Platxa Logging

Name: platxa-logging
Rating: 92
Author: platxa

Guide for structured logging and correlation ID patterns across Platxa services.

Overview

Language	Logger	Correlation	Output Format
Python	logging module	ContextVar	JSON (audit)
TypeScript	Console	Session ID	Text/JSON
Go	log/slog	context.Context	JSON

Core Principles

•Structured Over Unstructured: JSON format for machine parsing and log aggregation
•Correlation Required: Every request gets a unique ID, propagated across all services
•Context Propagation: Thread/goroutine-safe context passing
•Consistent Field Keys: Standardized keys across all languages
•Log Levels by Impact: ERROR=failed, WARN=degraded, INFO=normal, DEBUG=diagnostic

Standard Field Keys

Key	Type	Description
`timestamp`	ISO8601	When event occurred
`level`	string	error/warn/info/debug
`message`	string	Human-readable description
`request_id`	string	Correlation ID (UUID)
`namespace`	string	K8s namespace (instance-xxx)
`service`	string	Service name
`duration_ms`	int	Operation duration in milliseconds
`error`	string	Error message (if any)
`user_id`	int	User identifier (if authenticated)

Correlation ID Patterns

HTTP Header Propagation

code

Client → Service A → Service B → Service C
         │            │            │
         └─ X-Request-ID: abc123 ─┘

Header Name: X-Request-ID (primary) or X-Correlation-ID

Generation Rules

•At Service Boundary: Generate if header missing
•Format: UUID v4 (550e8400-e29b-41d4-a716-446655440000)
•Propagate: Include in all downstream requests
•Log: Include in every log entry

Python Implementation

python

import uuid
from contextvars import ContextVar

# Thread-safe storage
request_id: ContextVar[str] = ContextVar('request_id', default='')

def get_request_id() -> str:
    """Get current request ID or generate new one."""
    rid = request_id.get()
    return rid if rid else str(uuid.uuid4())

def set_request_id(rid: str) -> None:
    """Set request ID for current context."""
    request_id.set(rid)

# Flask/Werkzeug middleware
@app.before_request
def extract_request_id():
    rid = request.headers.get('X-Request-ID', str(uuid.uuid4()))
    set_request_id(rid)
    g.request_id = rid

@app.after_request
def add_request_id_header(response):
    response.headers['X-Request-ID'] = get_request_id()
    return response

Go Implementation

type contextKey string

const RequestIDKey contextKey = "request_id"

func RequestIDMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        reqID := r.Header.Get("X-Request-ID")
        if reqID == "" {
            reqID = uuid.New().String()
        }
        ctx := context.WithValue(r.Context(), RequestIDKey, reqID)
        w.Header().Set("X-Request-ID", reqID)
        next.ServeHTTP(w, r.WithContext(ctx))
    })
}

func GetRequestID(ctx context.Context) string {
    if reqID, ok := ctx.Value(RequestIDKey).(string); ok {
        return reqID
    }
    return ""
}

TypeScript Implementation

typescript

import { v4 as uuidv4 } from 'uuid';

interface RequestContext {
  requestId: string;
  sessionId: string;
  userId?: string;
}

// Express middleware
function requestIdMiddleware(req: Request, res: Response, next: NextFunction) {
  const requestId = req.headers['x-request-id'] as string || uuidv4();
  req.context = { requestId, sessionId: req.sessionID };
  res.setHeader('X-Request-ID', requestId);
  next();
}

// Fetch wrapper for downstream calls
async function fetchWithCorrelation(url: string, ctx: RequestContext, options = {}) {
  return fetch(url, {
    ...options,
    headers: {
      ...options.headers,
      'X-Request-ID': ctx.requestId,
    },
  });
}

Structured Logging

JSON Output Format

json

{
  "timestamp": "2024-01-15T10:30:45.123Z",
  "level": "info",
  "message": "request completed",
  "request_id": "550e8400-e29b-41d4-a716-446655440000",
  "namespace": "instance-abc123xy",
  "service": "waking-service",
  "duration_ms": 45,
  "method": "GET",
  "path": "/api/status",
  "status": 200
}

Python Structured Logger

python

import logging
import json
from datetime import datetime

class StructuredFormatter(logging.Formatter):
    """JSON formatter with correlation ID."""

    def format(self, record: logging.LogRecord) -> str:
        log_entry = {
            'timestamp': datetime.utcnow().isoformat() + 'Z',
            'level': record.levelname.lower(),
            'message': record.getMessage(),
            'logger': record.name,
            'request_id': get_request_id(),
        }

        # Add extra fields
        if hasattr(record, 'namespace'):
            log_entry['namespace'] = record.namespace
        if hasattr(record, 'duration_ms'):
            log_entry['duration_ms'] = record.duration_ms
        if record.exc_info:
            log_entry['exception'] = self.formatException(record.exc_info)

        return json.dumps(log_entry)

# Setup
handler = logging.StreamHandler()
handler.setFormatter(StructuredFormatter())
logging.root.addHandler(handler)

Go slog Setup

import (
    "log/slog"
    "os"
)

// Field key constants
const (
    KeyRequestID  = "request_id"
    KeyNamespace  = "namespace"
    KeyDurationMS = "duration_ms"
    KeyError      = "error"
    KeyService    = "service"
)

func SetupLogger(level string, jsonFormat bool) {
    opts := &slog.HandlerOptions{Level: parseLevel(level)}

    var handler slog.Handler
    if jsonFormat {
        handler = slog.NewJSONHandler(os.Stdout, opts)
    } else {
        handler = slog.NewTextHandler(os.Stdout, opts)
    }

    slog.SetDefault(slog.New(handler))
}

// Usage with context
func LogWithContext(ctx context.Context, msg string, args ...any) {
    allArgs := append([]any{KeyRequestID, GetRequestID(ctx)}, args...)
    slog.Info(msg, allArgs...)
}

TypeScript Logger

typescript

interface LogEntry {
  timestamp: string;
  level: 'error' | 'warn' | 'info' | 'debug';
  message: string;
  requestId?: string;
  [key: string]: unknown;
}

class StructuredLogger {
  constructor(private service: string, private context?: RequestContext) {}

  private log(level: LogEntry['level'], message: string, data?: Record<string, unknown>) {
    const entry: LogEntry = {
      timestamp: new Date().toISOString(),
      level,
      message,
      service: this.service,
      requestId: this.context?.requestId,
      ...data,
    };

    if (level === 'error') {
      console.error(JSON.stringify(entry));
    } else {
      console.log(JSON.stringify(entry));
    }
  }

  info(message: string, data?: Record<string, unknown>) { this.log('info', message, data); }
  warn(message: string, data?: Record<string, unknown>) { this.log('warn', message, data); }
  error(message: string, data?: Record<string, unknown>) { this.log('error', message, data); }
  debug(message: string, data?: Record<string, unknown>) { this.log('debug', message, data); }
}

Log Level Guidelines

Level	When to Use	Example
ERROR	Operation failed, requires attention	`"database connection failed"`
WARN	Degraded but working, potential issue	`"rate limit at 80%"`
INFO	Normal operation, significant events	`"instance started"`
DEBUG	Diagnostic detail, development	`"parsing config file"`

Dynamic Log Levels (Go)

func LoggingMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        start := time.Now()
        wrapped := &responseWriter{ResponseWriter: w}

        next.ServeHTTP(wrapped, r)

        // Dynamic level based on status
        level := slog.LevelInfo
        if wrapped.statusCode >= 500 {
            level = slog.LevelError
        } else if wrapped.statusCode >= 400 {
            level = slog.LevelWarn
        }

        slog.Log(r.Context(), level, "http request",
            KeyRequestID, GetRequestID(r.Context()),
            "method", r.Method,
            "path", r.URL.Path,
            "status", wrapped.statusCode,
            KeyDurationMS, time.Since(start).Milliseconds(),
        )
    })
}

Workflow

Step 1: Add Correlation ID Middleware

Language	Implementation
Python	Flask `@app.before_request` with ContextVar
Go	`RequestIDMiddleware` with context.Context
TypeScript	Express middleware with request augmentation

Step 2: Configure Structured Logger

•Create JSON formatter
•Add request ID to all log entries
•Define standard field keys
•Set appropriate log levels

Step 3: Propagate to Downstream Services

python

# Python - httpx/requests
response = requests.post(url, headers={'X-Request-ID': get_request_id()})

# Go - http.Client
req.Header.Set("X-Request-ID", GetRequestID(ctx))

# TypeScript - fetch
fetch(url, { headers: { 'X-Request-ID': context.requestId } })

Step 4: Query Logs by Correlation ID

bash

# Loki query
{namespace="instance-abc123"} |= "request_id=550e8400"

# grep
grep "550e8400" /var/log/service/*.log

Examples

Example 1: Python API with Correlation

python

import logging
from flask import Flask, request, g

app = Flask(__name__)
_logger = logging.getLogger(__name__)

@app.before_request
def setup_correlation():
    g.request_id = request.headers.get('X-Request-ID', str(uuid.uuid4()))
    set_request_id(g.request_id)

@app.route('/api/provision', methods=['POST'])
def provision():
    _logger.info("Provisioning instance", extra={
        'namespace': request.json.get('namespace'),
        'action': 'provision'
    })

    # Call downstream service
    response = requests.post(
        f"{VALIDATOR_URL}/validate",
        headers={'X-Request-ID': g.request_id},
        json=request.json
    )

    return jsonify({'status': 'ok'})

Example 2: Go Service Handler

func (h *Handler) HandleWake(w http.ResponseWriter, r *http.Request) {
    ctx := r.Context()
    namespace := chi.URLParam(r, "namespace")

    slog.Info("wake request received",
        KeyRequestID, GetRequestID(ctx),
        KeyNamespace, namespace,
    )

    start := time.Now()
    err := h.scaler.WakeInstance(ctx, namespace)

    if err != nil {
        slog.Error("wake failed",
            KeyRequestID, GetRequestID(ctx),
            KeyNamespace, namespace,
            KeyError, err,
            KeyDurationMS, time.Since(start).Milliseconds(),
        )
        http.Error(w, "Failed to wake instance", http.StatusServiceUnavailable)
        return
    }

    slog.Info("wake completed",
        KeyRequestID, GetRequestID(ctx),
        KeyNamespace, namespace,
        KeyDurationMS, time.Since(start).Milliseconds(),
    )

    w.WriteHeader(http.StatusOK)
}

Example 3: Audit Logging (Python)

python

_audit_logger = logging.getLogger('instance_manager.audit')

def _audit_log(self, action: str, resource_type: str, resource_name: str,
               result: str = 'success', details: dict = None):
    """Create structured audit log entry."""
    log_entry = {
        'timestamp': datetime.now().isoformat(),
        'request_id': get_request_id(),
        'action': action,
        'resource_type': resource_type,
        'resource_name': resource_name,
        'result': result,
        'user_id': self.env.user.id,
        'user_name': self.env.user.name,
        'details': details,  # Never include secrets!
    }
    _audit_logger.info(json.dumps(log_entry))

Troubleshooting

Issue	Cause	Fix
Missing request ID	Middleware not installed	Add correlation middleware first
ID not propagating	Forgot header in downstream call	Add X-Request-ID to all requests
Duplicate IDs	Generating instead of reusing	Check header before generating
Lost context (Python)	Thread boundary	Use ContextVar, not threading.local
Lost context (Go)	Not passing ctx	Always pass context.Context
JSON parse errors	Non-JSON in logs	Ensure all loggers use JSON formatter
Missing fields	Not using extra/attrs	Add fields via extra (Python) or args (Go)

Output Checklist

After implementing logging:

• Correlation ID middleware installed
• All log entries include request_id
• JSON format for production logs
• Standard field keys used consistently
• Downstream calls propagate X-Request-ID
• Log levels match severity guidelines
• Audit logs include user context
• No secrets in log output
• Logs queryable by correlation ID

Related Resources

•Correlation IDs: See references/correlation-ids.md
•Structured Logging: See references/structured-logging.md
•Language Patterns: See references/language-patterns.md