Create cluster_cron.pl

cluster_cron.pl

@@ -0,0 +1,130 @@
+#!/usr/bin/env perl
+use warnings;
+use strict;
+use Sys::Hostname;
+
+# We need a common directory for our nodes to write and read state from plus a couple of cronfiles
+my ($electiondir, $cronfile, $sharedcronfile) = @_;
+
+unless (-d $electiondir) {
+        mkdir $electiondir;
+}
+
+# We need our name
+my $hostname = hostname;
+
+# We also need to know the time
+my $time = time;
+
+
+# Get the nodes in the cluster
+sub get_nodes {
+        # Our data type is a hash with the following fields
+        # name, time, numeric
+        my @nodes = ();
+        my @files = <$electiondir/*>;
+        foreach my $filename (@files) {
+                my $node = {};
+                open(FILE, "<$filename") or die "Could not open file: $!";
+                $filename =~ s/^$electiondir\///;
+                $node->{'name'} = $filename;
+                my $content = <FILE>;
+                chomp $content;
+                $node->{'time'} = $content;
+                $node->{'numeric'} = get_numeric($filename);
+                close FILE;
+                push @nodes, $node;
+        }
+        return @nodes;
+
+
+}
+
+
+# Simply write a unix timestamp to a file with our name on it
+sub write_timestamp {
+        open(FILE,"+>$electiondir/$hostname");
+        print FILE $time;
+        close FILE;
+
+}
+
+# Lets see if we are the active node
+sub is_active {
+
+        my @nodes = @_;
+
+        # Assume you are active
+        my $state = 1;
+        # Loop all nodes
+        foreach my $node (@nodes) {
+                # Dont do anything if this is the node
+                unless ($node eq $node->{'name'}) {
+                        #  If it has been active in the last 120 seconds it is eligable
+                        my $diff = $time - $node->{'time'};
+                        if( $diff < 120 ) {
+                                # Go to passive mode if the numeric of that host is less than that of this host
+                                if( get_numeric($hostname) > $node->{'numeric'} ) {
+                                        $state = 0 ;
+                                }
+                        }
+                }
+        }
+        return $state;
+}
+
+# Turn a hostname in to a decimal number used for comparison, lowest numer gets to be active if it is working
+sub get_numeric {
+        my ($host) = @_;
+        my @ascii = unpack 'C*', $host;
+        my $numeric = '';
+        foreach my $val (@ascii) {
+                $numeric .=  $val;
+        }
+        return $numeric + 0;
+}
+
+# But a # infront of any actime crontab entry 
+sub comment_out {
+        my ($infile, $outfile) = @_;
+        open(INFILE,"<$infile");
+        my $content = '';
+        while(my $line = <INFILE>) {
+                $line =~ s/(^(?!#))/#$1/g;
+                $content .= $line;
+        }
+
+        close INFILE;
+        open(OUTFILE,"+>$outfile");
+        print OUTFILE $content;
+        close OUTFILE;
+
+}
+
+# Remove a # from any crontab entry
+sub uncomment {
+        my ($infile, $outfile) = @_;
+        open(INFILE,"<$infile");
+        my $content = '';
+        while(my $line = <INFILE>) {
+                $line =~ s/^(#)([\d*])/$2/g;
+                $content .= $line;
+        }
+
+        close INFILE;
+        open(OUTFILE,"+>$outfile");
+        print OUTFILE $content;
+        close OUTFILE;
+
+}
+
+# Update timestamp
+write_timestamp;
+
+# See if I am the one
+if (is_active(get_nodes) ){
+        uncomment $sharedcronfile, $cronfile;
+
+} else {
+        comment_out $cronfile, $sharedcronfile;
+}