Nagios Json Plugin

This is a generic plugin for Nagios which checks json values from a given HTTP endpoint against argument specified rules and determines the status and performance data for that service.

Installation

Requirements

• Nagios
• Python

Assuming a standard installation of Nagios, the plugin can be executed from the machine that Nagios is running on.

cp check_http_json.py /usr/local/nagios/libexec/plugins/check_http_json.py
chmod +x /usr/local/nagios/libexec/plugins/check_http_json.py

Add the following service definition to your server config (localhost.cfg):

define service {
        use                             local-service
        host_name                       localhost
        service_description             <command_description>
        check_command                   <command_name>
        }

Add the following command definition to your commands config (commands.config):

define command{
        command_name    <command_name>
        command_line    /usr/bin/python /usr/local/nagios/libexec/plugins/check_http_json.py -H <host>:<port> -p <path> [-e|-q|-l|-g <rules>] [-m <metrics>]
        }

More info about options in Usage.

CLI Usage

Executing ./check_http_json.py -h will yield the following details:

usage: check_http_json.py [-h] -H HOST [-p PATH] [-v DATA]
                          [-e [KEY_LIST [KEY_LIST ...]]]
                          [-q [KEY_VALUE_LIST [KEY_VALUE_LIST ...]]]
                          [-l [KEY_LTE_LIST [KEY_LTE_LIST ...]]]
                          [-g [KEY_GTE_LIST [KEY_GTE_LIST ...]]]
                          [-m [METRIC_LIST [METRIC_LIST ...]]] [-d]

Nagios plugin which checks json values from a given endpoint against argument
specified rules and determines the status and performance data for that
service

optional arguments:
  -h, --help            show this help message and exit
  -H HOST, --host HOST  Host.
  -p PATH, --path PATH  Path.
  -v DATA, --values DATA 
  -e [KEY_LIST [KEY_LIST ...]], --key_exists [KEY_LIST [KEY_LIST ...]]
                        Checks existence of these keys to determine status.
  -q [KEY_VALUE_LIST [KEY_VALUE_LIST ...]], --key_equals [KEY_VALUE_LIST [KEY_VALUE_LIST ...]]
                        Checks equality of these keys and values (key,value
                        key2,value2) to determine status.
  -l [KEY_LTE_LIST [KEY_LTE_LIST ...]], --key_lte [KEY_LTE_LIST [KEY_LTE_LIST ...]]
                        Checks that these keys and values (key,value
                        key2,value2) are less than or equal to the returned
                        json value to determine status.
  -g [KEY_GTE_LIST [KEY_GTE_LIST ...]], --key_gte [KEY_GTE_LIST [KEY_GTE_LIST ...]]
                        Checks that these keys and values (key,value
                        key2,value2) are greater than or equal to the returned
                        json value to determine status.
  -m [METRIC_LIST [METRIC_LIST ...]], --key_metric [METRIC_LIST [METRIC_LIST ...]]
                        Gathers the values of these keys
                        (key,UnitOfMeasure,Min,Max,WarnRange,CriticalRange)
                        for Nagios performance data. More information about
                        Range format and units of measure for nagios can be
                        found at https://nagios-
                        plugins.org/doc/guidelines.html Additional formats for
                        this parameter are: (key), (key,UnitOfMeasure),
                        (key,UnitOfMeasure,Min,Max).
  -d, --debug           Debug mode.

More info about Nagios Range format and Units of Measure can be found at https://nagios-plugins.org/doc/guidelines.html.

Docker Info Example Plugin

Description

Let's say we want to use check_http_json.py to read from Docker's /info HTTP API endpoint with the following parameters:

Connection information

• Host = 127.0.0.1:4243
• Path = /info

Rules for "aliveness"

• Verify that the key Containers exists in the outputted JSON
• Verify that the key IPv4Forwarding has a value of 1
• Verify that the key Debug has a value less than or equal to 2
• Verify that the key Images has a value greater than or equal to 1
• If any of these criteria are not met, report a WARNING to Nagios

Gather Metrics

• Report value of the key Containers with a MinValue of 0 and a MaxValue of 1000 as performance data
• Report value of the key Images as performance data
• Report value of the key NEventsListener as performance data
• Report value of the key NFd as performance data
• Report value of the key NGoroutines as performance data
• Report value of the key SwapLimit as performance data

Service Definition

localhost.cfg

define service {
        use                             local-service
        host_name                       localhost
        service_description             Docker info status checker
        check_command                   check_docker
        }

Command Definition with Arguments

commands.cfg

define command{
        command_name    check_docker
        command_line    /usr/bin/python /usr/local/nagios/libexec/plugins/check_http_json.py -H 127.0.0.1:4243 -p info -e Containers -q IPv4Forwarding,1 -l Debug,2 -g Images,1 -m Containers,,0,1000 Images NEventsListener NFd NGoroutines SwapLimit
        }

Sample Output

OK: Status OK.|'Containers'=1;0;1000 'Images'=11;0;0 'NEventsListener'=3;0;0 'NFd'=10;0;0 'NGoroutines'=14;0;0 'SwapLimit'=1;0;0 

Docker Container Monitor Example Plugin

check_http_json.py is generic enough to read and evaluate rules on any HTTP endpoint that returns JSON. In this example we'll get the status of a specific container using it's ID which camn be found by using the list containers endpoint (curl http://127.0.0.1:4243/containers/json?all=1).

Connection information

• Host = 127.0.0.1:4243
• Path = /containers/2356e8ccb3de8308ccb16cf8f5d157bc85ded5c3d8327b0dfb11818222b6f615/json

Rules for "aliveness"

• Verify that the key ID exists and is equal to the value 2356e8ccb3de8308ccb16cf8f5d157bc85ded5c3d8327b0dfb11818222b6f615
• Verify that the key State.Running has a value of True

Service Definition

localhost.cfg

define service {
        use                             local-service
        host_name                       localhost
        service_description             Docker container liveness check
        check_command                   check_my_container
        }

Command Definition with Arguments

commands.cfg

define command{
        command_name    check_my_container
        command_line    /usr/bin/python /usr/local/nagios/libexec/plugins/check_http_json.py -H 127.0.0.1:4243 -p /containers/2356e8ccb3de8308ccb16cf8f5d157bc85ded5c3d8327b0dfb11818222b6f615/json -q ID,2356e8ccb3de8308ccb16cf8f5d157bc85ded5c3d8327b0dfb11818222b6f615 State.Running,True
        }

Sample Output

WARNING: Status check failed, reason: Value True for key State.Running did not match.

The plugin threw a warning because the Container ID I used on my system has the following State object:

 u'State': {...
            u'Running': False,
            ...

If I change the command to have the parameter -q parameter State.Running,False, the output becomes:

OK: Status OK.