Nagios

Install Client

apt-get install nagios-nrpe-server nagios-plugins-basic -y

Client Important Files

/etc/nagios/nrpe.cfg           <- allowed_hosts of server goes here
/usr/lib/nagios/plugins 	<- specific checks go here

Server Important Files

/usr/lib/nagios/plugins		<- nothing important here, actually
/etc/nagios3/config.d                  <- everything goes here

Nagios Config

• make sure IPs, ports, security groups allow communication
• client: in /etc/nagios/nrpe.cfg:

allowed_hosts <should include the server ip>
command[echo_ok3]=/usr/lib/nagios/plugins/echo_ok3

• client: restart service

sudo kill -9 `ps aux | grep nr | grep -v color | awk '{print $2}'` ; /usr/sbin/nrpe -c /etc/nagios/nrpe.cfg -d 

• server:

define command {
  command_name echo-ok3
  command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c echo_ok3
}
define service {
  service_description echo-ok3
  hostgroup_name microsites3_api
  check_command echo-ok3
  use default-service
}

Nagios Utils

Setup Client

apt-get install -y nagios-plugins nagios-nrpe-server

Change password

htpasswd -c -b  /etc/nagios/htpasswd.users nagiosadmin admin

Nagios Custom Plugin

CHECK_NRPE: Error – Could not complete SSL handshake

From: https://geekpeek.net/could-not-complete-ssl-handshake/