Workers, the Scheduler, and Clients communicate by sending each other Python objects (such as :ref:`protocol` messages or user data). The communication layer handles appropriate encoding and shipping of those Python objects between the distributed endpoints. The communication layer is able to select between different transport implementations, depending on user choice or (possibly) internal optimizations.
The communication layer lives in the :mod:`distributed.comm` package.
Communication addresses are canonically represented as URIs, such as
tcp://127.0.0.1:1234. For compatibility with existing code, if the
URI scheme is omitted, a default scheme of
tcp is assumed (so
127.0.0.1:456 is really the same as
The default scheme may change in the future.
The following schemes are currently implemented in the
tcpis the main transport; it uses TCP sockets and allows for IPv4 and IPv6 addresses.
tlsis a secure transport using the well-known TLS protocol over TCP sockets. Using it requires specifying keys and certificates as outlined in :ref:`tls`.
inprocis an in-process transport using simple object queues; it eliminates serialization and I/O overhead, providing almost zero-cost communication between endpoints as long as they are situated in the same process.
Some URIs may be valid for listening but not for connecting.
For example, the URI
tcp:// will listen on all IPv4 and IPv6 addresses
and on an arbitrary port, but you cannot connect to that address.
Higher-level APIs in
distributed may accept other address formats for
convenience or compatibility, for example a
(host, port) pair. However,
the abstract communications layer always deals with URIs.
There are a number of top-level functions in :mod:`distributed.comm` to help deal with addresses:
.. autofunction:: distributed.comm.parse_address
.. autofunction:: distributed.comm.unparse_address
.. autofunction:: distributed.comm.normalize_address
.. autofunction:: distributed.comm.resolve_address
.. autofunction:: distributed.comm.get_address_host
The basic unit for dealing with established communications is the
.. autoclass:: distributed.comm.Comm :members:
You don't create
Comm objects directly: you either
incoming communications, or
connect to a peer listening for connections:
.. autofunction:: distributed.comm.connect
.. autofunction:: distributed.comm.listen
Listener objects expose the following interface:
.. autoclass:: distributed.comm.core.Listener :members:
Extending the Communication Layer
Each transport is represented by a URI scheme (such as
backed by a dedicated :class:`Backend` implementation, which provides
entry points into all transport-specific routines.
.. autoclass:: distributed.comm.registry.Backend :members: