check_http_json.rb

This is a plugin for Nagios that will parse JSON from an HTTP response. It is written in Ruby and is known to function in versions 1.8.7, 1.9.3, and 2.4.0.

Usage

Usage: ./check_http_json.rb -u <URI> -e <element> -w <warn> -c <crit>
    -h, --help                       Help info.
    -v, --verbose                    Additional human output.
    -u, --uri URI                    Target URI. Incompatible with -f.
        --user USERNAME              HTTP basic authentication username.
        --pass PASSWORD              HTTP basic authentication password.
        --headers HEADERS            Comma-separated list of HTTP headers to include (ex. HOST:somehost,AUTH:letmein).
        --status_level STRING        Comma-separated list of HTTP status codes and their associated Nagios alert levels (ex. 301:1,404:2).
        --status_level_default VALUE The default return code for unexpected HTTP status codes. Defaults to 1.
    -f, --file PATH                  Target file. Incompatible with -u.
    -e, --element ELEMENT...         Desired element (ex. foo=>bar=>ish is foo.bar.ish). Repeatable argument.
    -E, --element_regex REGEX        Desired element expressed as regular expression.
        --element_regex_global       Check all occurring matches. -E is required.
    -d, --delimiter CHARACTER        Element delimiter (default is period).
    -w, --warn VALUE                 Warning threshold (integer or Nagios threshold ranges format).
    -c, --crit VALUE                 Critical threshold (integer or Nagios threshold ranges format).
    -r, --result STRING              Expected string result. No need for -w or -c.
    -R, --result_regex REGEX         Expected string result expressed as regular expression. No need for -w or -c.
    -W, --result_warn STRING         Warning if element is [string]. -C is required.
    -U, --result_unknown STRING      Unknown if element is [string]. -C is required.
    -C, --result_crit STRING         Critical if element is [string]. -W is required.
        --result_warn_regex REGEX    Warning if element matches REGEX. --result_crit_regex is required.
        --result_unknown_regex REGEX Unknown if element matches REGEX. --result_crit_regex is required.
        --result_crit_regex REGEX    Critical if element matches REGEX. --result_warn_regex is required.
    -p, --perf ELEMENT               Output additional fields (performance metrics).
        --perf_splitter CHARACTER    Additional fields delimiter (default is comma).
        --output_alt_pipe CHARACTER  Specify a character to replace reserved pipes in the output. Default: !
        --perf_regex REGEX           Output additional fields expressed as regular expression.
        --perf_regex_global          Check all occurring matches. --perf-regex is required.
    -t, --timeout SECONDS            Wait before HTTP timeout.

The --warn and --crit arguments conform to the Nagios threshold format guidelines.

If a simple result of either string or regular expression (-r or -R) is specified:

• A match is OK and anything else is CRIT.
• The warn / crit thresholds will be ignored.

If the warn and crit results (-W and -C) or regular expressions (--result_warn_regex and --result_crit_regex) are specified:

• A match is WARN or CRIT and anything else is OK.
• The warn / crit thresholds will be ignored.

Note that (-r or -R), (-W and -C), and (--result_warn_regex and --result_crit_regex) are mutually exclusive.

Note also that the response must be pure JSON. Bad things happen if this isn't the case.

Implementation

How you choose to implement the plugin is up to you. Here are some suggestions:

given string element, check string result

define command {
    command_name    check_http_json-string
    command_line    /etc/nagios3/plugins/check_http_json.rb -u 'http://$HOSTNAME$:$ARG1$/$ARG2$' -e '$ARG3$' -r '$ARG4$'
}
define service {
    service_description     elasticsearch-cluster-status
    check_command           check_http_json-string!9200!_cluster/health!status!green
}

wildly generic

define command {
    command_name    check_http_json
    command_line    /etc/nagios3/plugins/check_http_json.rb -u 'http://$HOSTNAME$:$ARG1$/$ARG2$' $ARG3$
}
define service {
    service_description     elasticsearch-resident-memory
    check_command           check_http_json!9280!_cluster/nodes/_local/stats!-E resident_in_bytes -w 1024000000 -c 1536000000
}

How are you implementing it?

I encourage you to add your implementation to the wiki - that way everybody can benefit!

Fin

The script is licensed using the Apache License, Version 2.0.

Finally, I invite you to peruse the list of contributors; thank you, all!

GitHub pull requests welcome.