Add fail2ban CheckCommand definition

The check_fail2ban plugin use the fail2ban-client binary
to monitor fail2ban jails.

doc/10-icinga-template-library.md

@@ -2993,6 +2993,33 @@ lsyncd_statfile         | **Optional.** Set status file path (default: /var/run/
 lsyncd_warning          | **Optional.** Warning if more than N delays (default: 10).
 lsyncd_critical         | **Optional.** Critical if more then N delays (default: 100).
 
+#### fail2ban <a id="plugin-contrib-command-fail2ban"></a>
+
+The [check_fail2ban](https://github.com/fail2ban/fail2ban/tree/master/files/nagios) plugin
+uses the `fail2ban-client` binary to monitor [fail2ban](http://www.fail2ban.org) jails.
+
+The plugin requires `sudo` permissions.
+You can add a sudoers file to allow your monitoring user to use the plugin, i.e. edit /etc/sudoers.d/icinga and add:
+```
+icinga ALL=(root) NOPASSWD:/usr/lib/nagios/plugins/check_fail2ban
+```
+
+and set the correct permissions:
+```bash
+chown -c root: /etc/sudoers.d/icinga
+chmod -c 0440 /etc/sudoers.d/icinga
+```
+
+Custom attributes passed as [command parameters](03-monitoring-basics.md#command-passing-parameters):
+
+Name                    | Description
+------------------------|---------------------------------------------------------------------------
+fail2ban_display        | **Optional.** To modify the output display, default is 'CHECK FAIL2BAN ACTIVITY'
+fail2ban_path           | **Optional.** Specify the path to the tw_cli binary, default value is /usr/bin/fail2ban-client
+fail2ban_warning        | **Optional.** Specify a warning threshold, default is 1
+fail2ban_critical       | **Optional.** Specify a critical threshold, default is 2
+fail2ban_socket         | **Optional.** Specify a socket path, default is unset
+fail2ban_perfdata       | **Optional.** If set to true, activate the perfdata output, default value for the plugin is set to true.
 
 ### Operating System <a id="plugin-contrib-operating-system"></a>
 

itl/plugins-contrib.d/network-services.conf

@@ -101,3 +101,36 @@ object CheckCommand "lsyncd" {
 		}
 	}
 }
+
+object CheckCommand "fail2ban" {
+	command = [ "sudo", PluginDir + "/check_fail2ban" ]
+
+	arguments = {
+		"-D" = {
+			value = "$fail2ban_display$"
+			description = "To modify the output display, default is 'CHECK FAIL2BAN ACTIVITY'"
+		}
+		"-P" = {
+			value = "$fail2ban_path$"
+			description = "Specify the path to the tw_cli binary, default value is /usr/bin/fail2ban-client"
+		}
+		"-w" = {
+			value = "$fail2ban_warning$"
+			description = "Specify a warning threshold, default is 1"
+		}
+		"-c" = {
+			value = "$fail2ban_critical$"
+			description = "Specify a critical threshold, default is 2"
+		}
+		"-s" = {
+			value = "$fail2ban_socket$"
+			description = "Specify a socket path, default is unset"
+		}
+		"-p" = {
+			set_if = "$fail2ban_perfdata$"
+			description = "If set to true, activate the perfdata output"
+		}
+	}
+
+	vars.fail2ban_perfdata = true
+}