check_json

Check_json is a Nagios/Icinga2 plugin for monitoring JSON files and URIs with Jq filters.

Requires Python 3.6+

Installation

You can install with pip:

python3 -m pip install check-json

Or install from source:

git clone https://gitlab.com/cspeterson/check_json.git check_json.git
pip install check_json.git

Usage

Pass the plugin any number of Jq filters (with thresholds) and a JSON source. The source can be either a file or an HTTP/S URI.

Essentially, any valid Jq filter you can formulate that returns a numerical value for comparison against its thresholds will work.

The plugin will test the result of each filter against its thresholds and report accordingly.

# usage: check_json [-h] [--filter LABEL FILTER THRESHOLDS] [--verbose] jsonsrc
check_json  --filter 'LABEL1' 'FILTER1' 'wRANGE,cRANGE'  --filter 'LABEL2' 'FILTER2' 'wRANGE,cRANGE'  /path/to/jsonsrc

For example, this will warn if the value of key is more than 10, and will crit if it is more than 20:

check_json --filter 'my_label' '.key' 'w~:10,c~:20'

Or to report numerical {1,0} for perfdata if a string is present:

check_json --filter 'my_label' 'if .key == "some_string" then 1 else 0 end' 'w10,c20'

Check a value only if the timestamp is within the last two minutes:

check_json --filter 'my_label' 'select((.timestamp | tonumber) > (now - 120)) | .key' 'w~:10,c~:20'

For more on Jq filters, refer to the Jq Manual for your version of libjq.

For more on Nagios plugin ranges, thresholds, perfdata, and return codes, see Nagios Plugin Development Guidelines.

Icinga2

Here is an Icinga2 CheckCommand object for this plugin:

object CheckCommand "check_json" {
  command = [ PluginDir + "/check_json", ]
  arguments = {
    # It appears the only way to get Icinga to repeat a particular key *and*
    # pass it multiple separate arguments is to define it multiple times (as
    # below), give them all the same key, and just increment the number for
    # each subsequent usage of the key ¯\_(ツ)_/¯
    "--filter" = {
      description = "Defines a filter, its name, and thresholds."
      key = "--filter"
      repeat_key = false
      value = "$check_json_filter$"
    }
    "--filter0" = {
      description = "Defines a filter, its name, and thresholds."
      key = "--filter"
      repeat_key = false
      value = "$check_json_filter0$"
    }
    "--filter1" = {
      description = "Defines a filter, its name, and thresholds."
      key = "--filter"
      repeat_key = false
      value = "$check_json_filter1$"
    }
    "--filter2" = {
      description = "Defines a filter, its name, and thresholds."
      key = "--filter"
      repeat_key = false
      value = "$check_json_filter2$"
    }
    "--filter3" = {
      description = "Defines a filter, its name, and thresholds."
      key = "--filter"
      repeat_key = false
      value = "$check_json_filter3$"
    }
    "--filter4" = {
      description = "Defines a filter, its name, and thresholds."
      key = "--filter"
      repeat_key = false
      value = "$check_json_filter4$"
    }
    "--filter5" = {
      description = "Defines a filter, its name, and thresholds."
      key = "--filter"
      repeat_key = false
      value = "$check_json_filter5$"
    }
    "--filter6" = {
      description = "Defines a filter, its name, and thresholds."
      key = "--filter"
      repeat_key = false
      value = "$check_json_filter6$"
    }
    jsonsrc = {
      description = "The path to the file to inspect"
      required = true
      skip_key = true
      value = "$check_json_jsonsrc$"
    }
  }
}

And a minimal example Icinga Service:

object Service "host.domain.tld_check" {
  import "generic-service"
  display_name = "Jq JSON filter"
  host_name = "host.domain.tld"
  check_command = "check_json"
  command_endpoint = "host.domain.tld"
  notes = "The `check_json` command is a custom plugin to run Jq filters against JSON files."
  notes_url = "https://gitlab.com/cspeterson/check_json"

  vars.check_json_filter = ["mylabel1". ".somefilter1", "w@0"]
  vars.check_json_filter2 = ["mylabel2". ".somefilter2", "w@0"]
  vars.check_json_jsonfile = "/path/to/file.json"
}

Note: on the command path: the preceeding Icinga2 configuration object points to the check_json command in Icinga2's configured PluginDir, but this can be configured however you like. For instance:

• point it to wherever it is installed by its full path
• symlink from the specified path to the actual script.
• or take the kludge route, leave it as-is, and copy check_json/__main__.py from this repo into PluginDir + "/check_json"

Up to you!

Limitations

What this plugin is not for:

• Exceptionally huge JSON files - this plugin loads the entire JSON file into memory.
• Keeping place in a log file over time. For that (though with admittedly simpler pattern matching), see check_logfiles. For a possible workaround, see the timestamp example under Usage.

Contributing

Pull requests are welcome. For major changes, open an issue first to discuss what you would like to change.

To run the test suite:

# `all` includes venv creation and installation of dependencies
make all

Please make sure to update tests as appropriate.

License

MIT