Adding the 4 channel relay board ks0212 to the MQTT universe

We just hacked a trotec dehumidifier for Herwigs Observatory. The idea was to additionally activate the dehumidifier when the difference between outside and inside humidity is above 10%. Normally there is a fan taking care of it but sometimes the differents gets to high. As there is already a raspberry pi running in the observatory for the weatherstation and the flightradar24 installation we just added the 4 channel relay board ks0212 from keyestudio. Not touching the 220V part we directly used the relay to “press” the TTL switch on the board for 0.5 seconds to turn on and off the dehumidifier. Here are the code snipped we used for this. The control is completely handled via MQTT.

Installing necessary programs and libraries

sudo apt install python python-pip python-dev
sudo pip install wiringpi paho-mqtt

1 2	sudo apt install python python-pip python-dev sudo pip install wiringpi paho-mqtt

For the sake of simplicity we used python and the GPIO library wiringpi. Therefore we first install the python development parts and them the python libraries for wiringpi and MQTT. As this is a dedicated hardware installation we don’t use virtualenv and directly install the library as root system wide.

The python program

import time
import wiringpi
import paho.mqtt.client as mqtt

def setup():
   wiringpi.wiringPiSetup()
   wiringpi.pinMode(3,  1)
   wiringpi.pinMode(7,  1)
   wiringpi.pinMode(22, 1)
   wiringpi.pinMode(25, 1)

def short(pin):
    switch_on(pin)
    time.sleep(0.5)
    switch_off(pin)

def switch_on(pin):
    wiringpi.digitalWrite(pin, 1)

def switch_off(pin):
    wiringpi.digitalWrite(pin, 0)

def on_connect(self, client, userdata, rc):
    mqclient.subscribe("sternwarte/relay/#")

def on_message(client, userdata, msg):
    m = msg.topic.split("/")
    pin = 0
    if m[-1] == "j3": 
        pin = 3
    if m[-1] == "j2": 
        pin = 7
    if m[-1] == "j4": 
        pin = 22
    if m[-1] == "j5": 
        pin = 25
    if pin != 0:
        if msg.payload == "on":
            switch_on(pin)
        if msg.payload == "off":
            switch_off(pin)
        if msg.payload == "press":
            short(pin)

if __name__ == "__main__":
    setup()
    mqclient = mqtt.Client(clean_session=True)
    mqclient.connect("192.168.2.5", 1883, 60)
    mqclient.on_connect = on_connect
    mqclient.on_message = on_message
    mqclient.loop_forever()

import time

import wiringpi

import paho.mqtt.client as mqtt

def setup():

wiringpi.wiringPiSetup()

wiringpi.pinMode(3, 1)

wiringpi.pinMode(7, 1)

wiringpi.pinMode(22, 1)

wiringpi.pinMode(25, 1)

def short(pin):

switch_on(pin)

time.sleep(0.5)

switch_off(pin)

def switch_on(pin):

wiringpi.digitalWrite(pin, 1)

def switch_off(pin):

wiringpi.digitalWrite(pin, 0)

def on_connect(self, client, userdata, rc):

mqclient.subscribe("sternwarte/relay/#")

def on_message(client, userdata, msg):

m = msg.topic.split("/")

pin = 0

if m[-1] == "j3":

pin = 3

if m[-1] == "j2":

pin = 7

if m[-1] == "j4":

pin = 22

if m[-1] == "j5":

pin = 25

if pin != 0:

if msg.payload == "on":

switch_on(pin)

if msg.payload == "off":

switch_off(pin)

if msg.payload == "press":

short(pin)

if __name__ == "__main__":

setup()

mqclient = mqtt.Client(clean_session=True)

mqclient.connect("192.168.2.5", 1883, 60)

mqclient.on_connect = on_connect

mqclient.on_message = on_message

mqclient.loop_forever()

Again, a very simple python script, basically attaching to a (you need to change the code, there is no config) mqtt server and subscribes itself to a certain topic. Then it waits for messages and cuts off the last part of the topic to identify the relay. The naming convention is based on the relay name printed on the ks0212 pcb. As payload you can send “on“, “off” and “press“. “press” switches the relay on for half a second in order to simulate a button press as we need it for our dehumidifier.

Adding a systemd service

In order to keep the wantabe daemon up and running and also start it automatically at system start we add this service configuration file in “/lib/systemd/system/relayboard.service“:

#cat /lib/systemd/system/relayboard.service
[Unit]
Description=ks0212 Relay Board
After=multi-user.target

[Service]
Type=simple
ExecStart=/usr/bin/python /home/pi/ks0212.py
Restart=on-abort

[Install]
WantedBy=multi-user.target

#cat /lib/systemd/system/relayboard.service

[Unit]

Description=ks0212 Relay Board

After=multi-user.target

[Service]

Type=simple

ExecStart=/usr/bin/python /home/pi/ks0212.py

Restart=on-abort

[Install]

WantedBy=multi-user.target

Activating the service

The following lines activate the service:

sudo chmod 644 /lib/systemd/system/relayboard.service
sudo systemctl daemon-reload
sudo systemctl enable relayboard.service
sudo systemctl start relayboard.service

sudo chmod 644 /lib/systemd/system/relayboard.service

sudo systemctl daemon-reload

sudo systemctl enable relayboard.service

sudo systemctl start relayboard.service

Checking the status can be done with:

sudo systemctl status relayboard.service

1	sudo systemctl status relayboard.service

ks0212 Pinout

If you want to do some hacking with the ks0212 relay board on your own here is the pin mapping table. I used the very cool side https://pinout.xyz/pinout/wiringpi for getting the numbers:

Relay	WiringPi	BCM	GPIO	Link
J2	7	4	7	https://pinout.xyz/pinout/pin7_gpio4
J3	3	22	15	https://pinout.xyz/pinout/pin15_gpio22
J4	22	6	31	https://pinout.xyz/pinout/pin31_gpio6
J5	25	26	37	https://pinout.xyz/pinout/pin37_gpio26

The Idea

Every now and then you want to test your installation, your server or your setup. Specially when you want to test auto scaling functionalities. Kubernetes has an out of the box auto scaler and the official descriptions recommends a test docker container for testing with a apache and php installation. This is really great for testing a web application where you have some workload for a relatively short time frame. But I would also like to test a scenario where the workload runs for a longer time in the kubernetes setup and generates way more cpu workload then a web application. Therefore I hacked a nice docker container based on a c program load generator.

The docker container

The docker container is basically a very very simple Flask server with only one entry point “/”. The workload itself can be configured via two parameters:

percentage How much cpu load will be generated
seconds How long will the workload be active

The docker container itself uses nearly no CPU cycles as Flask is the only python process being active and waits for calls to start using CPU cycles.

lookbusy

I use a very nice open source tool called lookbusy from Devin Carraway which consumes memory and cpu cycles based on command line parameters. Unfortunately the program has no parameter to configure the time span it shout run. Therefore I call it the unix command timeout to terminate its execution after the given amount of seconds.

The Flask python wrapper

import subprocess
from   threading import Thread
from   flask     import Flask, request

app = Flask(__name__)

def worker(percentage, seconds):
    subprocess.run(['timeout', str(seconds), '/usr/local/bin/lookbusy', '-c', str(percentage)])

@app.route('/')
def load(): 
    percentage = request.args.get('percentage') if "percentage" in request.args else 50
    seconds    = request.args.get('seconds')    if "seconds"    in request.args else 10
    Thread(target=worker, args=(percentage, seconds)).start()
    return "started"

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=80, processes=10)

import subprocess

from threading import Thread

from flask import Flask, request

app = Flask(__name__)

def worker(percentage, seconds):

subprocess.run(['timeout', str(seconds), '/usr/local/bin/lookbusy', '-c', str(percentage)])

@app.route('/')

def load():

percentage = request.args.get('percentage') if "percentage" in request.args else 50

seconds = request.args.get('seconds') if "seconds" in request.args else 10

Thread(target=worker, args=(percentage, seconds)).start()

return "started"

if __name__ == "__main__":

app.run(host='0.0.0.0', port=80, processes=10)

The only program is a python Flask one, very short and only takes the get call to its root folder, checks for the two parameters and starts a thread with the subprocess. The get call immediately returns as it also supports long run workload simulations.

The Dockerfile

FROM   python:latest
RUN    curl http://www.devin.com/lookbusy/download/lookbusy-1.4.tar.gz | tar xvz && \
       cd lookbusy-1.4 && ./configure && \
       make && make install && cd .. && rm -rf lookbusy-1.4
RUN    pip install Flask
ADD    server.py server.py
EXPOSE 80
CMD    python -u server.py

FROM python:latest

RUN curl http://www.devin.com/lookbusy/download/lookbusy-1.4.tar.gz | tar xvz && \

cd lookbusy-1.4 && ./configure && \

make && make install && cd .. && rm -rf lookbusy-1.4

RUN pip install Flask

ADD server.py server.py

EXPOSE 80

CMD python -u server.py

The docker container is based on python latest (at this time 3.6.4). I put all the curl, make, install and rm calls into a single line in order to have a minimal footprint for the docker layer as we do not need the source code any more. As Flask is the only requirements I also call it directly without the requirements.txt file. The “-u” parameter for the python call is necessary to prevent python from buffering the output. Otherwise it can be quite disturbing when trying to read the debug log file.

Building and pushing the docker container

docker build -t ansi/lookbusy .
docker push     ansi/lookbusy

1 2	docker build -t ansi/lookbusy . docker push ansi/lookbusy

Building and pushing it to hub.docker.com is straightforward and nothing special.

Testing it on a kubernetes cluster

I have chosen the IBM cloud to test my docker container.

Requesting a kubernetes cluster

Requesting a kubernetes cluster can be done after login with

bx cs cluster-create --name ansi-blogtest --location dal10 --workers 3 --kube-version 1.8.6 --private-vlan 1788637 --public-vlan 1788635 --machine-type b2c.4x16

1	bx cs cluster-create --name ansi-blogtest --location dal10 --workers 3 --kube-version 1.8.6 --private-vlan 1788637 --public-vlan 1788635 --machine-type b2c.4x16

This command uses the bluemix CLI with the cluster plugin to control and configure kubernetes on the IBM infrastructure. The parameters are

–name to give your cluster a name (will be very important later on)
–location which datacenter to use (in this case dallas). Use “bx cs locations” to get your possible locations for the chosen region
–workers how many worker nodes are requested
–kube-version which kubernetes version should be used. Use “bx cs kube-versions” to get the available versions. “(default)” is not part of the parameter call.
–private-vlan which vlan for the private network should be used. Use “bx cs vlans <location>” to get the available public and private vlans
–public-vlan see private vlan
–machine-type which kind of underlying configuration you want to use for your worker node. Use “bx cs machine-types <location>” to get the available machine types. The first number after the “.” is the amount of cores and one after “x” the the amount of RAM in GB.

This command takes some time (~1h) to generate the kubernetes cluster. BTW my bluemix cli docker container has all necessary tools and also a nice script called “start_cluster.sh” to query all parameters and start a new cluster. After the cluster is up and running we can get the kubernetes configuration with

bx cs cluster-config ansi-blog
OK
The configuration for ansi-blogtest was downloaded successfully. Export environment variables to start using Kubernetes.

export KUBECONFIG=/root/.bluemix/plugins/container-service/clusters/ansi-blog/kube-config-dal10-ansi-blog.yml

bx cs cluster-config ansi-blog

The configuration for ansi-blogtest was downloaded successfully. Export environment variables to start using Kubernetes.

export KUBECONFIG=/root/.bluemix/plugins/container-service/clusters/ansi-blog/kube-config-dal10-ansi-blog.yml

Starting a pod and replica set

kubectl run loadtest --image=ansi/lookbusy --requests=cpu=200m

1	kubectl run loadtest --image=ansi/lookbusy --requests=cpu=200m

We start the pod and replica set without a yaml file because the request is very straight forward. Important here is the parameter “–requests“. Without it the autoscaler can not measure the cpu load and it never triggers.

Exposing the http port

kubectl expose deployment loadtest --type=LoadBalancer --name=loadtest --port=80

1	kubectl expose deployment loadtest --type=LoadBalancer --name=loadtest --port=80

Again because the call is so simple we directly call kubectl without a yaml file to expose the Port 80. We can check for the public IP with

kubectl get svc
NAME     TYPE         CLUSTER-IP   EXTERNAL-IP PORT(S)      AGE
loadtest LoadBalancer 172.21.3.160 <pending>   80:31277/TCP 23m

kubectl get svc

NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE

loadtest LoadBalancer 172.21.3.160 <pending> 80:31277/TCP 23m

In case the cloud runs out of public IP addresses and the “EXTERNAL_IP” is still pending after several minutes we can use one of the workers public ip addresses and the dynamic assigned port. The port is visible with “kubectl get svc” at the “PORTS” section. The syntax is as always in docker internalport:externalport. The workers public IP can be checked with

bx cs workers ansi-blog
ID                                               Public IP     Private IP     Machine Type       State  Status Version
kube-dal10-cr1dd768315d654d4bb4340ee8159faa17-w1 169.47.252.96 10.177.184.212 b2c.4x16.encrypted normal Ready  1.8.6_1506

bx cs workers ansi-blog

ID Public IP Private IP Machine Type State Status Version

kube-dal10-cr1dd768315d654d4bb4340ee8159faa17-w1 169.47.252.96 10.177.184.212 b2c.4x16.encrypted normal Ready 1.8.6_1506

So instead of calling our service with a official public ip address on port 80 we can use

http://169.47.252.96:31277

1	http://169.47.252.96:31277

Autoscaler

Kubernetes has a build in horizontal autoscaler which can be started with

kubectl autoscale deployment loadtest --cpu-percent=50 --min=1 --max=10

1	kubectl autoscale deployment loadtest --cpu-percent=50 --min=1 --max=10

In this case it measures the cpu load and starts new pods when the load is over 50%. The autoscaler in this configuration never starts more than 10 and never less than 2 pods. The current measurements and parameters can be checked with

kubectl get hpa
NAME      REFERENCE           TARGETS  MINPODS MAXPODS REPLICAS AGE
loadtest  Deployment/loadtest 0% / 50% 1       10      1        23m

kubectl get hpa

NAME REFERENCE TARGETS MINPODS MAXPODS REPLICAS AGE

loadtest Deployment/loadtest 0% / 50% 1 10 1 23m

So right now the cpu load is 0 and only one replica is running.

Loadtest

Time to get call our container and start the load test. Depending on the URL we an use curl to start the test with

curl "http://169.47.252.96:31277/?seconds=1000&percentage=80"

1	curl "http://169.47.252.96:31277/?seconds=1000&percentage=80"

and check the result after some time with

kubectl get hpa
NAME      REFERENCE           TARGETS  MINPODS MAXPODS REPLICAS AGE
loadtest  Deployment/loadtest 60%/50%  1       10      6        23m