JohnAllen.us

First off, let me say that there is not an original thought in any of this code, since it has all been taken from a number of different articles out on the Internet. The Daemonizing code was taken from the Active State Code Recipes area.

One of my customers has a number of database servers that we would like to monitor and see what the state of the clusters are. The problem is that the clustat command — that used to be run-able by everyone in a lesser version of RHEL — is now only usable by root in RHEL v5.3!. Not wanting to give out root access to everyone, we decided that a quick little custom server that provided the output of the clustat command in XML format would do the trick. Then I just wrote a Ruby program to query all the Clustat XML servers and display the results in a readable format. If there is enough interest, I can post a public version of that program.

Here’s the code:

import sys
import os
import subprocess
import SocketServer
from socket import *
import fcntl
import struct

class CluStatHandler(SocketServer.BaseRequestHandler) :

   def handle(self) :
     p = subprocess.Popen(['clustat', '-x'], stdout=subprocess.PIPE)
     out, err = p.communicate()
     self.request.send(out)

def get_ip_address(ifname):

	s = socket(AF_INET, SOCK_STREAM)
	return inet_ntoa(fcntl.ioctl(s.fileno(), 0x8915, struct.pack('256s', ifname[:15]))[20:24])

def main():

   HOST = get_ip_address('bond5')
   PORT = 2113

   server = SocketServer.TCPServer((HOST, PORT), CluStatHandler)
   server.serve_forever()

if __name__ == "__main__" :
   try:
        pid = os.fork()
        if pid > 0:
            # exit first parent
            sys.exit(0)
   except OSError, e:
        print >>sys.stderr, "fork #1 failed: %d (%s)" % (e.errno, e.strerror)
        sys.exit(1)

   # decouple from parent environment
   os.chdir("/")
   os.setsid()
   os.umask(0) 

   # do second fork
   try:
       pid = os.fork()
       if pid > 0:
           # exit from second parent, print eventual PID before
           print "Daemon PID %d" % pid
           sys.exit(0)
   except OSError, e:
       print >>sys.stderr, "fork #2 failed: %d (%s)" % (e.errno, e.strerror)
       sys.exit(1) 

   # start the daemon main loop
   main() 

The main() function sets up the SocketServer, which in turn calls the Handler to go run the clustat command in XML mode (the ‘-x’ parameter), and return the output. Since the servers that my customer has includes several network interfaces, I also had to figure out a way to start the server on the right interface. The get_ip_address function opens a socket on the specified interface, and then queries for its IP address.

A very handy tool to have in your bag of tricks!