Custom Prometheus Metrics

from prometheus_client import Histogram
from hurricane.metrics import (
    AverageMetric,
    CalculatedMetric,
    CounterMetric,
    ObservedMetric,
    StoredMetric,
)
from hurricane.metrics.registry import registry
from myapp.models import Order


# 1. Counter: Tracks completed checkouts
class CheckoutCounterMetric(CounterMetric):
    code = "ecommerce_checkouts_total"
    description = "Total number of completed checkout operations"


# 2. Stored Metric: Gauge of active connected users
class ActiveSessionsMetric(StoredMetric):
    code = "ecommerce_active_sessions"
    description = "Current number of active authenticated user sessions"


# 3. Calculated Metric: Computes pending orders directly on scrape
class PendingOrdersMetric(CalculatedMetric):
    code = "ecommerce_pending_orders_count"
    description = "Number of orders currently in pending status"

    @classmethod
    def get_value(cls, *args):
        # Executes automatically only when Prometheus scrapes /metrics
        return Order.objects.filter(status="pending").count()


# 4. Average Metric: Running moving average of order values
class AverageOrderValueMetric(AverageMetric):
    code = "ecommerce_order_value_average_dollars"
    description = "Average transaction dollar amount per completed order"


# 5. Observed Metric: Latency histogram for external payment gateway
class PaymentGatewayLatencyMetric(ObservedMetric):
    code = "ecommerce_payment_gateway_latency_seconds"
    description = "Latency distribution of third-party payment provider calls"
    prometheus = Histogram(
        "ecommerce_payment_gateway_latency_seconds",
        "Payment gateway latency in seconds",
        buckets=(0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0),
    )


# Register all custom metrics with Hurricane's registry
registry.register(CheckoutCounterMetric)
registry.register(ActiveSessionsMetric)
registry.register(PendingOrdersMetric)
registry.register(AverageOrderValueMetric)
registry.register(PaymentGatewayLatencyMetric)

import time
from django.http import JsonResponse
from myapp.metrics import (
    AverageOrderValueMetric,
    CheckoutCounterMetric,
    PaymentGatewayLatencyMetric,
)
from myapp.services import charge_payment_provider


def checkout_view(request):
    order_total = float(request.POST.get("total", 0.0))

    # Time external payment provider call
    start_time = time.perf_counter()
    charge_payment_provider(order_total)
    duration = time.perf_counter() - start_time

    # Record metrics
    CheckoutCounterMetric.increment()
    AverageOrderValueMetric.add_value(order_total)
    PaymentGatewayLatencyMetric.observe(duration)

    return JsonResponse({"status": "success"})

from django.contrib.auth.signals import user_logged_in, user_logged_out
from django.dispatch import receiver
from myapp.metrics import ActiveSessionsMetric

# Maintain active session count
_active_users = 0


@receiver(user_logged_in)
def on_user_logged_in(sender, request, user, **kwargs):
    global _active_users
    _active_users += 1
    ActiveSessionsMetric.set(_active_users)


@receiver(user_logged_out)
def on_user_logged_out(sender, request, user, **kwargs):
    global _active_users
    _active_users = max(0, _active_users - 1)
    ActiveSessionsMetric.set(_active_users)