Detach and Attach a random instance to an ELB.

ELB-detach-attach.sh

#!/bin/bash
LOAD_BALANCER_NAME=$1
Instance_ids_str=`aws elb describe-load-balancers --load-balancer-name $LOAD_BALANCER_NAME --query "LoadBalancerDescriptions[*].{ID:LoadBalancerName,InstanceId:Instances[*].InstanceId}[*]. {ELB:ID,InstanceId:InstanceId[*]}" --output=json |jq -r ".[].InstanceId|@csv" |sed 's/\"//g'`
IFS=',' read -a Instance_ids_array <<< "$Instance_ids_str"
for INSTANCE_ID in ${Instance_ids_array[$RANDOM % ${#Instance_ids_array[@]}]}
do
  aws elb deregister-instances-from-load-balancer --load-balancer-name $LOAD_BALANCER_NAME  --instances $INSTANCE_ID
  aws elb register-instances-with-load-balancer --load-balancer-name $LOAD_BALANCER_NAME  --instances $INSTANCE_ID
done

@acsrujan only one instance needs to be kicked out not all

got it