The RAET Transport

注解

The RAET transport is in very early development, it is functional but no promises are yet made as to its reliability or security. As for reliability and security, the encryption used has been audited and our tests show that raet is reliable. With this said we are still conducting more security audits and pushing the reliability. This document outlines the encryption used in RAET

2014.7.0 新版功能.

The Reliable Asynchronous Event Transport, or RAET, is an alternative transport medium developed specifically with Salt in mind. It has been developed to allow queuing to happen up on the application layer and comes with socket layer encryption. It also abstracts a great deal of control over the socket layer and makes it easy to bubble up errors and exceptions.

RAET also offers very powerful message routing capabilities, allowing for messages to be routed between processes on a single machine all the way up to processes on multiple machines. Messages can also be restricted, allowing processes to be sent messages of specific types from specific sources allowing for trust to be established.

Using RAET in Salt

Using RAET in Salt is easy, the main difference is that the core dependencies change, instead of needing pycrypto, M2Crypto, ZeroMQ, and PYZMQ, the packages libsodium, libnacl, ioflo, and raet are required. Encryption is handled very cleanly by libnacl, while the queueing and flow control is handled by ioflo. Distribution packages are forthcoming, but libsodium can be easily installed from source, or many distributions do ship packages for it. The libnacl and ioflo packages can be easily installed from pypi, distribution packages are in the works.

Once the new deps are installed the 2014.7 release or higher of Salt needs to be installed.

Once installed, modify the configuration files for the minion and master to set the transport to raet:

/etc/salt/master:

transport: raet

/etc/salt/minion:

transport: raet

Now start salt as it would normally be started, the minion will connect to the master and share long term keys, which can then in turn be managed via salt-key. Remote execution and salt states will function in the same way as with Salt over ZeroMQ.

Limitations

The 2014.7 release of RAET is not complete! The Syndic and Multi Master have not been completed yet and these are slated for completion in the 2015.5.0 release.

Also, Salt-Raet allows for more control over the client but these hooks have not been implemented yet, thereforre the client still uses the same system as the ZeroMQ client. This means that the extra reliability that RAET exposes has not yet been implemented in the CLI client.

Why?

Customer and User Request

Why make an alternative transport for Salt? There are many reasons, but the primary motivation came from customer requests, many large companies came with requests to run Salt over an alternative transport, the reasoning was varied, from performance and scaling improvements to licensing concerns. These customers have partnered with SaltStack to make RAET a reality.

More Capabilities

RAET has been designed to allow salt to have greater communication capabilities. It has been designed to allow for development into features which out ZeroMQ topologies can't match.

Many of the proposed features are still under development and will be announced as they enter proof of concept phases, but these features include salt-fuse - a filesystem over salt, salt-vt - a parallel api driven shell over the salt transport and many others.

RAET Reliability

RAET is reliable, hence the name (Reliable Asynchronous Event Transport).

The concern posed by some over RAET reliability is based on the fact that RAET uses UDP instead of TCP and UDP does not have built in reliability.

RAET itself implements the needed reliability layers that are not natively present in UDP, this allows RAET to dynamically optimize packet delivery in a way that keeps it both reliable and asynchronous.

RAET and ZeroMQ

When using RAET, ZeroMQ is not required. RAET is a complete networking replacement. It is noteworthy that RAET is not a ZeroMQ replacement in a general sense, the ZeroMQ constructs are not reproduced in RAET, but they are instead implemented in such a way that is specific to Salt's needs.

RAET is primarily an async communication layer over truly async connections, defaulting to UDP. ZeroMQ is over TCP and abstracts async constructs within the socket layer.

Salt is not dropping ZeroMQ support and has no immediate plans to do so.

Encryption

RAET uses Dan Bernstein's NACL encryption libraries and CurveCP handshake. The libnacl python binding binds to both libsodium and tweetnacl to execute the underlying cryptography. This allows us to completely rely on an externally developed cryptography system.