"Duplicated timeseries in CollectorRegistry" when testing

Hi,

Thanks for this awesome module!

When testing my flask application, I instantiate a new instance of my application for every test using fixtures. For the first test, everything goes right, but on subsequent tests, I get a “Duplicated timeseries” error. My understanding is that PrometheusMetrics uses the same registry for every application. Is this the expected behavior?

Here’s a minimal snippet that reproduces this behaviour.

from flask import Flask
from prometheus_flask_exporter import PrometheusMetrics

app1 = Flask(__name__)
metrics1 = PrometheusMetrics(app1)
# some test

app2 = Flask(__name__)
metrics2 = PrometheusMetrics(app2)
# some other test

The output:

    metrics2 = PrometheusMetrics(app2)
/usr/local/lib/python3.6/site-packages/prometheus_flask_exporter/__init__.py:115: in __init__
    self.init_app(app)
/usr/local/lib/python3.6/site-packages/prometheus_flask_exporter/__init__.py:137: in init_app
    self._defaults_prefix, app
/usr/local/lib/python3.6/site-packages/prometheus_flask_exporter/__init__.py:253: in export_defaults
    **buckets_as_kwargs
/usr/local/lib/python3.6/site-packages/prometheus_client/metrics.py:494: in __init__
    labelvalues=labelvalues,
/usr/local/lib/python3.6/site-packages/prometheus_client/metrics.py:103: in __init__
    registry.register(self)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <prometheus_client.registry.CollectorRegistry object at 0x7f425acb0d68>, collector = <prometheus_client.metrics.Histogram object at 0x7f424a45c3c8>

    def register(self, collector):
        '''Add a collector to the registry.'''
        with self._lock:
            names = self._get_names(collector)
            duplicates = set(self._names_to_collectors).intersection(names)
            if duplicates:
                raise ValueError(
                    'Duplicated timeseries in CollectorRegistry: {0}'.format(
>                       duplicates))
E               ValueError: Duplicated timeseries in CollectorRegistry: {'flask_http_request_duration_seconds_bucket', 'flask_http_request_duration_seconds_count', 'flask_http_request_duration_seconds_sum', 'flask_http_request_duration_seconds_created'}

I was able to get rid of the error by instantiating a new CollectorRegistry at every app instantiation.

from flask import Flask
from prometheus_flask_exporter import PrometheusMetrics
from prometheus_client import CollectorRegistry

app1 = Flask(__name__)
metrics1 = PrometheusMetrics(app1, registry=CollectorRegistry())

app2 = Flask(__name__)
metrics2 = PrometheusMetrics(app2, registry=CollectorRegistry())

Thanks!

[rycus86]

Hi,

Thanks a lot for reporting this!

If this is strictly a testing related problem for you, I’ve solved it exactly the way you described it, by using a new CollectorRegistry for each test: https://github.com/rycus86/prometheus_flask_exporter/blob/master/tests/unittest_helper.py#L22

There’s also a way more hacky approach, where you can unregister all the metrics collectors before each tests, like this: https://github.com/rycus86/webhook-proxy/blob/master/tests/unittest_helper.py#L39

Does this help?

Thanks!

[andersbogsnes]

Sorry for necroing - just remembered that I hadn’t thanked you for putting together the test example!

Great work - much appreciated!