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 [-B AUTH] [-p PATH]
                          [-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 ...]]] [-s]
                          [-f SEPARATOR] [-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.
  -B AUTH, --basic-auth AUTH
                        Basic auth string "username:password"
  -p PATH, --path PATH  Path.
  -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).
  -s, --ssl             HTTPS mode.
  -f SEPARATOR, --field_separator SEPARATOR
                        Json Field separator, defaults to "." ; Select element
                        in an array with "(" ")"
  -d, --debug           Debug mode.

Access a specific JSON field by following this syntax: alpha.beta.gamma(3).theta.omega(0) Dots are field separators (changeable), parantheses are for entering arrays.

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.

Dropwizard / Fieldnames Containing '.' Example

Simply choose a separator to deal with data such as this:

{ "gauges": { "jvm.buffers.direct.capacity": {"value": 215415}}}

In this example I've chosen _ to separate guages from jvm and capacity from value. The CLI invocation then becomes:

./check_http_json.py -H localhost:8081 -p metrics --key_exists gauges_jvm.buffers.direct.capacity_value -f _

License

Copyright 2014-2015 Drew Kerrigan.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.