Recently I created a new nagios plugin which check the no. of instances attached in ELB (Elastic Load Balancer) . Here we are talking about ELB in AWS (Amazon Web Service) Cloud. Elastic Load Balancing automatically distributes incoming application traffic across multiple Amazon EC2 instances in the cloud.

Details of check_ELBinstance nagios plugin

Requirement : To check no. of desired instances attached in ELB. If no. of instances count does’nt match then send the alert (Critical)
By this way we can monitor, if desired number of instances in ELB increased or decreased in number.

Scripting : Bash scripting is used for creating the check_ELBinstance nagios plugin.

Prerequisite

Install aws command line interface on Nagios Server. It requires Python 2.6.5 or higher.
Run the below given command –

pip install awscli

Download check_ELBinstance

You can download this plugin and do changes as per your requirement.
I have saved this nagios plugin in github. The given below is the link

https://github.com/sharadchhetri/Nagios/blob/master/check_ELBinstance.sh

In either way you can create a file check_ELBinstance.sh in nagios plugin directory on Nagios Server. And copy paste the below given contents.

#!/bin/bash
#
# Author : Sharad Kumar Chhetri
# Date Of Creation : 1-Nov-2014
# Version  : 1.0
# Description : It checks the no. of instances available in ELB . When the instances count do not matches as per desire value it will send alert.
# Blog : https://sharadchhetri.com
# 

### Supportive URL : http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSGettingStartedGuide/AWSCredentials.html ###

export AWS_ACCESS_KEY_ID="XXXXXXXXXXXXXXXXXXX"
export AWS_SECRET_ACCESS_KEY="YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY"

#### For getting Region infromation,Reference URL: http://docs.aws.amazon.com/general/latest/gr/rande.html

REGION=us-west-1

## In ELB_NAME - Provide name of ELB

ELB_NAME=ProductionELB

## In INSTANCE_COUNT give the value of desired number of Instances should be in ELB

INSTANCE_COUNT=4

## The ELB_INSTANCE_COUNT gives output of no. of  instances attached in ELB
ELB_INSTANCE_COUNT=$(aws --region $REGION elb describe-load-balancers --load-balancer-names $ELB_NAME --output text|grep INSTANCES|wc -l)


if [ "$ELB_INSTANCE_COUNT" == "$INSTANCE_COUNT" ]
then
echo "OK: Total no. of instances $ELB_INSTANCE_COUNT found in ELB $ELB_NAME"
exit 0
else
if [ "$ELB_INSTANCE_COUNT" != "$INSTANCE_COUNT" ]
then
echo "CRIT: Number of instances in ELB $ELB_NAME do not matches with desired value"
exit 2
fi
fi