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I have a rails app that needs to communicate with a couple of servers through ssh. I'm using the Net::SSH library and it works great. I would like however to be able to cache/store the ssh connections somehow between requests (something like OpenSSH multiplexing).

So, i can't store them in a key-value store like Memcached or Redis (because ssh connections are not serializable).

I don't want to store them in a session because they are meant to be used by all users (and besides i think it needs to be serializable also).

I managed to get this working with class variables and initiliazer constants. I know that class variables don't replicate between servers (in production), and i'm pretty certain initializer constants also don't. Something like:

initializer:

SSH = {}

model:

class Server
    def connection
        require 'net/ssh'
        SSH[name] ||= Net::SSH.start(ip, "root", :password => password)
    end
end

OpenSSH multiplexing would be great but i'm not sure if i could do that through the Net::SSH ruby library (i'm back to storing the master connection somewhere).

Are there any other solutions? Or if not, which one is the least evil of them all?

alexcepoi
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2 Answers2

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Perhaps rather than trying to share sockets across requests which is bound to end up causing pain and suffering you could delegate to a background processor of some kind? You could set up an ssh tunnel and use DRb to talk across it as if it was just a local network daemon, or any of the large number of networked asynchronous job handling daemons.

http://ruby-toolbox.com/categories/queueing.html

noodl
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  • Redis + resque was another idea that crossed my mind, but i was unsure how to implement it. So what you are saying is to start a background process which creates the ssh connection and acts as daemon... And send all requests to it through say, resque. Did i get you correctly? Sorry for being too noobish i don't know much about these background queue managers... – alexcepoi Jan 22 '11 at 02:46
  • It's hard to give a concrete answer without knowing what you're going to use the ssh connection for. If you're attempting to run shell commands on another machine originating from web requests, it might be that you'd be better off queueing tasks in one of the daemons listed. That way you're not at the mercy of network latency during your request handling. – noodl Jan 22 '11 at 18:14
  • yes all shell commands are originating from web requests and network latency is my primary concern. I also need status reporting but from my very limited research i think that should be possible.. – alexcepoi Jan 22 '11 at 18:24
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To keep the SSH connection up between requests, you'll need to spawn off a background process. The background process can open up a pipe or some other sort of interprocess communication method, the handle to which you can store in a serializable way.

Note that this is a non-trivial exercise, which is why I've only described it at high-level detail.

Andy Lindeman
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  • Really? I thought all IO connections are unserializable (so ipc also). At any rate it seems that a background process to handle my ssh connection is the best way to go. Just need to figure out what gems/libraries i should use.. Any suggestions? – alexcepoi Jan 22 '11 at 02:57