Error with custom labels metrics

Hello, when I update this solution to the 2.0.0 version and try to use custom labels for metric - https://github.com/korfuri/django-prometheus/blob/master/django_prometheus/tests/end2end/testapp/test_middleware_custom_labels.py#L19-L46. I have an exception for each method.

My middleware settings:

MIDDLEWARE = [
    "metrics.middleware_custom_labels.AppMetricsBeforeMiddleware",
    # "django_prometheus.middleware.PrometheusBeforeMiddleware",
    'django.middleware.security.SecurityMiddleware',
    'django.middleware.common.CommonMiddleware',
    # "django_prometheus.middleware.PrometheusAfterMiddleware",
    "metrics.middleware_custom_labels.AppMetricsBeforeMiddleware",
]

My custom middleware:

import logging
from django.conf import settings
# from prometheus_client import REGISTRY
# from prometheus_client.metrics import MetricWrapperBase
from django_prometheus.middleware import (
    Metrics,
    PrometheusAfterMiddleware,
    PrometheusBeforeMiddleware,
)

logger = logging.getLogger(__name__)


class CustomMetrics(Metrics):
    def register_metric(
        self, metric_cls, name, documentation, labelnames=tuple(), **kwargs
    ):
        
        labels = list(labelnames)
        labels.extend(("app", "user_agent_type"))
        labelnames = tuple(labels)
        logger.info(labelnames)

        return super(CustomMetrics, self).register_metric(
            metric_cls, name, documentation, labelnames=labelnames, **kwargs
        )


class AppMetricsBeforeMiddleware(PrometheusBeforeMiddleware):
    metrics_cls = CustomMetrics


class AppMetricsAfterMiddleware(PrometheusAfterMiddleware):
    metrics_cls = CustomMetrics

    def label_metric(self, metric, request, response=None, **labels):
        new_labels = labels
        new_labels = {"app": "my-application-name", "user_agent_type": "api"}
        new_labels.update(labels)
        return super(AppMetricsAfterMiddleware, self).label_metric(
            metric, request, response=response, **new_labels
        )

Versions:

• Django = “2.2.10”
• django-prometheus = “2.0.0”

Exception in log application when I execute some rest method:

[2020-02-24 17:09:30,108 ERROR] django.request | Internal Server Error: /metrics
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/usr/local/lib/python3.7/site-packages/django/utils/deprecation.py", line 93, in __call__
    response = self.process_request(request)
  File "/usr/local/lib/python3.7/site-packages/django_prometheus/middleware.py", line 177, in process_request
    self.metrics.requests_total.inc()
  File "/usr/local/lib/python3.7/site-packages/prometheus_client/metrics.py", line 244, in inc
    self._value.inc(amount)
AttributeError: 'Counter' object has no attribute '_value'
Internal Server Error: /metrics
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/usr/local/lib/python3.7/site-packages/django/utils/deprecation.py", line 93, in __call__
    response = self.process_request(request)
  File "/usr/local/lib/python3.7/site-packages/django_prometheus/middleware.py", line 177, in process_request
    self.metrics.requests_total.inc()
  File "/usr/local/lib/python3.7/site-packages/prometheus_client/metrics.py", line 244, in inc
    self._value.inc(amount)
AttributeError: 'Counter' object has no attribute '_value'
[2020-02-24 17:09:30,108 ERROR] django.request | Internal Server Error: /metrics
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/usr/local/lib/python3.7/site-packages/django/utils/deprecation.py", line 93, in __call__
    response = self.process_request(request)
  File "/usr/local/lib/python3.7/site-packages/django_prometheus/middleware.py", line 177, in process_request
    self.metrics.requests_total.inc()
  File "/usr/local/lib/python3.7/site-packages/prometheus_client/metrics.py", line 244, in inc
    self._value.inc(amount)
AttributeError: 'Counter' object has no attribute '_value'

[hsinghc-plantx]

Thank you @chrinor2002 for the suggestions. I ran into the same issue. Just being verbose about my understanding, the self.metrics.requests_total.inc() call in process_request of the provided Before middleware becomes invalid if we set labelnames to the requests_total metric. Because in that case, requests_total has not been initialized with labelvalues yet.

Although, I went with a little bit different approach. Let’s say we are adding the environment type as a label

class CustomMetrics(Metrics):
    def register_metric(self, metric_cls, name, documentation, labelnames=(), **kwargs):
        ln_list = list(labelnames)
        if len(ln_list) == 0:
            labels = {
                ENV_LABEL: settings.ENV_TYPE
            }
            return super().register_metric(
                metric_cls, name, documentation, labelnames=tuple([ENV_LABEL]), **kwargs
            ).labels(**labels)
        ln_list.append(ENV_LABEL)
        labelnames = tuple(ln_list)
        return super().register_metric(
            metric_cls, name, documentation, labelnames=labelnames, **kwargs
        )


class AppMetricsBeforeMiddleware(PrometheusBeforeMiddleware):
    metrics_cls = CustomMetrics


class AppMetricsAfterMiddleware(PrometheusAfterMiddleware):
    metrics_cls = CustomMetrics

    def label_metric(self, metric, request, response=None, **labels):
        new_labels = {
            ENV_LABEL: settings.ENV_TYPE
        }
        new_labels.update(labels)
        try:
            return super().label_metric(metric, request, response=response, **new_labels)
        except ValueError:
            return super().label_metric(metric, request, response=response)

[samwho]

We’ve also run in to this problem, and would really love a solution that doesn’t involve essentially copy pasting the whole middleware classes with a few tweaks.