============= TCP Transport ============= The tcp transport is an implementation of Salt's channels using raw tcp sockets. Since this isn't using a pre-defined messaging library we will describe the wire protocol, message semantics, etc. in this document. The tcp transport is enabled by changing the :conf_minion:`transport` setting to ``tcp`` on each Salt minion and Salt master. .. code-block:: yaml transport: tcp .. warning:: We currently recommend that when using Syndics that all Masters and Minions use the same transport. We're investigating a report of an error when using mixed transport types at very heavy loads. Wire Protocol ============= This implementation over TCP focuses on flexibility over absolute efficiency. This means we are okay to spend a couple of bytes of wire space for flexibility in the future. That being said, the wire framing is quite efficient and looks like: .. code-block:: text msgpack({'head': SOMEHEADER, 'body': SOMEBODY}) Since msgpack is an iterably parsed serialization, we can simply write the serialized payload to the wire. Within that payload we have two items "head" and "body". Head contains header information (such as "message id"). The Body contains the actual message that we are sending. With this flexible wire protocol we can implement any message semantics that we'd like-- including multiplexed message passing on a single socket. TLS Support =========== .. versionadded:: 2016.11.1 The TCP transport allows for the master/minion communication to be optionally wrapped in a TLS connection. Enabling this is simple, the master and minion need to be using the tcp connection, then the `ssl` option is enabled. The `ssl` option is passed as a dict and corresponds to the options passed to the Python `ssl.wrap_socket ` function. A simple setup looks like this, on the Salt Master add the `ssl` option to the master configuration file: .. code-block:: yaml ssl: keyfile: certfile: ssl_version: PROTOCOL_TLSv1_2 The minimal `ssl` option in the minion configuration file looks like this: .. code-block:: yaml ssl: True # Versions below 2016.11.4: ssl: {} Specific options can be sent to the minion also, as defined in the Python `ssl.wrap_socket` function. .. note:: While setting the ssl_version is not required, we recommend it. Some older versions of python do not support the latest TLS protocol and if this is the case for your version of python we strongly recommend upgrading your version of Python. Crypto ====== The current implementation uses the same crypto as the ``zeromq`` transport. Pub Channel =========== For the pub channel we send messages without "message ids" which the remote end interprets as a one-way send. .. note:: As of today we send all publishes to all minions and rely on minion-side filtering. Req Channel =========== For the req channel we send messages with a "message id". This "message id" allows us to multiplex messages across the socket.