#!/bin/bash

MAX_INSTANCES=9

MIN_INSTANCES=3

SCALE_STEP=2

CPU_BUSY_THRESHOLD=300

CPU_IDLE_THRESHOLD=220

app_status=$(cf app catalog-web)

scale_direction=""

# This function will check the average CPU usage of all running instances of an app

function set_scale_direction {

# Extract lines containing 'running'

running_lines=$(echo "$app_status" | grep "#[0-9]*[[:space:]]*running")

cpu_sum=0

count=0

if [ -n "$running_lines" ]; then

while IFS= read -r line

do

# Extract CPU usage and remove '%' character

cpu_usage=$(echo $line | cut -d' ' -f4 | tr -d '%')

cpu_sum=$(echo "$cpu_sum + $cpu_usage" | bc)

((count++))

done <<< "$running_lines"

fi

# Calculate average CPU usage

average_cpu=$(echo "scale=2; $cpu_sum / $count" | bc)

if [ "$(echo "$average_cpu > $CPU_BUSY_THRESHOLD" | bc)" -eq 1 ]; then

echo "Average CPU is $average_cpu. Too High."

scale_direction="up"

elif [ "$(echo "$average_cpu < $CPU_IDLE_THRESHOLD" | bc)" -eq 1 ]; then

echo "Average CPU is $average_cpu. Too Low."

scale_direction="down"

else

echo "Average CPU is $average_cpu. Just Right."

scale_direction="same"

fi

}

function set_scale_number {

# get the total number of instances

total_instances=$(echo "$app_status" | grep '^instances:' | awk '{print $2}' | cut -d '/' -f 2 | head -n 1)

# exit if the total instances is not a number

if ! [[ "$total_instances" =~ ^[0-9]+$ ]]; then

echo "Total instances is not a number. Exiting. Here is the output of the app status:"

echo "$app_status"

exit 1

fi

echo "Current total instances: $total_instances"

# call the scale direction

set_scale_direction

# if the direction is up and the total instances is less than the max instances

if [ "$scale_direction" == "up" ] && [ "$total_instances" -lt "$MAX_INSTANCES" ]; then

export scale_to=$((total_instances + SCALE_STEP))

echo "Scaling up to $scale_to"

elif [ "$scale_direction" == "down" ] && [ "$total_instances" -gt "$MIN_INSTANCES" ]; then

# export the scale_to value but make sure scale_to is large than 1

export scale_to=$((total_instances - SCALE_STEP < 1 ? 1 : total_instances - SCALE_STEP))

echo "Scaling down to $scale_to"

else

export scale_to="$total_instances"

echo "Remain at the $scale_direction scale level $scale_to"

fi

}