AWS -- EC2 ELB -- shell script to change ip in backend varnish incase the ELB ips keeep changing

in AWS the ELP ( load balancer ) ip is dynamic .. so we need to change this in the varnish config file  . this script does the trick .

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#!/bin/bash

#check if varnish is reunning 

#if running reload if not restart 

varnishstatus=$(/usr/bin/pgrep varnishd |wc -l )

if [ $varnishstatus -gt 0  ]

then

vstatus='reload'

else 

vstatus='restart'

fi

#check IP in hosts set in vairrable 

#get array of all ips of cname ---  internal-EC2-ELB-xxxx-xxxxx3xxxx275.ap-southeast-1.elb.amazonaws.com 

temdigcount=/tmp/temdigcount 

tmpbackendconfig=/tmp/tmpbackendconfig

backendconfig='/etc/varnish/health.backend.vcl'

LBS_aws='/etc/varnish/LBS_aws'

touch $LBS_aws

defaultvcl=''

LB2='internal-EC2-ELB-xxxx-xxxxx3xxxx275.ap-southeast-1.elb.amazonaws.com'

OIFS=$IFS 

IFS=$'\n' 

array=($(dig +short $LB2|sort))

IFS=$OIFS

echo ${array[@]} > $temdigcount

DIFF1=`diff $temdigcount $LBS_aws|wc -l `

echo $DIFF1

if [ $DIFF1 -eq 0 ]

then

echo -e "no diff in ip \n"

exit 

fi 

set_count=0

cat /dev/null > $tmpbackendconfig

for i in ${array[@]}

do

let set_count++

 SERVERIP=$i

cat <<EOF >> $tmpbackendconfig

backend health$set_count {

  .host = "$SERVERIP";

  .port = "http";

  .first_byte_timeout = 300s;

  .probe = {

         .request = "GET / HTTP/1.1" "Host: yoursite.com" "Connection: close";

         .interval = 10s;

         .timeout = 10s;

         .window = 5;

         .threshold = 3;

    }

  }

EOF

done

echo -e "\n Bakcend changed, updating VCL and Reloading VARNISH\n\n"

 /bin/cp -f $tmpbackendconfig  $backendconfig

/etc/init.d/varnish reload

 [ -f $FILE ] && \

 cp ${FILE} $FILE_${NOW} && \

 varnishadm -T localhost:1234 vcl.load vcl_${NOW} $FILE && \

 varnishadm -T localhost:1234 vcl.use  vcl_${NOW}  && \

 varnishadm -T localhost:1234 vcl.list |tail -n 3