Using Python client for Prometheus on IPv6

Question

I am writing a custom exporter for my application using the official Python client for Prometheus My code works fine with the below snippet, (I'm redacting the rest of the code as I think it is irrelevant to the issue I'm facing.)

from prometheus_client import start_http_server, Gauge
start_http_server(9669)

I'm able to get the response if I do

curl --noproxy "*" -v http://localhost:9669/metrics

from the same machine. The issue here is my servers on IPv6. So this endpoint is not reachable from the server where I have Prometheus running. How can make

start_http_server

on IPv6 or is there a workaround for this?

I tried running a flask app and doing curl from the machine where I have Prometheus installed. I do not get response for

from flask import Flask

app = Flask(__name__)

@app.route('/hello')
def hello_world():
    return 'Hello, World!'

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=8989)

but I get response if I modify the line to

app.run(host='::', port=8989)

So I figured I need to run the Prometheus

start_http_server

on IPv6. I tried

start_http_server(9669, addr='[::]')

but I get the error

socket.gaierror: [Errno -2] Name or service not known

and for

start_http_server(9669, addr='::')

I get the error

socket.gaierror: [Errno -9] Address family for hostname not supported

Florian Bach · Accepted Answer · 2024-01-18 16:16:12Z

3

You might be using an old version of the Python Prometheus client.

I tried the most recent version 0.19.0 with Python 3.8, and this code is working just fine for me (server listens on IPv6):

from prometheus_client import start_http_server

if __name__ == '__main__':
    start_http_server(9999, addr='::')
    while True:
        pass

According to a Google search, your bug ("Address family for hostname not supported") was reported here, fixed in this PR, and then released in 0.14.0 from April 2022.

answered Jan 18, 2024 at 16:16

Florian Bach

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