Net::SSH::Multi + Rake == Tasty Potential

Posted by Jamis on April 11, 2008 @ 10:08 AM

Last night I released the first preview of Net::SSH::Multi (gem install --source http://gems.jamisbuck.org net-ssh-multi). Today, let me show you a tasty hint of what you can do with it.

Consider the following Rakefile:

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def remote
  @remote ||= begin
    require 'net/ssh/multi'

    session = Net::SSH::Multi.start

    session.via 'gateway.host', session.default_user

    session.group :web => session.use('web1', 'web2')
    session.group :app => session.use(*(1..8).map { |n| "app%02d" % n })
    session.group :db  => session.use('db1', :properties => { :primary => true })

    session
  end
end

namespace :remote do
  task :hostnames do
    remote.exec("hostname").wait
  end

  task :app_hostnames do
    remote.with(:app).exec("hostname").wait
  end

  task :web_hostnames do
    remote.with(:web).exec("hostname").wait
  end
end

You can now do things like this:

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$ rake remote:hostnames
(in /home/jamis)
[web1] web1.host
[app02] app02.host
[app05] app05.host
[app03] app03.host
[app06] app06.host
[app08] app08.host
[db1] db1.host
[app01] app01.host
[web2] web2.host
[app04] app04.host
[app07] app07.host

The Net::SSH::Multi library is still experimental, but it is stable and full-featured enough that I seriously considered implementing the next release of Capistrano on top of it. (I’ll probably put that off until cap3, though, due to the magnitude of the change.) If you do something cool with it, let me know!

Posted in Tips & Tricks

Comments

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11 Apr 2008

1. Scott Raymond said...

Hey Jamis, that’s cool stuff. I like the idea of using Rake tasks for doing stuff remotely. For the sake of my curiosity, could you explain the benefits/differences between this and the way that Vlad does it? Is there some benefit that Net::SSH::Multi provides that just wrapping the “ssh” command doesn’t? Thanks!

2. Jamis said...

@Scott, I’ve never done more than glance at vlad, so I’m probably the wrong person to ask. Doesn’t shelling out to ssh mean you have to reconnect for every command you want to execute? Net::SSH::Multi opens the connection and caches it, so if you are executing lots of commands in a row you might see better performance. Also, I don’t think vlad works on windows yet…? (As I said, I’m way out of the loop regarding vlad, so that might not be true any more). Net::SSH::Multi is platform independent, as long as OpenSSL and the OpenSSL ruby bindings are installed. At any rate, this isn’t out to replace vlad, or cap. It’s another tool for people to use, is all.

3. Scott Raymond said...

I’m not terribly familiar with Vlad’s internals either, so I don’t know about the connection-caching question. Anyhow, thanks again for the great work on this stuff.

4. Erlend Simonsen said...

Seems like a perfect match for glTail as well. Guess I should start preparing for the next release.

12 Apr 2008

5. Sebastian said...

Nice post, I will try this solution.