Perl & Bash scripts to warn you if your website is failing

check_server.sh

#!/bin/bash

# Actual recipient and sender are defined in another file
script_dir=`dirname $0`;
script_name=`basename $0`;
config_file="$script_dir/config-$script_name";

if [ -f $config_file ]; then
	source $config_file;
else
	# Vars for testing purpose
	SENDMAIL=/usr/sbin/sendmail
	URL=www.example.com
	EXPECTED=403 # Be sure to test this ;)
	RECIPIENT=a.dotreppe@aspyct.org; # Set this to your email address
	SENDER=debug@aspyct.org;
fi;

test_url.pl $URL $EXPECTED --quiet
status_code=$?

if [ $? ]; then
	echo "Server not responding as expected" >&2
	echo "Sending alert mail to $RECIPIENT from $SENDER";

	tmpfile=`mktemp`;
	echo "From: $SENDER" >> $tmpfile;
	echo "To: $RECIPIENT" >> $tmpfile;
	echo "Subject: $URL down" >> $tmpfile;
	echo "" >> $tmpfile;
	echo "The server check returned $status_code" >> $tmpfile;
	echo "We were expecting $EXPECTED" >> $tmpfile;
	
	$SENDMAIL -t < $tmpfile;
	rm $tmpfile;
fi;

test_url.pl

#!/usr/bin/env perl

use strict;
use Switch;
use Getopt::Long;

# Parameters
my $expected = 200;
my $url;
my $quiet = 0;

my $result = GetOptions("quiet" => \$quiet);

if ($quiet) {
	open STDERR,'>/dev/null';
}

my $argcount = @ARGV;

switch ($argcount) {
	case 2 {
		$expected = $ARGV[1];
		next
	}
	case [1..2] {
		$url = $ARGV[0];
	}
}

if (!defined $url || $url eq "help") {
	print "Usage: $0 <url to test> [<expected return code> [--quiet]]\n";

	if ($url == undef) {
		exit 1;
	}
}

my @headers = `curl -sIL $ARGV[0]`;

if (@headers == 0) {
	print STDERR "No return headers\n";
	exit 2;
}

my $status = $headers[0];
if ($status =~ /^http\/\d\.\d +(\d+)/i) {
	my $code = $1;

	if ($code ne $expected) {
		print STDERR "Got $code, expected $expected\n";
		
		if ($code) {
			exit $code;
		}
		else {
			exit 3;
		}
	}
}

Copy this gist to your perl-enabled server and run it with a cron job :) You should maybe even wrap it in another script to send you a mail/text message if the check fails.

Usage:
Want a 200 ? ./test_url.pl www.aspyct.org
Want a 403 ? ./test_url.pl www.aspyct.org 403
No error message ? ./test_url.pl --quiet ...

Or, for a more elaborate solution, you could also look into Prometheus (https://prometheus.io) and its Blackbox Exporter (https://github.com/prometheus/blackbox_exporter)