Counters: Tracking Metrics that Only Go Up

In the following example, we start by instantiating the Flask application and defining the Prometheus counters:

home_page_visits: to track the number of visits to the home page (/ endpoint).
about_page_visits: to track the number of visits to the about page (/about endpoint).

Using the following HELP descriptions:

Number of visits to the home page
Number of visits to the about page

The TYPE of both metrics is counter, since they are monotonically increasing metrics.

This is the code:

# Create a Flask application
app = Flask(__name__)

# Define Prometheus counters
home_counter = Counter(
    'home_page_visits',
    'Number of visits to the home page'
)

about_counter = Counter(
    'about_page_visits',
    'Number of visits to the about page'
)

When scraping the /metrics endpoint, Prometheus will see the following output for the two counters:

# HELP home_page_visits_total Number of visits to the home page
# TYPE home_page_visits_total counter
home_page_visits_total 0.0 # Or higher value if incremented

# HELP about_page_visits_total Number of visits to the about page
# TYPE about_page_visits_total counter
about_page_visits_total 0.0 # Or higher value if incremented

Next, we create two routes for the home and about pages:

@app.route('/')
def home():
    """ Route for the home page """
    # Increment the counter for the home page visits
    home_counter.inc()
    return "Welcome to the Home Page
"


@app.route('/about')
def about():
    """ Route for the about page """
    # Increment the counter for the about page visits
    about_counter.inc()
    return "Welcome to the About Page
"

Notice that we increment the counters home_counter and about_counter every time a request is made to the home and about pages, respectively.

Finally, we expose the Prometheus metrics endpoint:

@app.route('/metrics')
def metrics():
    """ Expose the Prometheus metrics """
    return Response(
        generate_latest(),
        mimetype=CONTENT_TYPE_LATEST
    )

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=3000)

Use the following command to create the full app (on server1):

cat <<EOF > /prometheus-python-example/using_counters

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