Find the Public Hostname of an Amazon EC2 Instance

If you need to find the public hostname of an Amazon EC2 instance, there is a simple URL which, when cURL'ed will return the hostname:

http://169.254.169.254/latest/meta-data/public-hostname

This URL only works inside the AWS infrastructure (so you must be on an instance to run it properly), but you could easily run:

curl http://169.254.169.254/latest/meta-data/public-hostname

This will return the hostname in the standard format:

ec2-54-123-256-12.compute-1.amazonaws.com

Custom Opsview NRPE Client Agent Service Checks

To install custom checks on Opsview Agents, there are a number of steps that need to be taken. I will assume that the OpsView daemon has already been installed and is running (if not, you can download it here: http://www.opsview.com/technology/downloads/extras/opsview-agents).

First, log into the client on which you want to install a custom check. Then, navigate to the /usr/local/nagios/libexec folder. This is where we will place the actual custom check script you have written. In this case, I will call it "check_test" (it must begin with "check_" to follow the naming conventions. Additionally, the check must return an exit code indicating its status ("0" for "Success", "1" for "Down", etc.).

Now, that you have saved the check_test file in this directory, make it executable and change the owner and group to "nagios".

sudo chmod +x check_test
sudo chown nagios check_test
sudo chgrp nagios check_test

Now, your check is ready to execute, but it must be made available to the NRPE configuration. To do this, navigate to /usr/local/nagios/etc and create a folder called "nrpe_local" if it does not exist already. Then navigate into the folder.

sudo mkdir nrpe_local
cd nrpe_local

Here, create a file called "override.cfg" and change the owner and group to "nagios" just as you did with the script before.

sudo touch override.cfg
sudo chown nagios override.cfg
sudo chgrp nagios override.cfg

Now, open the file in your favorite text editor and add the following line:

command[check_test]=/usr/local/nagios/libexec/check_test

Where "check_test" is the name of your check that you saved earlier.

Save the file, exit, and restart the opsview agent.

sudo service opsview-agent restart

Now, head over to the Opsview web interface on the Opsview server side. Go to Settings > Service Checks and click the + to add a new check. Give it a name "Test Check" and a description of what it does. Then put it into a Service Group or create a new one. It shouldn't need any dependencies, and you can add it to a Host Template as needed. The check type should be "Active Check" and the period, interval, max check attempts, and retry interval can be whatever tou like.

Under "plugin" select "check_nrpe" (not the name of your plugin, which likely won't be in that list).

Under "Arguments" enter the following:

-H $HOSTADDRESS$ -c check_test

Where "check_test is the name of your check. Submit the changes and you should be complete. Reload the configuration and you will see the check show up and it can be added to your host.