Salt's architecture is based on the publish-subscribe pattern, known colloquially as pub/sub. In this design, one or more clients subscribe to a message queue. When a message is published to the queue, any current subscribers receive a copy, which they usually process in some way.
Salt in fact makes use of two message queues, both of which are managed by the Master. The first is used by the Master to publish commands to its Minions. Each Minion can see the messages published to this queue, but they will only react to them if the Minions are included in the target. A message targeted to '*'
will be processed by all Minions that are connected, whereas one targeted to 192.168.0.0/16
using the -s
command-line option will only be processed by Minions whose IP address starts with 192.168
.
The second message queue is also hosted by the Master, but messages are published to it from Minions, and the Master itself is the subscriber. These messages are normally stored in...