Deploying to an ELB backed application when you have a deployment script to do on one instance.

deploy_loadbalancer.sh

$LOAD_BALANCER_NAME=""
Instance_ids=`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"`
for $INSTANCE_ID in ${Instance_ids[@]}:
  do
    private_ip=`aws ec2 describe-instances --instance-id $id |jq -r '.Reservations[].Instances[] | .PrivateIpAddress'`
    aws elb deregister-instances-from-load-balancer --load-balancer-name $LOAD_BALANCER_NAME  --instances $INSTANCE_ID
    `ssh $username@$private_ip` < deployment_script.sh
    aws elb register-instances-with-load-balancer --load-balancer-name $LOAD_BALANCER_NAME  --instances $INSTANCE_ID
  done