Icinga icon   Icinga – How to configure passive checks made easy (2)

In the previous post I explained what is the difference between Icinga active and passive checks, why can be interesting to use passive checks, what is the result format Icinga is expecting when processing those checks and the way I use to send those results (instead of using snmp traps).

Now it is time to show how to configure it and examples

Enable passive checks

Enable the command feature by running…

icinga2 feature enable command

… and dont forget to restart

service icinga2 restart

Now it can be checked that the external command file has been created:

# ls /var/run/icinga2/cmd/icinga2.cmd -l
prw-rw---- 1 nagios www-data 0 Nov 24 09:13 /var/run/icinga2/cmd/icinga2.cmd

I remind you that the external command file is where the passive check results strings should be placed to allow Icinga process them.

Create a passive check

Configure a template (/etc/icinga2/conf.d/templates.conf)…

template Service "passive-service" {
  import "generic-service"
  check_command = "passive"
  enable_active_checks = false
  enable_passive_checks = true
  check_interval = 2m

(Visit this post Understanding checks and notification types for more details)

… and a service that uses the template (/etc/icinga2/conf.d/services.conf)

apply Service "TEST service" {
  import "passive-service"
  assign where host.name == "TEST-SERVER"

(of course, SERVER1 should be an already configured host)

Reload your icinga server to apply the changes so you can see the recently created service:

Configure passive checks in Icinga

Now, as we saw in the previous post, this is the format in which the service results should be sent:

[<timestamp>] PROCESS_SERVICE_CHECK_RESULT;<host_name>;<svc_description>;<return_code>;<plugin_output>

So, as a test, lets try sending results manually to the external command file. For example, this should set the service in “OK” state:

# echo "[`date +%s`] PROCESS_SERVICE_CHECK_RESULT;TEST-SERVER;TEST service;0;OK result sent manually" >> /var/run/icinga2/cmd/icinga2.cmd

Some seconds after running the command…

Configure passive checks in Icinga

For “WARNING” state:

# echo "[`date +%s`] PROCESS_SERVICE_CHECK_RESULT;TEST-SERVER;TEST service;1;WARNING result sent manually" >> /var/run/icinga2/cmd/icinga2.cmd

Configure passive checks in Icinga

Finally, “CRITICAL” state:

# echo "[`date +%s`] PROCESS_SERVICE_CHECK_RESULT;TEST-SERVER;TEST service;2;Uffff CRITICAL result sent manually" >> /var/run/icinga2/cmd/icinga2.cmd

Configure passive checks in Icinga

Ok, it’s working. But this seems not to be very useful because we are sending the results from the icinga server itself. But the goal is to send results collected in a external system. To allow that, we need toto…

Configure tcp listener daemon

This daemon will be listening in certain port of the Icinga server waiting to receive results that will redirect to the external command file.

Install tcpserver utility

I have used “tcpserver”. It listens for incoming TCP connections and runs a program in response to a connection. In debian you can install it comes with the package ucspi-tcp

# apt-get install icspi-tcp

Create script to redirect incoming results

The idea is, for each connection, redirecting the data sent to the external command file. So let’s create the script that we will associate with the listener (for example, /usr/scripts/remote-command.sh) :


echo $MESSAGE >> /var/run/icinga2/cmd/icinga2.cmd

Configure tcpserver daemon to be run at startup

Now this script has been created, it can be used with the tcpserver utility this way:

nohup tcpserver -q -H -R <PORT> <SCRIPT> &> /dev/null &

nohup tcpserver -q -H -R 3334 /usr/scripts/remote-commands.sh &> /dev/null &

(nohup and the ending & is to launch it in background). After running the command, you can use a simple telnet or netcat to connect to the port (i have chosen 3334, but you use any port you want), and all you write will be redirected to the external command file because is processed by the script.

But, you want the tcpserver daemon to be launched automatically when you init the system, so lets create the /etc/init.d/remote-commands-daemon.sh script:


# Provides:       remote-commands-daemon
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: service to receive icinga remote external commands

case "$1" in
    if [ -f $LOCK_FILE ]
        echo "Service already running..."
        echo "Starting service remote-commands "
        nohup tcpserver -q -H -R 3334 /usr/scripts/remote-commands.sh &>/dev/null &
        touch $LOCK_FILE
    if [ ! -f $LOCK_FILE ]
        echo "Service is not running..."
        echo "Stopping service remote-commands"
        killall -9 tcpserver
        rm $LOCK_FILE
    echo "Usage: /etc/init.d/remote-command-daemon {start|stop}"
    exit 1

exit 0

And create the related symlinks:

# update-rc.d remote-commands-daemon.sh defaults

From now, when booting up the system the daemon will be automatically started.
Or you can manually start/stop it:

# /etc/init.d/remote-commands-daemon.sh <start | stop>

Script that checks and sends results remotely

Now the icinga server is listening in the configured port for incoming check result strings, lets suppose we want monitor the number of processes a system is running.

This powershell example could be used in a windows system:



$DATETIMESTAMP = (Get-Date).ToUniversalTime()
$DATETIMESTAMP = "[{0:G}]" -f [int][double]::Parse($DATETIMESTAMP)

$RESULT = (Get-Process | Measure).Count

    $MSGTMP = " PROCESS_SERVICE_CHECK_RESULT;TEST-SERVER;Test service;2;There are $RESULT processes running"
        $MSGTMP = " PROCESS_SERVICE_CHECK_RESULT;TEST-SERVER;Test service;1;There are $RESULT processes running"
        $MSGTMP = " PROCESS_SERVICE_CHECK_RESULT;TEST-SERVER;TEST service;0;There are $RESULT processes running"



Note that the timestamp is calculated because it is needed to be included in the result string.
To send string via TCP/IP i use the windows version of the netcat tool by piping the result string to it.

Configure passive checks in Icinga

Schedule the execution of this script (the configuration is not in the scope of this post) so you can keep the service monitored.

Raise alert if no results are being sent

Icinga can be configured to raise an alert If for any reason the external system is not sending the monitoring results (visit this post Understanding checks and notification types for more details).

Send performance data

If you are generating graphs of the active services, you can also generate of the passive ones the same way. Simply add the performance data in your monitoring script.

[<timestamp>] PROCESS_SERVICE_CHECK_RESULT;<host_name>;<svc_description>;<return_code>;<plugin_output>|<metric>=<value>;;;

For example, in the previous script:

if ($RESULT -gt 300)
    $MSGTMP = " PROCESS_SERVICE_CHECK_RESULT;TEST-SERVER;Test service;2;There are $RESULT processes running|num=$RESULT;;;"
    if ($RESULT -gt 200)
        $MSGTMP = " PROCESS_SERVICE_CHECK_RESULT;TEST-SERVER;Test service;1;There are $RESULT processes running|num=$RESULT;;;"
        $MSGTMP = " PROCESS_SERVICE_CHECK_RESULT;TEST-SERVER;TEST service;0;There are $RESULT processes running|num=$RESULT;;;"

Configure passive checks in Icinga

All the configurations explained in this post are not as hard as it appears to be, and once you have done it for the first passive service the following are very fast to create.  🙂


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