Flask-MQTT-Nginx

flask-mqtt-nginx is a multi-container app, with more than one container specified in the same docker-compose.yml file. There are many reasons to specify multiple containers in the same Docker Compose App. One is due to dependencies.

If a container depends on another to start-up, you must use the same docker-compose.yml file to specify and launch both.

The depends_on stanza specifies what service it is dependent on.

flask-mqtt-nginx is a typical python3 Flask app, together with Nginx.

In the containers folder, use git to download flask-mqtt-nginx from the extra-containers repo:

git checkout remotes/fio/tutorials -- flask-mqtt-nginx

The flask-mqtt-nginx application should now be inside your containers folder:

tree -L 2 .

.
├── flask-mqtt-nginx
│   ├── docker-compose.yml
│   └── nginx.conf
├── mosquitto
│   └── docker-compose.yml
├── README.md
├── shellhttpd
│   ├── docker-build.conf
│   ├── docker-compose.yml
│   ├── Dockerfile
│   ├── httpd.sh
│   └── shellhttpd.conf
└── shellhttpd-mqtt
    ├── docker-compose.yml
    ├── Dockerfile
    └── httpd.sh

Check the content flask-mqtt-nginx/docker-compose.yml:

cat flask-mqtt-nginx/docker-compose.yml

version: "3"
services:
  flask-mqtt:
    image: hub.foundries.io/${FACTORY}/flask-mqtt:latest
    restart: unless-stopped
    extra_hosts:
      - "host.docker.internal:host-gateway"
  nginx:
    image: nginx:alpine
    restart: unless-stopped
    volumes:
      - ./nginx.conf:/etc/nginx/conf.d/default.conf
    ports:
      - 80:80
    depends_on:
      - flask-mqtt

The flask-mqtt-nginx/docker-compose.yml file has the configuration for flask-mqtt-nginx:

  • flask-mqtt: Name of the first service.
  • image: Specifies the Docker container image from hub.foundries.io/${FACTORY}/flask-mqtt:latest. This is the container image created by the FoundriesFactory CI based on the Dockerfile in the flask-mqtt folder—which will be downloaded in a moment.
  • extra_hosts: Maps the container to access the device localhost over the address host.docker.internal.
  • nginx: Name of the second service.
  • image: Specifies the Docker container image nginx:alpine from hub.docker.com.
  • depends_on: Make sure that the nginx service starts up after the flask-mqtt service.
  • volume: replaces the Docker container image’s default configuration file /etc/nginx/conf.d/default.conf with nginx.conf from the flask-mqtt-nginx folder.

In the containers folder, use git to download flask-mqtt from the extra-container repo:

git checkout remotes/fio/tutorials -- flask-mqtt

The flask-mqtt application should be inside your containers folder:

tree -L 2 .

.
├── flask-mqtt
│   ├── app.py
│   └── Dockerfile
├── flask-mqtt-nginx
│   ├── docker-compose.yml
│   └── nginx.conf
├── mosquitto
│   └── docker-compose.yml
├── README.md
├── shellhttpd
│   ├── docker-build.conf
│   ├── docker-compose.yml
│   ├── Dockerfile
│   ├── httpd.sh
│   └── shellhttpd.conf
└── shellhttpd-mqtt
    ├── docker-compose.yml
    ├── Dockerfile
    └── httpd.sh

Check the content of your flask-mqtt/Dockerfile file:

cat flask-mqtt/Dockerfile

# flask-mqtt/Dockerfile
FROM alpine

RUN apk add --update py-pip
RUN apk --no-cache add py3-flask
# install python3 dependencies in advance -- we can copy them later
RUN pip install --no-cache --upgrade pip && \
    pip install --no-cache --upgrade Flask-MQTT

ENV FLASK_APP=app.py
ENV PYTHONPATH=/srv
COPY ./app.py /srv/app.py
CMD ["python3", "-m", "flask", "run", "-h", "0.0.0.0"]

The Dockerfile starts by creating a layer from the latest Alpine Docker image.

Next, pip, py3-flask, and Flask-MQTT are installed.

Then, environmental variables for the Flask Application are set. apps.py from your Docker client’s current directory is added to your Docker container Image. The command to execute python3 with flask parameters is configured.

Check the content of flask-mqtt/app.py:

cat flask-mqtt/app.py

# flask-mqtt/app.py
import time
import sys

from flask import Flask
from flask_mqtt import Mqtt

access = 0
app = None
mqtt = None

def create_app():
  print("create_app")
  global app
  app = Flask(__name__)

  app.config['SECRET'] = 'my secret key'
  app.config['TEMPLATES_AUTO_RELOAD'] = True
  app.config['MQTT_BROKER_URL'] = 'host.docker.internal'
  app.config['MQTT_BROKER_PORT'] = 1883
  app.config['MQTT_USERNAME'] = ''
  app.config['MQTT_PASSWORD'] = ''
  app.config['MQTT_KEEPALIVE'] = 5
  app.config['MQTT_TLS_ENABLED'] = False

  global mqtt
  mqtt = init_mqtt(app)

def init_mqtt(app):
  while True:
    try:
      print("init_mqtt: Connecting to MqTT Broker")
      return Mqtt(app)
    except:
      print("init_mqtt:", sys.exc_info()[0])
      time.sleep(10)

create_app()

@app.route('/')
def hello_world():
  global access
  return ('Number of Access on shellhttpd Container ' + str(access))

@mqtt.on_connect()
def handle_connect(client, userdata, flags, rc):
    mqtt.subscribe('containers/requests')

@mqtt.on_message()
def handle_mqtt_message(client, userdata, message):
  if message.payload.decode().startswith('ACCESS='):
    value = message.payload.decode().split('=')
    if value[1].isnumeric():
      global access
      access = int(value[1])

app.py is a typical python3 Flask application. Unlike many “getting started with flask” examples which return Hello World, it will return the Number of Access counter value from shellhttpd.

It also implements MQTT communication and subscribes to the topic containers/requests.

As it receives messages starting with ACCESS=, it parses and gets the value in the access variable.