nagios-npre-client.md

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Nagios NRPE client

Let's be very clear. There are components to monitoring. It's not difficult but can be confusing if not clearly communicated from the outset.

1. Central Server: we are using icinga 2 for the core and icinga web for the GUI (version 2 of the web interface is still under "heavy development")
2. Clients: Any server we want to monitor will be monitored in one of two ways:
   1. The central server uses ping, http or other commands to execute against the targeted device. No modules are installed on the targeted device.
   2. Install a client module on the remote device, which can then communicate with Icinga2
      • On Linux, install Nagios Remote Plugin Executor (NRPE) on the remote Linux device.
      • On Windows, install NSClient++ NRPE service on the remote Windows device.

The example below covers setting up NRPE on Ubuntu 14.04. For help on installing NSClient++ on Windows see this Windows 8.1 example.

To have this example work fully, a Central Server installation is required. See here for help on setting up an Icinga2 Central Server.

Install NRPE on Ubuntu Linux 14.04

On an Ubuntu 14.04 installation, I configured the ip to be 192.168.1.20 and the hostname to be ub14-henry.

Install the NRPE packages.

$ sudo apt-get install nagios-plugins nagios-nrpe-server

Get the name of root filesystem because we will enter that in the NRPE config file next. My filesystem is /dev/vda1.

$ df -h /

#OUTPUT
Filesystem      Size  Used Avail Use% Mounted on
/dev/vda1        18G  4.4G   13G  27% /

Open the NRPE config file.

$ sudo vim /etc/nagios/nrpe.cfg

Edit as follows:

# Change the server address to the private local ip of the server. 
server_address=192.168.1.20

# Tell this NRPE that it is okay for the ip address of the Icinga2 Central Server to connect to it
allowed_hosts=192.168.1.3

# Change /dev/hda1 to my root filesystem name, /dev/vda1
command[check_hda1]=/usr/lib/nagios/plugins/check_disk -w 20% -c 10% -p /dev/vda1

Restart NRPE.

$ sudo service nagios-nrpe-server restart

---

In the nrpe.cfg file, notice commands that were commented in, such as:

command[check_users]=/usr/lib/nagios/plugins/check_users -w 5 -c 10
command[check_load]=/usr/lib/nagios/plugins/check_load -w 15,10,5 -c 30,25,20
command[check_hda1]=/usr/lib/nagios/plugins/check_disk -w 20% -c 10% -p /dev/vda1
command[check_zombie_procs]=/usr/lib/nagios/plugins/check_procs -w 5 -c 10 -s Z
command[check_total_procs]=/usr/lib/nagios/plugins/check_procs -w 150 -c 200 

check_users, check_load, check_hda1, check_zombie_procs and check_total_procs are the names of command that can be associated with check_nrpe when we configure that Icinga2 Central Server service.

But on the client, test if this command works.

$ sudo /usr/lib/nagios/plugins/check_disk -w 20% -c 10% -p /dev/vda1
DISK OK - free space: / 12628 MB (73% inode=81%);| /=4448MB;14410;16211;0;18013
avatar@ub14-henry:~$ sudo vim /etc/nagios/nrpe.cfg

Icinga2 Central Server

Back on the Icinga2 Central Server, we need to install the Nagios check_nrpe plugin. Using --no-install-recommends installs the plugin only and not the extra nagios3-related libraries.

$ sudo apt-get --no-install-recommends install nagios-nrpe-plugin

Open commands.conf.

$ sudo vim /etc/icinga2/conf.d/commands.conf 

Add a new CheckCommand, giving it the name check_nrpe.

object CheckCommand "check_nrpe" {
  import "plugin-check-command"

  command = [
    PluginDir + "/check_nrpe",
    "-H", "$address$",
    "-c", "$remote_nrpe_command$",
  ]
}

Create a config file for the new host.

$ sudo vim /etc/icinga2/conf.d/hosts/ub41-henry.conf

The full file looks like this - note the embedded comments, explaining what each section does.

// defines the Host as "ub14-henry" as residing at ip address "192.168.1.20"
object Host "ub14-henry" {
  import "generic-host"

  address = "192.168.1.20"
  check_command = "hostalive"

  vars.lan = "example.com"
}

// The ping4 command is initiated by the Icinga2 Central Server and pings the targeted host, ub14-henry
object Service "ping4" {
  import "generic-service"

  host_name = "ub14-henry"
  check_command = "ping4"
}

// This services uses "check_nrpe" to connect to port 5666 of the targeted "ub14-henry" hosts and has it execute the "check_users" command
object Service "users" {
  import "generic-service"

  host_name = "ub14-henry"

  check_command = "check_nrpe"
  vars.remote_nrpe_command = "check_users"
}

// This services uses "check_nrpe" to connect to port 5666 of the targeted "ub14-henry" hosts and has it execute the "check_load" command
object Service "load" {
  import "generic-service"

  host_name = "ub14-henry"
  check_command = "check_nrpe"
  vars.remote_nrpe_command = "check_load"
}

// This services uses "check_nrpe" to connect to port 5666 of the targeted "ub14-henry" hosts and has it execute the "check_hda1" command
object Service "disk" {
  import "generic-service"

  host_name = "ub14-henry"
  check_command = "check_nrpe"
  vars.remote_nrpe_command = "check_hda1"
}

Check that configuration syntax is correct.

$ sudo service icinga2 checkconfig

Restart Icinga2.

$ sudo service icinga2 restart

Go to the Icinga-Web interface and refresh it. The nrpe checks should be pending and eventually will be successful or fail.