At present routing is very simple, and assumes that it is impossible for a tree
 of contexts to be constructed such that at least one of a context's indirect
 parents will not know the ID of a target the context is attempting to
 communicate with.
 When :py:class:`econtext.core.Router` receives a message, it first checks the
 IDs associated with its directly connected streams for a potential route for
 the message. If one of the streams matches, either because the stream directly
 connects to the target ID, or the master has sent an ``ADD_ROUTE`` message
 associating that stream with the target ID, then the message will be forwarded
 down the tree using that stream.
 If the message does not match any ``ADD_ROUTE`` message or directly connected
 stream, instead it is forwarded upstream, first to the context's parent, and
 recursively by the each parent context in turn, until some tree node is reached
 that knows how to forward the message back down the tree.
 When the master establishes a new context via an existing child context, it
 takes care to send corresponding ``ADD_ROUTE`` messages to each indirect parent
 up the tree.
 Example
 #######
 .. image:: images/context-tree.png
 In the diagram, when ``master`` is establishing a connection to
 ``sudo:node12b:webapp``, it must send ``ADD_ROUTE`` messages to ``rack12``,
 ``dc1``, and ``bastion``; `node12b` does not require an ``ADD_ROUTE`` message
 since it has a stream directly connected to the new context.
 When ``sudo:node22a:webapp`` wants to send a message to
 ``sudo:node12b:webapp``, the message will be routed as follows:
 ``sudo:node22a:webapp -> node22a -> rack22 -> dc2 -> bastion -> dc1 -> rack12 -> node12b -> sudo:node12b:webapp``
 .. image:: images/route.png
 Future
 ######
 The current routing approach is incomplete, since routes to downstream contexts
 are not propagated upwards when a descendant of the master context establishes
 a new child context, but that is okay for now, since child contexts cannot
 currently allocate new context IDs anyway.
 Differences Between Master And Slave Brokers
 ############################################
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