Pythonmetrics.py
Copy
1
import time
2
import random
3
from prometheus_client import (
4
    Counter, Histogram, Gauge, Info,
5
    REGISTRY, make_wsgi_app, generate_latest
6
)
7
from functools import wraps
8
 
9
# ── Define metrics ──────────────────────────────────────────────────
10
 
11
http_requests_total = Counter(
12
    "http_requests_total",
13
    "Total HTTP requests",
14
    ["method", "endpoint", "status"],
15
)
16
 
17
http_request_duration_seconds = Histogram(
18
    "http_request_duration_seconds",
19
    "HTTP request duration in seconds",
20
    ["method", "endpoint"],
21
    # SLO-aligned buckets: 95th% < 200ms, 99th% < 1s
22
    buckets=[0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0],
23
)
24
 
25
active_connections = Gauge(
26
    "active_connections",
27
    "Number of active HTTP connections",
28
)
29
 
30
app_info = Info("app", "Application information")
31
app_info.info({"version": "2.3.1", "env": "production"})
32
 
33
# ── Decorator for automatic instrumentation ─────────────────────────
34
 
35
def track_request(method: str, endpoint: str):
36
    def decorator(func):
37
        @wraps(func)
38
        def wrapper(*args, **kwargs):
39
            active_connections.inc()
40
            start = time.perf_counter()
41
            status = "200"
42
            try:
43
                result = func(*args, **kwargs)
44
                return result
45
            except Exception as e:
46
                status = "500"
47
                raise
48
            finally:
49
                duration = time.perf_counter() - start
50
                http_requests_total.labels(method, endpoint, status).inc()
51
                http_request_duration_seconds.labels(method, endpoint).observe(duration)
52
                active_connections.dec()
53
        return wrapper
54
    return decorator
55
 
56
# ── Example instrumented handlers ──────────────────────────────────
57
 
58
@track_request("GET", "/api/orders")
59
def list_orders():
60
    time.sleep(random.uniform(0.01, 0.2))
61
    return {"orders": []}
62
 
63
@track_request("POST", "/api/orders")
64
def create_order():
65
    time.sleep(random.uniform(0.05, 0.5))
66
    if random.random() < 0.05:  # 5% error rate
67
        raise ValueError("Database connection failed")
68
    return {"order_id": "ORD-001"}
69
 
70
# Simulate traffic
71
for _ in range(100):
72
    try:
73
        list_orders()
74
        create_order()
75
    except Exception:
76
        pass
77
 
78
# Print metrics
79
print(generate_latest(REGISTRY).decode())
80
 
81
# Key PromQL queries:
82
# Error rate: sum(rate(http_requests_total{status=~"5.."}[5m])) / sum(rate(http_requests_total[5m]))
83
# p99 latency: histogram_quantile(0.99, sum(rate(http_request_duration_seconds_bucket[5m])) by (le, endpoint))
84