┌─────────────────────────────────────────────────────────────────┐
│                    OBSERVABILITY                                │
├────────────────┬───────────────┬──────────────┬────────────────┤
│    METRICS     │   LOGGING     │   TRACING    │   ALERTING     │
│                │               │              │                │
│  Prometheus    │  structlog    │ OpenTelemetry│  Alert rules   │
│  counters,     │  structured   │ distributed  │  thresholds,   │
│  histograms,   │  JSON logs,   │ trace spans, │  notification  │
│  gauges        │  context      │ correlation  │  channels      │
├────────────────┴───────────────┴──────────────┴────────────────┤
│                    DASHBOARDS (Grafana)                         │
│        Visualize metrics, logs, and traces in one place        │
└─────────────────────────────────────────────────────────────────┘

from prometheus_client import Counter, Histogram, Gauge, Info

**FastAPI middleware for automatic metrics:**

```python
import time
from starlette.middleware.base import BaseHTTPMiddleware
from starlette.requests import Request

class PrometheusMiddleware(BaseHTTPMiddleware):
    async def dispatch(self, request: Request, call_next):
        method = request.method
        endpoint = request.url.path
        start_time = time.perf_counter()

        response = await call_next(request)

        duration = time.perf_counter() - start_time
        status_code = str(response.status_code)

        REQUEST_COUNT.labels(
            method=method, endpoint=endpoint, status_code=status_code
        ).inc()

        REQUEST_DURATION.labels(
            method=method, endpoint=endpoint
        ).observe(duration)

        return response

import structlog

structlog.configure(
    processors=[
        structlog.contextvars.merge_contextvars,
        structlog.stdlib.filter_by_level,
        structlog.stdlib.add_logger_name,
        structlog.stdlib.add_log_level,
        structlog.stdlib.PositionalArgumentsFormatter(),
        structlog.processors.TimeStamper(fmt="iso"),
        structlog.processors.StackInfoRenderer(),
        structlog.processors.format_exc_info,
        structlog.processors.UnicodeDecoder(),
        structlog.processors.JSONRenderer(),
    ],
    wrapper_class=structlog.stdlib.BoundLogger,
    context_class=dict,
    logger_factory=structlog.stdlib.LoggerFactory(),
    cache_logger_on_first_use=True,
)

from starlette.middleware.base import BaseHTTPMiddleware
import structlog
import uuid

class LoggingContextMiddleware(BaseHTTPMiddleware):
    async def dispatch(self, request, call_next):
        request_id = request.headers.get("X-Request-ID", str(uuid.uuid4()))
        structlog.contextvars.clear_contextvars()
        structlog.contextvars.bind_contextvars(
            request_id=request_id,
            method=request.method,
            path=request.url.path,
        )
        response = await call_next(request)
        response.headers["X-Request-ID"] = request_id
        return response

from opentelemetry import trace
from opentelemetry.exporter.otlp.proto.grpc.trace_exporter import OTLPSpanExporter
from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor
from opentelemetry.instrumentation.sqlalchemy import SQLAlchemyInstrumentor
from opentelemetry.instrumentation.redis import RedisInstrumentor
from opentelemetry.sdk.resources import Resource
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import BatchSpanProcessor

def setup_tracing(app, service_name: str = "backend"):
    resource = Resource.create({"service.name": service_name})
    provider = TracerProvider(resource=resource)

    exporter = OTLPSpanExporter(endpoint="http://otel-collector:4317")
    provider.add_span_processor(BatchSpanProcessor(exporter))

    trace.set_tracer_provider(provider)

    # Auto-instrument FastAPI, SQLAlchemy, Redis
    FastAPIInstrumentor.instrument_app(app)
    SQLAlchemyInstrumentor().instrument()
    RedisInstrumentor().instrument()

tracer = trace.get_tracer(__name__)

async def process_order(order_id: str):
    with tracer.start_as_current_span("process_order") as span:
        span.set_attribute("order.id", order_id)

        with tracer.start_as_current_span("validate_order"):
            await validate_order(order_id)

        with tracer.start_as_current_span("charge_payment"):
            result = await charge_payment(order_id)
            span.set_attribute("payment.status", result.status)

        with tracer.start_as_current_span("send_confirmation"):
            await send_confirmation(order_id)

from fastapi import APIRouter, Depends
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy import text
from datetime import datetime, timezone

router = APIRouter(tags=["health"])

@router.get("/health")
async def liveness():
    """Liveness probe -- is the process running?"""
    return {
        "status": "healthy",
        "timestamp": datetime.now(timezone.utc).isoformat(),
        "version": settings.APP_VERSION,
    }

@router.get("/health/ready")
async def readiness(db: AsyncSession = Depends(get_db)):
    """Readiness probe -- can we handle traffic?"""
    checks = {}

    # Check database
    try:
        await db.execute(text("SELECT 1"))
        checks["database"] = {"status": "ok", "latency_ms": 0}
    except Exception as e:
        checks["database"] = {"status": "error", "error": str(e)}

    # Check Redis
    try:
        start = time.perf_counter()
        await redis.ping()
        latency = (time.perf_counter() - start) * 1000
        checks["redis"] = {"status": "ok", "latency_ms": round(latency, 2)}
    except Exception as e:
        checks["redis"] = {"status": "error", "error": str(e)}

    all_ok = all(c["status"] == "ok" for c in checks.values())
    return JSONResponse(
        status_code=200 if all_ok else 503,
        content={
            "status": "ready" if all_ok else "not_ready",
            "checks": checks,
            "timestamp": datetime.now(timezone.utc).isoformat(),
        },
    )

import sentry_sdk
from sentry_sdk.integrations.fastapi import FastApiIntegration
from sentry_sdk.integrations.sqlalchemy import SqlalchemyIntegration

sentry_sdk.init(
    dsn=settings.SENTRY_DSN,
    environment=settings.APP_ENV,
    release=settings.APP_VERSION,
    traces_sample_rate=0.1,  # 10% of requests for performance monitoring
    profiles_sample_rate=0.1,
    integrations=[
        FastApiIntegration(),
        SqlalchemyIntegration(),
    ],
    # Do not send PII
    send_default_pii=False,
    # Filter out health check noise
    before_send=filter_health_checks,
)

def filter_health_checks(event, hint):
    """Do not send health check errors to Sentry."""
    if "request" in event and event["request"].get("url", "").endswith("/health"):
        return None
    return event

┌─────────────────────────────────────────────────────────┐
│  Service Overview                                       │
│  [Error Rate %] [p99 Latency] [Requests/s] [Uptime]    │
├────────────────────────┬────────────────────────────────┤
│  Request Rate          │  Error Rate                    │
│  (by endpoint)         │  (by endpoint, status code)    │
├────────────────────────┼────────────────────────────────┤
│  Latency (p50/p95/p99) │  Active Connections            │
│  (by endpoint)         │  (DB pool, Redis)              │
├────────────────────────┴────────────────────────────────┤
│  Infrastructure                                         │
│  [CPU %] [Memory %] [Disk %] [Network IO]              │
├─────────────────────────────────────────────────────────┤
│  Dependencies                                           │
│  [DB Latency] [Redis Latency] [External API Status]    │
└─────────────────────────────────────────────────────────┘

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