Demo 1

This demo has two objectives:

• Demonstrate using middleware to calculate metrics
• Demonstrate metric calculation, reporting and analysis

Using middleware to calculate metrics

Depending on your underlying application framework, the mechanism of executing some code before a request is processed and after a request is processed will different. Usually, such code is often executed as middleware. The Flask framework supplies two decorator functions for this purpose:

• before_request allows executing code before a request is processed
• after_request allows executing code after a request is processed (but before a response is returned)

The src sub-directory contains the application code. The main application is defined in app.py with the middleware functions defined in helpers/middleware.py.

Key snippets from app.py

The setup_metrics() function defined in the middleware.py file is called with the app instance we created for our application to register the appropriates function to be called:

from helpers.middleware import setup_metrics
..
app = Flask(__name__)
setup_metrics(app)
..

As far as our metrics reporting is concerned, that's the only change we do to our application.

Key snippets from middleware.py

THe setup_metrics() function which is called by our application above is defined in this module which has the following relevant code:

from flask import request
import time


def start_timer():
    request.start_time = time.time()


def stop_timer(response):
    # convert this into milliseconds for statsd
    resp_time = (time.time() - request.start_time)*1000
    ...
    return response


def setup_metrics(app):
    app.before_request(start_timer)
    app.after_request(stop_timer)

Using the before_request() function, the start_timer() function i

Run demo

• Install docker and docker-compose
• $ sudo docker-compose up

Play with the data

docker-compose run will print a URL which you can copy-paste into the browser on our host.

Then, open the Analysis Jupyter Notebook by navigating to the demo1 directory.