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Check JSON responses with Nagios

By Brian Buchalter
March 18, 2012

As the developer’s love affair with JSON continues to grow, the need to monitor successful JSON output does as well. I wanted a Nagios plugin which would do a few things:

  • Confirm the content-type of the response header was “application/json”
  • Decode the response to verify it is parsable JSON
  • Optionally, verify the JSON response against a data file

Verify content of JSON response

For the most part, Perl’s LWP::UserAgent class makes short work of the first requirement. Using $response->header("content-type") the plugin is able to check the content-type easily. Next up, we use the JSON module’s decode function to see if we can successfully decode $response->content.

Optionally, we can give the plugin an absolute path to a file which contains a Perl hash which can be iterated through in attempt to find corresponding key/value pairs in the decoded JSON response. For each key/value in the hash it doesn’t find in the JSON response, it will append the expected and actual results to the output string, exiting with a critical status. Currently there’s no way to check a key/value does not appear in the response, but feel free to make a pull request on check_json on my GitHub page.

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