One of the fundamental features of Salt is remote execution. Salt has two basic "channels" for communicating with minions. Each channel requires a client (minion) and a server (master) implementation to work within Salt. These pairs of channels will work together to implement the specific message passing required by the channel interface. Channels use Transports for sending and receiving messages.
The pub (or pubish) channel is how a master sends a job (payload) to a minion. This is a basic pub/sub paradigm, which has specific targeting semantics. All data which goes across the publish system should be encrypted such that only members of the Salt cluster can decrypt the published payloads.
The req channel is how the minions send data to the master. This interface is
primarily used for fetching files and returning job returns. The req channels
have two basic interfaces when talking to the master.
send is the basic
method that guarantees the message is encrypted at least so that only minions
attached to the same master can read it-- but no guarantee of minion-master
confidentiality, whereas the
crypted_transfer_decode_dictentry method does
guarantee minion-master confidentiality. The req channel is also used by the
salt cli to publish jobs to the master.