How to update metrics regularly using prometheus-flask-exporter?

Question

I'm creating a simple Flask webapp which should generate a random metric to be pulled by Prometheus. I'm using the prometheus-flask-exporter library which enabled me to set a metric.

Put simply, I want to know how can I configure custom metrics internally within flask so that they update at intervals from the '/metrics' endpoint of the flask app.

Not 'how often can I get prometheus to fetch a particular metric'

Currently I can't get a loop working within my flask app as the main class doesn't run if I have one.

This is just for a proof of concept, the custom metric can be anything.

My app.py:

from flask import Flask, render_template, request
from prometheus_flask_exporter import PrometheusMetrics

app = Flask(__name__)
metrics = PrometheusMetrics(app)

#Example of exposing information as a Gague metric:
info = metrics.info('random_metric', 'This is a random metric')
info.set(1234)

if __name__ == '__main__':
    app.run(host='0.0.0.0')

Answer 1

I solved this problem by adding a background thread to do the work.

from flask import Flask
import requests
import time
import threading

class HealthChecker():

    def __init__(self):
        self.app = Flask(__name__)

        @self.app.route('/', methods=['GET'])
        def hello_world():
            return "Hello world from Flask"

        self.metrics = PrometheusMetrics(self.app)
        threading.Thread(target = self.pull_metric).start()
   

if __name__ == '__main__':
    healthChecker = HealthChecker()
    self.app.run(host='0.0.0.0')