Warning: Silently ignoring app.run() because the application is run from the flask command line executable

An awkward situation. Code:

metrics = prometheus_flask_exporter.PrometheusMetrics(app)
metrics.start_http_server(8081, host=config.METRICS_HOST)

Result:

website_1   |  * Serving Flask app 'src.app:app' (lazy loading)
website_1   |  * Environment: development
website_1   |  * Debug mode: on
website_1   | /usr/local/lib/python3.8/dist-packages/prometheus_flask_exporter/__init__.py:322: Warning: Silently ignoring app.run() because the application is run from the flask command line executable. Consider putting app.run() behind an if __name__ == "__main__" guard to silence this warning.

And the metrics server does not listen on port 8081. It seems that Flask notices that I have invoked the main application using flask run, and has elected to disable the ability to run new Flask applications, which obviously breaks start_http_server from prometheus_flask_exporter.

Not sure what the best way to handle this is, but wanted to flag.

[reubano]

My suggestion was an alternative to os.environ.pop("FLASK_ENV"). You should still use a Production server in production. But the Flask dev server is fine in development.

In my case, I’m doing the following

os.environ.pop("FLASK_RUN_FROM_CLI")
app.run(debug=False, use_reloader=False)

[rycus86]

They already have different (more robust?) ways to expose metrics over HTTP, see https://github.com/prometheus/client_python#http

so it is not secure and should not be used in production

Maybe this is worth calling out in this project’s README, and suggest some alternatives - though on that note I think if you run the metrics endpoint on an insecure server that is not available for external users, it may be something that is an acceptable tradeoff for some. I liked @raxod502 's suggestion to package up the metrics exposure code as a function so that people can bring their own (more secure) servers to serve it with, and perhaps here we can explain in the README that it’s more recommended than the other alternative.