Varnish is a web application accelerator and sits in front of your web server. It speeds up your application by caching some, if not all of the content meaning it reduces the load on your web server and can reduce the load on you backend as less lookups will be needed by the frontend.
As varnish is the first thing users hit it is imperative it is working properly and you have statistics on how it is performing. This plugin can give you a better insight into how affectively varnish is running and tell you if its having problems.
https://github.com/thomasweaver/check_varnishInstall
To use this plugin you need to have varnishstat installed which is installed by default when you install varnish.
Perl is also required for this plugin. If you don’t have Perl installed you can install in by running the command below
sudo apt-get install perl
or
sudo yum install perl
Now you can clone the repo above
git clone https://github.com/thomasweaver/check_varnish.git
Now you should have a file “check_varnish.pl” make sure that it has execute permissions:
chmod u+x check_varnish.pl
You now need to copy this file to your nagios plugins folder. You should consult your nagios config to find out where this is. Mine was ‘/usr/lib/nagios/plugin’
mv check_varnish.pl /usr/lib/nagios/plugins/.
How To
check_varnish.pl – Monitor and report on varnish usage
check_varnish.pl [-c|–cache] [-b|–bin
DESCRIPTION
This script will report on various varnish stats including: varnish cache hit ratio backend error count (Total or Ratio) Any other counter in varnishstat If no counters are required the script will ensure the varnish binary is running
OPTIONS
-a –cache – this will make the script output cache_hit ratio perfdata
-b –bin
-d –backend
-h –help – output this message
-w –warning
-c –critical
-s –stats
-t –technique
EXAMPLES
Check varnish is running
./check_varnish.pl
Check varnish Cache Hit Ratio and warn if ratio is below 0.8
./check_varnish.pl -a -w 0.8 -c 0.6
Check varnish Backends
./check_varnish.pl -d all
Check varnish client requests and drops
./check_varnish.pl -s client_drop,client_req
Nagios Set Up
Once you have run the command in the CLI and all is working you can add the command:
define command {
command_name check_varnish
command_line $USER1$/check_varnish.pl $ARG1$
register 1
}
$USER1$ is your variable pointing to your nagios plugins folder and $ARG1$ are any command line arguments you specify in the service.
define service {
host_name localhost
service_description Varnish
check_command check_varnish!–cache -w 0.6 -c 0.4
register 1
}
The service above will give a warning if the hit ratio goes below 0.6 and critical if the ratio goes below 0.4
NRPE
The below is a line that can be used in the NRPE configuration for remote monitoring:
command[check_varnish_cache_hit]=/usr/lib/nagios/plugins/check_varnish.pl –cache -w 0.6 -c 0.4
The NRPE service could look like this:
define service {
host_name varnishserver
service_description Varnish Cache Hit Ratio
check_command check_nrpe!check_varnish_cache_hit
register 1
}
Performance Data
For certain stats the plugin outputs performance data which can be truned into graphs. The graphs below were produced by nagios and nagiosgrapher: This graph show the performance data when varnish was restarted. As you can see the cache suddenly drops off and then slowly builds back up as more users access the site
The graph below shows the cache hit ratio slowly increasing over a week. This means most of the cache has been populated and so most of the request are coming from the cache.
