Forking Ruby Processes

For todays adventure in Ruby, I’m going to be writing a simple daemon process. To start with this daemon won’t do anything too useful – every 1 second it’ll print the time to STDOUT.

Once we have that working I’m going to use the code I created previously to check that a socket is open and increase the period to 15 seconds.

First, the time process.

kawaii:~ craig$ irb
irb(main):001:0> fork do # Fork a new process
irb(main):002:1*   while true # Loop forever
irb(main):003:2>     puts Time.now # Print the time
irb(main):004:2>     sleep 1 # Sleep for a second
irb(main):005:2>   end # while true
irb(main):006:1> end # fork
=> 15738
irb(main):007:0> Sat Jun 03 11:31:09 BST 2006
Sat Jun 03 11:31:10 BST 2006
Sat Jun 03 11:31:11 BST 2006

Voilà. Easy.

Next, we check for an open socket. For this I’ll check that Postfix is listening on port 25 for mail on the secondary MX, mx2.xeriom.net. We need to remember to include the socket library or we’ll always hit the rescue block (oops!)

irb(main):045:0> require 'socket'
=> true
irb(main):046:0> fork do
irb(main):047:1*   while true
irb(main):048:2>     begin
irb(main):049:3*       t = TCPSocket.open('mx2.xeriom.net', 'smtp')
irb(main):050:3>       puts Time.now.to_s + ": MX2 is listening on port 25."
irb(main):051:3>       t.close
irb(main):052:3>     rescue
irb(main):053:3>       puts Time.now.to_s + ": MX2 is NOT listening on port 25."
irb(main):054:3>     end
irb(main):055:2>     sleep 15
irb(main):056:2>   end
irb(main):057:1> end
=> 15759
irb(main):058:0> Sat Jun 03 11:48:25 BST 2006: MX2 is listening on port 25.
Sat Jun 03 11:48:41 BST 2006: MX2 is listening on port 25.
Sat Jun 03 11:48:56 BST 2006: MX2 is NOT listening on port 25.
Sat Jun 03 11:49:11 BST 2006: MX2 is listening on port 25.

Okay, that was a little too easy… How about we extend the problem: This time, let’s check an arbitrary number of sockets on an arbitrary number of hosts.

irb(main):107:0> host_sockets = { 'mx2.xeriom.net' => [ 25 ], 'kiwi.xeriom.net' => [ 21, 22, 25 ], 'guava.xeriom.net' => [ 21, 22, 25 ], 'mx1.xeriom.net' => [ 25 ] }
=> {'mx2.xeriom.net' => [ 25 ], 'kiwi.xeriom.net' => [ 21, 22, 25 ], 'guava.xeriom.net' => [ 21, 22, 25 ], 'mx1.xeriom.net' => [ 25 ]}
irb(main):108:0> fork do
irb(main):109:1*   while true
irb(main):110:2>     host_sockets.each { |hostname, sockets|
irb(main):111:3*       Thread.new(hostname, sockets) { |host, socks|
irb(main):112:4*         socks.each { |socket|
irb(main):113:5*           begin
irb(main):114:6*             t = TCPSocket.new(host, socket)
irb(main):115:6>             puts Time.now.to_s + ": " + host.to_s + " is listening on port " + socket.to_s
irb(main):116:6>             t.close
irb(main):117:6>           rescue
irb(main):118:6>             puts Time.now.to_s + ": " + host.to_s + " is NOT listening on port " + socket.to_s
irb(main):119:6>           end
irb(main):120:5>         }
irb(main):121:4>       }
irb(main):122:3>     }
irb(main):123:2>     sleep 15
irb(main):124:2>   end
irb(main):125:1> end
=> 15784
Sat Jun 03 12:16:56 BST 2006: kiwi.xeriom.net is listening on port 21Sat Jun 03 12:16:56 BST 2006: mx2.xeriom.net is listening on port 22

Sat Jun 03 12:16:56 BST 2006: guava.xeriom.net is listening on port 22
Sat Jun 03 12:16:56 BST 2006: kiwi.xeriom.net is listening on port 22Sat Jun 03 12:16:56 BST 2006: mx2.xeriom.net is listening on port 25

Sat Jun 03 12:16:56 BST 2006: kiwi.xeriom.net is listening on port 25Sat Jun 03 12:16:56 BST 2006: guava.xeriom.net is listening on port 25 ...

Obviously I’d need to think about the architecture of this code if I was going to extend it to many millions of hosts – a thread for each host would have a lot of overhead – but for a small network it’s fine as it is.

written by

Craig

published

2011-03-03