Monitoring Setup

When to Use

Activate this skill when:

•Setting up structured logging for a Python/FastAPI application
•Configuring Prometheus metrics collection and custom counters/histograms
•Implementing health check endpoints (liveness and readiness)
•Designing alert rules and thresholds for production services
•Creating Grafana dashboards for service monitoring
•Integrating Sentry for error tracking and performance monitoring
•Implementing distributed tracing with OpenTelemetry
•Reviewing or improving existing observability coverage

Do NOT use this skill for:

•Responding to active production incidents (use incident-response)
•Deploying monitoring infrastructure (use deployment-pipeline)
•Writing application business logic (use python-backend-expert)
•Docker container configuration (use docker-best-practices)

Instructions

Four Pillars of Observability

Every production service must implement all four pillars.

code

┌─────────────────────────────────────────────────────────────────┐
│                    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        │
└─────────────────────────────────────────────────────────────────┘

Pillar 1: Metrics (Prometheus)

Use the RED method for request-driven services and USE method for resources.

RED Method (for every API endpoint):

•Rate -- Requests per second
•Errors -- Failed requests per second
•Duration -- Request latency distribution

USE Method (for infrastructure resources):

•Utilization -- Percentage of resource used (CPU, memory, disk)
•Saturation -- Work queued or waiting (connection pool, queue depth)
•Errors -- Error events (OOM kills, connection failures)

Key metrics to instrument:

python

from prometheus_client import Counter, Histogram, Gauge, Info

# RED metrics
REQUEST_COUNT = Counter(
    "http_requests_total",
    "Total HTTP requests",
    labelnames=["method", "endpoint", "status_code"],
)

REQUEST_DURATION = Histogram(
    "http_request_duration_seconds",
    "HTTP request duration in seconds",
    labelnames=["method", "endpoint"],
    buckets=[0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0],
)

# USE metrics
DB_POOL_USAGE = Gauge(
    "db_connection_pool_usage",
    "Database connection pool utilization",
    labelnames=["pool_name"],
)

DB_POOL_SIZE = Gauge(
    "db_connection_pool_size",
    "Database connection pool max size",
    labelnames=["pool_name"],
)

REDIS_CONNECTIONS = Gauge(
    "redis_active_connections",
    "Active Redis connections",
)

# Business metrics
ACTIVE_USERS = Gauge(
    "active_users_total",
    "Currently active users",
)

APP_INFO = Info(
    "app",
    "Application metadata",
)

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

See references/metrics-config-template.py for the complete setup.

Pillar 2: Logging (structlog)

Use structured JSON logging with contextual information. Never use print() or unstructured logging in production.

Logging principles:

•Structured -- JSON format, machine-parseable
•Contextual -- Include request ID, user ID, trace ID in every log
•Leveled -- Use appropriate log levels (DEBUG, INFO, WARNING, ERROR, CRITICAL)
•Actionable -- Every WARNING/ERROR log should indicate what to investigate

Log levels and when to use them:

Level	When to Use	Example
DEBUG	Detailed diagnostic info, disabled in production	`Processing item 42 of 100`
INFO	Normal operations, significant events	`User created`, `Payment processed`
WARNING	Unexpected but handled situation	`Retry attempt 2 of 3`, `Cache miss`
ERROR	Operation failed, needs attention	`Database query failed`, `External API timeout`
CRITICAL	System-level failure, immediate action	`Cannot connect to database`, `Out of memory`

structlog setup:

python

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,
)

Adding request context:

python

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

See references/logging-config-template.py for the complete setup.

Pillar 3: Tracing (OpenTelemetry)

Distributed tracing connects logs and metrics across service boundaries.

Trace setup for FastAPI:

python

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()

Custom spans for business logic:

python

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)

Pillar 4: Alerting

Alerts must be actionable. Every alert should indicate what is broken and what to do.

Alert design principles:

•Page only for user-impacting issues -- Do not page for non-urgent warnings
•Set thresholds based on SLOs -- Not arbitrary numbers
•Avoid alert fatigue -- If an alert fires often without action, fix or remove it
•Include runbook links -- Every alert should link to a remediation guide
•Use multi-window burn rates -- Detect issues faster without false positives

Alert thresholds for a typical FastAPI application:

Alert	Condition	Severity	Action
High error rate	`http_requests_total{status=~"5.."}` > 5% of total for 5 min	SEV2	Check logs, consider rollback
High latency	`http_request_duration_seconds` p99 > 2s for 5 min	SEV3	Check DB queries, dependencies
Service down	Health check fails for 2 min	SEV1	Restart, check logs, escalate
DB connections high	Pool usage > 80% for 5 min	SEV3	Check for connection leaks
DB connections critical	Pool usage > 95% for 2 min	SEV2	Restart app, investigate
Memory high	Container memory > 85% for 10 min	SEV3	Check for memory leaks
Disk space low	Disk usage > 85%	SEV3	Clean logs, expand volume
Certificate expiry	SSL cert expires in < 14 days	SEV4	Renew certificate

See references/alert-rules-template.yml for Prometheus alerting rules.

Health Check Endpoints

Every service must expose two health endpoints.

Liveness (/health): Is the process running? Returns 200 if the application is alive.

Readiness (/health/ready): Can the service handle requests? Checks all dependencies.

python

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(),
        },
    )

Error Tracking with Sentry

Sentry captures unhandled exceptions and performance data.

Setup:

python

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

Dashboard Design

Grafana dashboards should follow a consistent layout pattern.

Standard dashboard sections:

•Overview row -- Key SLIs at a glance (error rate, latency, throughput)
•RED metrics row -- Rate, Errors, Duration for each endpoint
•Infrastructure row -- CPU, memory, disk, network
•Dependencies row -- Database, Redis, external API health
•Business metrics row -- Application-specific KPIs

Dashboard layout:

code

┌─────────────────────────────────────────────────────────┐
│  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]    │
└─────────────────────────────────────────────────────────┘

See references/dashboard-template.json for a complete Grafana dashboard template.

Uptime Monitoring

External uptime monitoring validates the service from a user's perspective.

What to monitor externally:

•/health endpoint from multiple geographic regions
•Key user-facing pages (login, dashboard, API docs)
•SSL certificate validity and expiration
•DNS resolution time

Recommended check intervals:

Check	Interval	Timeout	Regions
Health endpoint	30 seconds	10 seconds	3+ regions
Key pages	1 minute	15 seconds	2+ regions
SSL certificate	6 hours	30 seconds	1 region
DNS resolution	5 minutes	5 seconds	3+ regions

Quick Reference

Set up logging:

python

# See references/logging-config-template.py
from app.logging_config import setup_logging
setup_logging(log_level="INFO", json_format=True)

Add Prometheus metrics:

python

# See references/metrics-config-template.py
from app.metrics import setup_metrics
setup_metrics(app)

Configure alerts:

yaml

# See references/alert-rules-template.yml
# Copy to your Prometheus alert rules directory

Create dashboard:

json

// See references/dashboard-template.json
// Import into Grafana via Dashboard -> Import -> Upload JSON

monitoring-setup

Monitoring Setup

When to Use

Instructions

Four Pillars of Observability

Pillar 1: Metrics (Prometheus)

Pillar 2: Logging (structlog)

Pillar 3: Tracing (OpenTelemetry)

Pillar 4: Alerting

Health Check Endpoints

Error Tracking with Sentry

Dashboard Design

Uptime Monitoring

Quick Reference

Monitoring Checklist for New Services