Sometimes you want to double the number of instances they to receive the new version, and then Autoscaling to hande the magic

Predeploy_Instance_Count_Adjust.sh

#!/usr/bin/env bash
#
# Double the instance count for widget ASG 
# Required ENV Variables
# * ELB_NAME
# * ASG_NAME
#

asg_check() {
  local pending_instance_count=$(aws autoscaling describe-auto-scaling-groups \
    --query 'length(AutoScalingGroups[].Instances[?LifecycleState==`Pending`].InstanceId[])' \
    --auto-scaling-group-names ${ASG_NAME})
  if [[ $pending_instance_count -ne "0" ]]; then
    return 3
  else 
    return 0
  fi
}

elb_check() {
  local outofservice_instance_count=$(aws elb describe-instance-health \
    --load-balancer-name ${ELB_NAME} \
    --query 'length(InstanceStates[?State==`OutOfService`].InstanceId)')
  if [[ $outofservice_instance_count -ne "0" ]]; then
    return 3
  else 
    return 0
  fi
}

wait_for() {
  local check_function=$1
  while ! $(eval $check_function) ; do
    sleep 15
    echo "."
  done
}

check_for_instances_in_service() {
  INSTANCES_IN_SERVICE=$(aws elb describe-instance-health \
  --load-balancer-name ${ELB_NAME} \
  --query 'length(InstanceStates[?State==`InService`].InstanceId)')
}

echo "Checking number of InService instances for ElasticLoadBalancer™"
check_for_instances_in_service

echo "Ok, We got ${INSTANCES_IN_SERVICE} InService instances running"

DESIRED_INSTANCES=$(expr $INSTANCES_IN_SERVICE \* 2)

echo "Let's make it ${DESIRED_INSTANCES}"
aws autoscaling set-desired-capacity --auto-scaling-group-name ${ASG_NAME} --desired-capacity ${DESIRED_INSTANCES} --no-honor-cooldown

echo "Wait for Autoscale to Pend the machines"
sleep 30

echo "Waiting for Autoscale to add Instances"
wait_for asg_check

echo "Waiting for Instances to be InService in ElasticLoadBalancer™"
wait_for elb_check

check_for_instances_in_service
echo "Well, I'm done"
echo "Now we got ${INSTANCES_IN_SERVICE} InService instances running"