mirror of
https://github.com/valitydev/salt.git
synced 2024-11-07 17:09:03 +00:00
247 lines
8.4 KiB
ReStructuredText
247 lines
8.4 KiB
ReStructuredText
.. _salt_architecture:
|
|
|
|
Overview
|
|
========
|
|
|
|
In its most typical use, Salt is a software application in which clients,
|
|
called "minions" can be commanded and controlled from a central command server
|
|
called a "master".
|
|
|
|
Commands are normally issued to the minions (via the master) by calling a
|
|
client script simply called, 'salt'.
|
|
|
|
Salt features a pluggable transport system to issue commands from a master to
|
|
minions. The default transport is ZeroMQ.
|
|
|
|
Salt Client
|
|
===========
|
|
|
|
Overview
|
|
--------
|
|
|
|
The salt client is run on the same machine as the Salt Master and communicates
|
|
with the salt-master to issue commands and to receive the results and display
|
|
them to the user.
|
|
|
|
The primary abstraction for the salt client is called 'LocalClient'.
|
|
|
|
When LocalClient wants to publish a command to minions, it connects to the
|
|
master by issuing a request to the master's ReqServer (TCP: 4506)
|
|
|
|
The LocalClient system listens to responses for its requests by listening to
|
|
the master event bus publisher (master_event_pub.ipc).
|
|
|
|
Salt Master
|
|
===========
|
|
|
|
Overview
|
|
--------
|
|
|
|
The salt-master daemon runs on the designated Salt master and performs
|
|
functions such as authenticating minions, sending, and receiving requests
|
|
from connected minions and sending and receiving requests and replies to the
|
|
'salt' CLI.
|
|
|
|
Moving Pieces
|
|
-------------
|
|
|
|
When a Salt master starts up, a number of processes are started, all of which
|
|
are called 'salt-master' in a process-list but have various role categories.
|
|
|
|
Among those categories are:
|
|
|
|
* Publisher
|
|
* EventPublisher
|
|
* MWorker
|
|
|
|
Publisher
|
|
---------
|
|
|
|
The Publisher process is responsible for sending commands over the designated
|
|
transport to connected minions. The Publisher is bound to the following:
|
|
|
|
* TCP: port 4505
|
|
* IPC: publish_pull.ipc
|
|
|
|
Each salt minion establishes a connection to the master Publisher.
|
|
|
|
EventPublisher
|
|
--------------
|
|
|
|
The EventPublisher publishes events onto the event bus. It is bound to the
|
|
following:
|
|
|
|
* IPC: master_event_pull.ipc
|
|
* IPC: master_event_pub.ipc
|
|
|
|
MWorker
|
|
-------
|
|
|
|
Worker processes manage the back-end operations for the Salt Master.
|
|
|
|
The number of workers is equivalent to the number of 'worker_threads'
|
|
specified in the master configuration and is always at least one.
|
|
|
|
Workers are bound to the following:
|
|
|
|
* IPC: workers.ipc
|
|
|
|
ReqServer
|
|
---------
|
|
|
|
The Salt request server takes requests and distributes them to available MWorker
|
|
processes for processing. It also receives replies back from minions.
|
|
|
|
The ReqServer is bound to the following:
|
|
* TCP: 4506
|
|
* IPC: workers.ipc
|
|
|
|
Each salt minion establishes a connection to the master ReqServer.
|
|
|
|
|
|
Job Flow
|
|
--------
|
|
|
|
The Salt master works by always publishing commands to all connected minions
|
|
and the minions decide if the command is meant for them by checking themselves
|
|
against the command target.
|
|
|
|
The typical lifecycle of a salt job from the perspective of the master
|
|
might be as follows:
|
|
|
|
1) A command is issued on the CLI. For example, 'salt my_minion test.ping'.
|
|
|
|
2) The 'salt' command uses LocalClient to generate a request to the salt master
|
|
by connecting to the ReqServer on TCP:4506 and issuing the job.
|
|
|
|
3) The salt-master ReqServer sees the request and passes it to an available
|
|
MWorker over workers.ipc.
|
|
|
|
4) A worker picks up the request and handles it. First, it checks to ensure
|
|
that the requested user has permissions to issue the command. Then, it sends
|
|
the publish command to all connected minions. For the curious, this happens
|
|
in ClearFuncs.publish().
|
|
|
|
5) The worker announces on the master event bus that it is about to publish
|
|
a job to connected minions. This happens by placing the event on the master
|
|
event bus (master_event_pull.ipc) where the EventPublisher picks it up and
|
|
distributes it to all connected event listeners on master_event_pub.ipc.
|
|
|
|
6) The message to the minions is encrypted and sent to the Publisher via IPC
|
|
on publish_pull.ipc.
|
|
|
|
7) Connected minions have a TCP session established with the Publisher on TCP
|
|
port 4505 where they await commands. When the Publisher receives the job over
|
|
publish_pull, it sends the jobs across the wire to the minions for processing.
|
|
|
|
8) After the minions receive the request, they decrypt it and perform any
|
|
requested work, if they determine that they are targeted to do so.
|
|
|
|
9) When the minion is ready to respond, it publishes the result of its job back
|
|
to the master by sending the encrypted result back to the master on TCP 4506
|
|
where it is again picked up by the ReqServer and forwarded to an available
|
|
MWorker for processing. (Again, this happens by passing this message across
|
|
workers.ipc to an available worker.)
|
|
|
|
10) When the MWorker receives the job it decrypts it and fires an event onto
|
|
the master event bus (master_event_pull.ipc). (Again for the curious, this
|
|
happens in AESFuncs._return().
|
|
|
|
11) The EventPublisher sees this event and re-publishes it on the bus to all
|
|
connected listeners of the master event bus (on master_event_pub.ipc). This
|
|
is where the LocalClient has been waiting, listening to the event bus for
|
|
minion replies. It gathers the job and stores the result.
|
|
|
|
12) When all targeted minions have replied or the timeout has been exceeded,
|
|
the salt client displays the results of the job to the user on the CLI.
|
|
|
|
|
|
Salt Minion
|
|
===========
|
|
|
|
Overview
|
|
--------
|
|
|
|
The salt-minion is a single process that sits on machines to be managed by
|
|
Salt. It can either operate as a stand-alone daemon which accepts commands
|
|
locally via 'salt-call' or it can connect back to a master and receive commands
|
|
remotely.
|
|
|
|
When starting up, salt minions connect _back_ to a master defined in the minion
|
|
config file. The connect to two ports on the master:
|
|
|
|
* TCP: 4505
|
|
This is the connection to the master Publisher. It is on this port that
|
|
the minion receives jobs from the master.
|
|
|
|
* TCP: 4506
|
|
This is the connection to the master ReqServer. It is on this port that
|
|
the minion sends job results back to the master.
|
|
|
|
|
|
Event System
|
|
------------
|
|
|
|
Similar to the master, a salt-minion has its own event system that operates
|
|
over IPC by default. The minion event system operates on a push/pull system
|
|
with IPC files at minion_event_<unique_id>_pub.ipc and
|
|
minion_event_<unique_id>_pull.ipc.
|
|
|
|
The astute reader might ask why have an event bus at all with a single-process
|
|
daemon. The answer is that the salt-minion may fork other processes as required
|
|
to do the work without blocking the main salt-minion process and this
|
|
necessitates a mechanism by which those processes can communicate with each
|
|
other. Secondarily, this provides a bus by which any user with sufficient
|
|
permissions can read or write to the bus as a common interface with the salt
|
|
minion.
|
|
|
|
|
|
Job Flow
|
|
--------
|
|
|
|
When a salt minion starts up, it attempts to connect to the Publisher and the
|
|
ReqServer on the salt master. It then attempts to authenticate and once the
|
|
minion has successfully authenticated, it simply listens for jobs.
|
|
|
|
Jobs normally come either come from the 'salt-call' script run by a local user
|
|
on the salt minion or they can come directly from a master.
|
|
|
|
Master Job Flow
|
|
---------------
|
|
|
|
1) A master publishes a job that is received by a minion as outlined by the
|
|
master's job flow above.
|
|
|
|
2) The minion is polling its receive socket that's connected to the master
|
|
Publisher (TCP 4505 on master). When it detects an incoming message, it picks it
|
|
up from the socket and decrypts it.
|
|
|
|
3) A new minion process or thread is created and provided with the contents of the
|
|
decrypted message. The _thread_return() method is provided with the contents of
|
|
the received message.
|
|
|
|
4) The new minion thread is created. The _thread_return() function starts up
|
|
and actually calls out to the requested function contained in the job.
|
|
|
|
5) The requested function runs and returns a result. [Still in thread.]
|
|
|
|
6) The result of the function that's run is encrypted and returned to the
|
|
master's ReqServer (TCP 4506 on master). [Still in thread.]
|
|
|
|
7) Thread exits. Because the main thread was only blocked for the time that it
|
|
took to initialize the worker thread, many other requests could have been
|
|
received and processed during this time.
|
|
|
|
|
|
A Note on ClearFuncs vs. AESFuncs
|
|
=================================
|
|
|
|
A common source of confusion is determining when messages are passed in the
|
|
clear and when they are passed using encryption. There are two rules governing
|
|
this behaviour:
|
|
|
|
1) ClearFuncs is used for intra-master communication and during the initial
|
|
authentication handshake between a minion and master during the key exhange.
|
|
|
|
2) AESFuncs is used everywhere else.
|