Writing plugins to wrap a command in mcollective is very easy.
What is difficult is figuring out all of the conventions that you need to follow.
I’m going to walk you through an example with some tips.
Conventions you need to follow
1) Agents need to go in the agent directory. You can find it with the following command
sudo find / -name rpcutil.ddl -exec dirname {} \;
2) The file name should be all lowercase with a file mode of 644
test@mcollectivemaster:/usr/share/mcollective/plugins/mcollective/agent$ ls -l wrapit.rb
-rw-r--r-- 1 root root 1127 2012-04-13 19:05 wrapit.rb
3) The class name needs to match the file name with at least the first letter capitalized.
4) To more easily debug make sure the following two lines are present in your /etc/mcollective/server.cfg so you can find errors in syslog
logger_type = syslog
loglevel = debug
5) Restart mcollective between changes to the agent file
An example agent
module MCollective
module Agent
class Wrapit < RPC::Agent
###################################################################
metadata :name => "My Agent",
:description => "Example of how to wrap a command",
:author => "Me <me@example.com>",
:license => "DWYWI",
:version => "0.1",
:url => "http://blog.mague.com",
:timeout => 10
###################################################################
#functions
def run_command(cmd)
cmdrun = IO.popen(cmd)
output = cmdrun.read
cmdrun.close
if $?.to_i > 0
logger.error "WRAPIT: #{cmd}: #{output}"
reply.fail! "ERROR: failed with #{output}"
end
output
end
###################################################################
#actions
action "ping" do
reply[:info] = run_command("/bin/ping -c 5 #{request[:target]}")
end
###################################################################
end #class
end #agent
end #moduleMcollective uses the request data structure to receive information from the client and reply to send information back to the client. The actions are methods that the client calls to run.
When running commands be sure to wrap with IO.popen so that you can capture both the output and pass the error code. Do not forget to close the popen or you will leak file handles and cause trouble.
An Example Client
#!/usr/bin/env ruby
require 'rubygems' if RUBY_VERSION < "1.9"
require 'mcollective'
include MCollective::RPC
args = {}
action=""
options = rpcoptions do |parser, options|
parser.on('-K', '--targ TARGET', 'Target to test against') do |v|
args[:target] = v
end
parser.on('-S', '--action ACTION', 'action') do |v|
action = v
end
end
mc = rpcclient("wrapit", :options => options)
#mc.fact_filter "servertype", "/myservertype/"
mc.timeout = 10
mc.progress = false
mc.send(action, args).each do |resp|
if resp[:statusmsg] == "OK"
puts resp[:sender]
puts resp[:data][:info]
else
puts "ERROR:"
p resp
end
endThe RPC includes all kinds of switches so be sure to run your script with -h to make sure none of your arguments overlap as they will be overwritten by the default switches.
You can add your own fact_filters and turn off the progress bar which is useful with web interfaces.
Be sure to check the statusmsg sent back from the agent, so you can catch any errors.
Since developer access is limited in my work environment, I wrote lots of customer agents to allow troubleshooting and deployment to be coordinated. Putting them behind a Sinatra web front end has made life easier for all.
Update:It was kindly pointed out to me by R.I. Pienaar that instead of using popen, there is a built-in run() function that is even more flexible.
cmd_output = []
cmd_error = ""
run ( "/bin/ping -c #{request[:target}",
:environment => {"MYSETTING" => "ABC123"}
:cwd => "/home/testguy",
:stdout => cmd_output,
:sdterr => cmd_error,
)
