push_to_gateway function uses PUT method, which is rejected by WSGI server

[mallika-mur]

Hello, I'm still a newbie, so maybe I am misinterpreting something, but it appears as if there's an issue with the push_to_gateway() function defined in exposition.py.

Since v0.21 has been released, I cannot get my custom collector to expose its metrics over HTTP. It appears that even though the WSGI server when start_http_server() only supports OPTION and GET as methods, push_to_gateway() uses PUT, which gives me a "405 Method Not Allowed" error. Since my little program runs flawlessly with v0.20, I'm inclined to believe this may be a bug.

Here's what works in v0.20:

import prometheus_client
from prometheus_client.core import GaugeMetricFamily
import requests
import time


class MyCollector(object):
    def __init__(self):
        pass

    def collect(self):
        datajson = requests.get('https://api.example.com/foo)
        rawdata = datajson.json()

        registry = prometheus_client.CollectorRegistry()
        g = GaugeMetricFamily('mymetric', 'My Gauge Metric', value=rawdata['meta']['total'])
        yield g


if __name__ == '__main__':
    prometheus_client.start_http_server(8000)
    R = prometheus_client.REGISTRY.register(MyCollector())
    while True: 
        prometheus_client.push_to_gateway('localhost:8000', job='gaugemetricvalues', registry=R)
        time.sleep(3600)

[csmarchbanks]

Push to gateway is not meant to push data back to itself, it is meant to push to a separate instance of the Pushgateway. Previously your pushes just were not doing anything, now we have slightly tighter handling of http requests so it is appropriately returning an error indicating that your program is not working as you intend.

[mallika-mur]

So sorry for getting back at this odd time - thank you for that clarification, seems like I misunderstood what the Pushgateway does. However, I do think the docs are a bit confusing about this, I'll try to clarify this in the docs and make a pull request 😄