Sensu: Non Ruby Sensu Plugin

Currently I write all my Sensu plugins in ruby.   Even though I am not a ruby ninja, this has really not been an issue as the plugins I write are typically fairly simple (not to mention there are several already written plugins available see  https://github.com/sensu/sensu-community-plugins/tree/master/plugins [1] )

I do not recommend writing Sensu checks in any other language!  I recommend keeping to Ruby….  But if you have to use another language you can.

I did a few tests with a simple bash script and a simple Scala Script.

Good Resources

I would suggest first going to this post and reading their write up

http://www.programblings.com/2013/11/06/creating-a-sensu-check/ [2]

Bash Script

When Sensu runs a check the exit status of the check will tell Sensu how to handle it.

Exit Status	Sensu handles as
0	OK
1	Warning
2	Critical
3 or more	Unknown

Now for some experimenting.   I am going to make a simple bash script that does not output any text just exits.  (I am going to use the code at http://www.programblings.com/2013/11/06/creating-a-sensu-check/ [2] … tweaking it a little.)

> sudo vi /etc/sensu/plugins/bash_test.sh

#!/bin/bash rand=$RANDOM # 0 to 32,767 if [ $rand -gt 24000 ]; then    exit 0 # OK elif [ $rand -gt 16000 ]; then    exit 1 #Warning elif [ $rand  -gt 8000 ]; then    exit 2 #Critical else    exit 3 #Unknown fi

Make it executable

> sudo chmod u+x /etc/sensu/plugins/bash_test.sh

My Sensu is run by a user named sensu so I need to chown on this file

> sudo chown sensu:sensu /etc/sensu/plugins/bash_test.sh

Now test it.

> sudo ./bash_test.sh

If you run the command by hand you will not see anything.

To get the exit code of the last run command, run this command

> echo $?

Slap the commands together

> sudo ./bash_test.sh; echo $?

Looks like it's working.

Now add a simple check

> sudo vi /etc/sensu/conf.d/check_bash_test.json

Here is my check (of course you will need to change the subscribers to your own).

{   "checks": {     "check_bash_test": {       "command": "/etc/sensu/plugins/bash_test.sh",       "interval": 60,       "occurrences": 1,       "subscribers": [          "check-from-sensu-master"       ]       }     } }

Change the owner (I have a Sensu user)

> sudo chown sensu:sensu /etc/sensu/conf.d/check_bash_test.json

Now restart all my services

> sudo service uchiwa stop && sudo service sensu-server stop && sudo service sensu-api stop && service sensu-client stop     > sudo service sensu-server start && sudo service sensu-api start && service sensu-client start && sudo service uchiwa start

Now tail the log

> sudo tail -f /var/log/sensu/sensu-client.log | grep bash

There it is and it's unknown  = 3

Exit 1

Exit 2

It's working as expected. 

When the status was 0 (OK) the check was resolved.

Now is 3 or more unknown?   Let m update the code to output 11 as a test.

> sudo vi /etc/sensu/plugins/bash_test.sh

#!/bin/bash rand=$RANDOM # 0 to 32,767 if [ $rand -gt 24000 ]; then    exit 0 # OK elif [ $rand -gt 16000 ]; then    exit 1 #Warning elif [ $rand  -gt 8000 ]; then    exit 2 #Critical else    exit 11 #Unknown fi

Yep 11 gets back unknown.

Adding in output

Let me edit the script one more time and add in text output

> sudo vi /etc/sensu/plugins/bash_test.sh

#!/bin/bash rand=$RANDOM # 0 to 32,767 if [ $rand -gt 24000 ]; then    echo "It is OK"    exit 0 # OK elif [ $rand -gt 16000 ]; then    echo "It is Warning"    exit 1 #Warning elif [ $rand  -gt 8000 ]; then    echo "It is Critical"    exit 2 #Critical else    echo "It is Unknown"    exit 11 #Unknown fi

From what I have seen you can also format the output like this

<Class> <Status>: <Message>

#!/bin/bash rand=$RANDOM # 0 to 32,767 if [ $rand -gt 24000 ]; then    echo "BASH_TEST OK: It is OK"    exit 0 # OK elif [ $rand -gt 16000 ]; then    echo "BASH_TEST WARNING: It is Warning"    exit 1 #Warning elif [ $rand  -gt 8000 ]; then    echo "BASH_TEST CRITICAL: It is Critical"    exit 2 #Critical else    echo "BASH_TEST UNKNOWN: It is Unknown"    exit 11 #Unknown fi

I don't see that this format is necessary but it is the standard so why break it J

Write Check in Scala

What about writing a check in scala.

OK first I need to install Scala on my sensu box. 
This is all running on an Ubuntu 14.04 server.

First Install Java 1.7

> sudo apt-get purge openjdk*     > sudo apt-get install python-software-properties     > sudo add-apt-repository ppa:webupd8team/java     > sudo apt-get update     > sudo apt-get install oracle-java7-installer     > java –version

Download scala

> wget http://downloads.typesafe.com/scala/2.11.7/scala-2.11.7.tgz     > tar xf scala-2.11.7.tgz

> sudo mkdir /usr/lib/scala     > sudo mv scala-2.11.7 /usr/lib/scala/     > sudo touch /usr/bin/scala     > sudo ln -fs /usr/lib/scala/scala-2.11.7/bin/scala /usr/bin/scala     > sudo chmod a+x /usr/bin/scala     >  scala -version

Simple Scala Script

> sudo vi /etc/sensu/plugins/scala_test.sh

#!/usr/bin/env scala import scala.util.Random; val rand = new Random().nextInt(4) rand match {   case 0 => println("SCALA_TEST OK: It is OK")   case 1 => println("SCALA_TEST WARNING: It is a Warning")   case 2 => println("SCALA_TEST CRITICAL: It is a Critical")   case _ => println("SCALA_TEST UNKNOWN: It is Unknown") } System.exit(rand)

Make it executable

> chmod u+x /etc/sensu/plugins/scala_test.sh pr

My Sensu is run by a user named sensu so I need to chown on this file

> sudo chown sensu:sensu /etc/sensu/plugins/scala_test.sh

Now test it.

> sudo ./scala_test.sh; echo $?

Seems to be working… now to write a check and restart the Sensu Services.

Now add a simple check

> sudo vi /etc/sensu/conf.d/check_scala_test.json

Here is my check (of course you will need to change the subscribers to your own).

{   "checks": {     "check_scala_test": {       "command": "/etc/sensu/plugins/scala_test.sh",       "interval": 60,       "occurrences": 1,       "subscribers": [          "check-from-sensu-master"       ]       }     } }

Change the owner (I have a Sensu user)

> sudo chown sensu:sensu /etc/sensu/conf.d/check_scala_test.json

Now restart all my services

> sudo service uchiwa stop && sudo service sensu-server stop && sudo service sensu-api stop && service sensu-client stop     > sudo service sensu-server start && sudo service sensu-api start && service sensu-client start && sudo service uchiwa start

Now tail the log

> sudo tail -f /var/log/sensu/sensu-client.log | grep scala

Hey it's working J

In conclusion… It's all about the exit codes J

References

[1]        sensu-community-plugins (git repo)

            https://github.com/sensu/sensu-community-plugins/tree/master/plugins

            Accessed 11/2015

[2]        Creating a Sensu Check

            http://www.programblings.com/2013/11/06/creating-a-sensu-check/

            Accessed 11/2015