Out of many different monitoring solutions, nagios is one of the most used solutions. The following article shall describe in brief, how to set up some useful monitoring tasks:

Defining custom checks

in /etc/nagios4/commands.cfg, you can define a custom command. Let’s do this with a http check, which evaluates the result and checks in this result for a regex:

define command {
 command_name check_http_host_regex
 command_line $USER1$/check_http -H $HOSTADDRESS$ -p $ARG1$ -u $ARG2$ -r $ARG3$ -t30
}

This check is to be called from your /etc/nagios4/$cfg_dir/your_host.cfg:

define service {
 use generic-service
 host_name your.host.name
 service_description nginx_http_result
 is_volatile 0
 notification_options c,r
 check_command check_http_host_regex!80!/foo.css!your_regex
}

After that, you can run nagios4 -v /etc/nagios4/nagios.cfg to verify, that your configuration is valid.