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VM Monitoring #4 - Monitoring a webserver using Sensu

Monitoring only system resources is not enough, it is possible for our services to fail without any problem with system resources. Example, Nginx could crash, MySQL could stop working etc even when the system is doing fine otherwise.

To be alerted of these, we need to monitor

  1. Whether a process is running (nginx, mysql etc)
  2. Whether the service is responding on their respective ports (80,443 for nginx, 3306 for mysql)

So we will create checks for these

Monitoring running processes

In this case, we have two processes that we want to monitor : Nginx and MySQL

Both are already installed on our wordpress server. If you do not have them, go ahead and install them.

Fetch assets

We will use the nagiosfoundation plugin to monitor running processes

sensuctl asset add ncr-devops-platform/nagiosfoundation -r nagiosfoundation

Update subscription

sensuctl entity list
sensuctl entity update wordpress

For Entity Class, press enter.
For Subscriptions, type system,webserver and press enter.

Create check

sensuctl check create nginx_service \
--command 'check_service --name nginx' \
--interval 15 \
--subscriptions webserver \
--runtime-assets nagiosfoundation

We should see the event in few seconds

sensuctl event list

Go ahead and stop Nginx and see what happens in sensu

Doing an http check

Previously we were checking if the process was running. But this is not enough. It is possible for nginx to be running and still unresponsive. So, we need a check that does an actual http request

Fetch assets

We will use https://bonsai.sensu.io/assets/sensu-plugins/sensu-plugins-http for that

sensuctl asset add sensu-plugins/sensu-plugins-http:6.0.0 -r sensu-plugins-http

We have already added the ruby runtime in the past, if you have not done that, make sure that asset is also added

sensuctl asset add sensu/sensu-ruby-runtime:0.1.0 -r sensu-ruby-runtime

Create check

sensuctl check create nginx_http \
--command 'check-http.rb -u http://localhost' \
--interval 15 \
--subscriptions webserver \
--runtime-assets sensu-plugins-http,sensu-ruby-runtime

Verify

sensuctl event list

Exercises

  1. Create a check to monitor if mysql is running
  2. Create a check to connect to mysql database