Notify python orion/quantumleap subscription changes

Question

Is there any way to get notified in python when a Quantumleap o Orion subscription fires for a changed value?

Answer 1

I think the simplest way to receive HTTP notifications coming from Orion is to setup an http server to listen those notifications (http requests) within you Python code. For example by using Flask.

Best.

Answer 2

I've dockerized the nickjj web server, switched the bind_host to 0.0.0.0 as specified in the documentation, and exposed the port 8008:8008 in docker-compose.

nickjj Python web server:

from http.server import HTTPServer, BaseHTTPRequestHandler
from sys import argv

BIND_HOST = '0.0.0.0'
PORT = 8008

class SimpleHTTPRequestHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        self.write_response(b'')

    def do_POST(self):
        content_length = int(self.headers.get('content-length', 0))
        body = self.rfile.read(content_length)

        self.write_response(body)

    def write_response(self, content):
        self.send_response(200)
        self.end_headers()
        self.wfile.write(content)

        print(self.headers)
        print(content.decode('utf-8'))


if len(argv) > 1:
    arg = argv[1].split(':')
    BIND_HOST = arg[0]
    PORT = int(arg[1])

print(f'Listening on http://{BIND_HOST}:{PORT}\n')

httpd = HTTPServer((BIND_HOST, PORT), SimpleHTTPRequestHandler)
httpd.serve_forever()

Dockerfile to build the web server service:

# Build the service from the base image
FROM python:3.9.16-alpine3.17

# During building, run the following commands to install dependecies
RUN apk add --no-cache openssl-dev curl-dev
RUN pip install --upgrade pip
# RUN pip install pycurl crate requests

# Set the work directory
WORKDIR /webserver

# Copy in the continer the following files
COPY ./webserver ./webserver

# Run this command at startup
CMD ["python","-u","webserver", "webserver:8008"]

docker-compose configuration for the web server, with curl for debug:

webserver:
  image: webserver
  stdin_open: true # docker run -i
  tty: true        # docker run -t
  container_name: 'webserver'
  ports:
    - "8008:8008"
  networks:
    - default

I've provisioned the relative subscription in Orion:

curl -iX POST \
    'http://localhost:1026/v2/subscriptions/' \
    -H 'Content-Type: application/json' \
    -H 'fiware-service: opcua_car' \
    -H 'fiware-servicepath: /demo' \
    -d '{
  "description": "Subscriptions for Python webserver",
  "subject": {
    "entities": [
      {
        "idPattern": ".*",
        "type": "PLC"
      }
    ],
    "condition": {
      "attrs": [
        "processStatus"
      ]
    }
  },
  "notification": {
    "http": {
      "url": "http://webserver:8008/"
    },
    "attrs": [
      "processStatus"
    ],
    "metadata": [
      "dateCreated",
      "dateModified"
    ]
  },
  "throttling": 1
}'

And I finally get my subscription notifications in Python.