Python AWS EMR Status via Arduino Uno LEDs

In this post, I’ll share some code I use to check if I left an AWS EMR cluster running by lighting a red (off) or green (on) LED hooked up to an Arduino Uno. This sounds silly but it helps me remember to terminate my clusters before I leave work. Besides, what else am I going to do with a spare Arduino? :)

For this project I used an Arduino Uno, breadboard, 2x 220Ω resistors (red, red, brown, gold), a red LED, a green LED, and wire attached to ground, and 2 wires connected to digital pins (12 and 13).

Arduino with LEDs

I added the following code and flashed it to the Arduino Uno. It initializes the LED pins, reads from the serial connection, and sets the LEDs to on/off based on the bytes received from the USB connection.

// define pins for leds
int ledPinGreen = 12;
int ledPinRed = 13;

int incomingByte = 0;

void setup() {
  // put your setup code here, to run once:

  // set pin modes to output for leds
  pinMode(ledPinGreen, OUTPUT);
  pinMode(ledPinRed, OUTPUT);

  // init serial connection

void loop() {
  // put your main code here, to run repeatedly:

  if (Serial.available() > 0) {
    // read the incoming byte
    incomingByte =;

    if (incomingByte == '1') {
      // 1|true: set green led to on, red to off
      digitalWrite(ledPinGreen, HIGH);
      digitalWrite(ledPinRed, LOW);
    } else {
      // 0|false: set green led to off, red to on
      digitalWrite(ledPinGreen, LOW);
      digitalWrite(ledPinRed, HIGH);



I then added a Python script that uses boto3 (AWS SDK for Python) to check if a cluster is running that matches my name or tags. It then writes 1 or 0 to the (USB) serial connection based on the response and loops with a delay.

import boto3
from time import sleep
import serial

# string to match on cluster name and cluster tags
matching_name = 'Eric'

# USB/serial connection
serial_device = '/dev/tty.usbmodem1411'
serial_speed = 9600

class EmrWatcher:
    def __init__(self, matching_name, serial_device, serial_speed):
        self.matching_name = matching_name.lower()
        self.client = boto3.client('emr')

        self.serial_client = serial.Serial(serial_device, serial_speed)

    # main loop. send 0|1 bytes to arduino based on boolean response from check clusters method
    def watch(self):
        while True:
            result = self.__check_clusters()
            print result

            if result == True:
                byteString = '1'
                byteString = '0'


    # check cluster name and cluster tags for match. return boolean
    def __check_clusters(self):
        clusters = self.__emr_clusters()
        for cluster in clusters['Clusters']:
            cluster_name_matches = self.__cluster_name_matches(cluster)
            if cluster_name_matches:
                return True
            cluster_tags_match = self.__cluster_tags_match(cluster)
            if cluster_tags_match:
                return True
        return False

    # check cluster name for match. return boolean
    def __cluster_name_matches(self, cluster):
        if self.matching_name in cluster['Name'].lower():
            return True
            return False

    # check cluster tags for match. return boolean
    def __cluster_tags_match(self, cluster):
        cluster_description = self.__emr_cluster_description(cluster)
        cluster_tags = self.__emr_cluster_tags(cluster_description)
        tags_string = self.__cluster_tags_string(cluster_tags)
        if self.matching_name in tags_string.lower():
            return True
            return False

    # create single tags string for comparison
    def __cluster_tags_string(self, cluster_tags):
        tag_values = [d['Value'] for d in cluster_tags]
        return "".join(tag_values)

    # fetch cluster description, for tags
    def __emr_cluster_description(self, cluster):
        return self.client.describe_cluster(

    # fetch cluster tags from description
    def __emr_cluster_tags(self, cluster_description):
        return cluster_description['Cluster']['Tags'];

    # fetch a list of non-terminated clusters
    def __emr_clusters(self):
        return self.client.list_clusters(

emr_watcher = EmrWatcher(matching_name, serial_device, serial_speed)

I turned on the Arduino Uno and executed python from my Mac to start the process. If I have an EMR cluster running, it lights the green LED. Else, the red LED is lit. Super helpful.

Source code on Github