Using Nagios and NRPE to monitor remote hosts

We have setup Nagios to monitor our localhost centos, but how to monitor remote hosts? We can monitor remote hosts using SNMP or NRPE
In our testing environment, we will setup Nagios to monitor host centos-1 and centos-2 using NRPE.
To use NRPE, we need to install NRPE on both monitoring host and remote hosts:

Steps to setup remote hosts for NRPE monitoring:
1. Download nagios-plugins-1.4.16.tar.gz, nrpe-2.14.tar.gz
2. Create account for NRPE service

# useradd nagios
# passwd nagios

3. Install nagios-plugs

# tar zxpf nagios-plugins-1.4.16.tar.gz
# cd nagios-plugins-1.4.16
# ./configure --with-nagios-user=nagios \
  --with-nagios-group=nagios
# make
# make install
# chown nagios:nagios /usr/local/nagios

4. Install NRPE

# tar zxpf nrpe-2.14.tar.gz
# cd nrpe-2.14
# ./configure
# make all
# make install-plugin
# make install-daemon
# make install-daemon-config

5. Modify /usr/local/nagios/etc/nrpe.cfg to allow host centos(192.168.100.100) to connect to NRPE

allowed_hosts=127.0.0.1,192.168.100.100

6. Start NRPE, enable autostart to NRPE

# /usr/local/nagios/bin/nrpe -c \
  /usr/local/nagios/etc/nrpe.cfg -d
# echo '/usr/local/nagios/bin/nrpe -c \
  /usr/local/nagios/etc/nrpe.cfg -d' >> /etc/rc.local

7. Verify NRPE is working properly

# /usr/local/nagios/libexec/check_nrpe -H localhost
NRPE v2.14

Steps to setup monitoring host for NRPE monitoring
1. Download nrpe-2.14.tar.gz
2. Install NRPE

# tar -zxpf nrpe-2.14.tar.gz
# cd nrpe-2.14
# ./configure
# make all
# make install-plugin

3. Enable monitoring of centos-1
Update /usr/local/nagios/etc/objects/commands.cfg to enable command check_nrpe

# ‘check_nrpe’ command definition
define command{
        command_name check_nrpe
        command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -t 30 -c $ARG1$
}

update /usr/local/nagios/etc/nagios.cfg to include this line

cfg_file=/usr/local/nagios/etc/objects/centos-1.cfg

4. Edit /usr/local/nagios/etc/objects/centos-1.cfg

define host{
        use                 linux-server
        host_name           centos-1
        alias               centos-1
        address             192.168.100.101
        }


define hostgroup{
        hostgroup_name      centos
        alias               centos
        members             centos-1
        }


define service{
        use                 generic-service
        host_name           centos-1
        service_description PING
        check_command       check_ping!100.0,20%!500.0,60%
        }

define service{
        use                 generic-service
        host_name           centos-1
        service_description Server Load
        check_command       check_nrpe!check_load
        }

define service{
        use                 generic-service
        host_name           centos-1
        service_description /rhiso Usage
        check_command       check_nrpe!check_rhiso
        }

5. Restart Nagios service

# service nagios restart

Steps to enable nrpe commands check_load and check_rhiso on remote host centos-1
Edit /usr/local/nagios/etc/nrpe.cfg, add these 2 lines:

command[check_load]=/usr/local/nagios/libexec/check_load -w 15,10,5 -c 30,25,20
command[check_rhiso]=/usr/local/nagios/libexec/check_disk -w 20% -c 10% /rhiso

restart nrpe daemon

# pkill nrpe
# /usr/local/nagios/bin/nrpe -c \
  /usr/local/nagios/etc/nrpe.cfg -d

Login to http://centos/nagios again, you will see now we have host centos-1 monitored, similarly we can setup the monitoring of centos-2