Backend Logging & Log Level Configuration - DeployStack

The DeployStack backend uses Pino logger with Fastify for high-performance, structured logging. This guide covers everything you need to know about configuring and using log levels effectively.

Overview

DeployStack’s logging system is built on industry best practices:

Pino Logger: Ultra-fast JSON logger for Node.js
Fastify Integration: Native logging support with request correlation
Environment-based Configuration: Automatic log level adjustment based on NODE_ENV
Structured Logging: JSON output for production, pretty-printed for development

Available Log Levels

Log levels are ordered by severity (lowest to highest):

Level	Numeric Value	Description	When to Use
`trace`	10	Very detailed debugging	Tracing function calls, variable states
`debug`	20	Debugging information	Development debugging, detailed flow
`info`	30	General information	Important events, startup messages
`warn`	40	Warning messages	Recoverable errors, deprecation notices
`error`	50	Error conditions	Caught exceptions, failed operations
`fatal`	60	Fatal errors	Unrecoverable errors, application crashes

Configuration

Environment Variables

Set the log level using the LOG_LEVEL environment variable:

# Development - show debug information
LOG_LEVEL=debug npm run dev

# Production - show info and above
LOG_LEVEL=info npm run start

# Troubleshooting - show everything
LOG_LEVEL=trace npm run dev

# Quiet mode - only errors and fatal
LOG_LEVEL=error npm run start

Default Behavior

The logger automatically adjusts based on your environment:

// From src/fastify/config/logger.ts
export const loggerConfig: FastifyServerOptions['logger'] = {
  level: process.env.LOG_LEVEL || (process.env.NODE_ENV === 'production' ? 'info' : 'debug'),
  transport: process.env.NODE_ENV !== 'production'
    ? {
        target: 'pino-pretty',
        options: {
          colorize: true,
          translateTime: 'SYS:standard',
          ignore: 'pid,hostname'
        }
      }
    : undefined
}

Default Levels:

Development: debug (shows debug, info, warn, error, fatal)
Production: info (shows info, warn, error, fatal)

Log Output Formats

Development Format (Pretty-printed)

[2025-07-03 10:48:06.636 +0200] INFO: ✅ Database initialization completed
[2025-07-03 10:48:06.640 +0200] DEBUG: 🔄 Starting global settings initialization...
[2025-07-03 10:48:06.645 +0200] ERROR: ❌ Failed to connect to external service

Production Format (JSON)

{"level":30,"time":"2025-07-03T08:48:06.636Z","pid":1234,"hostname":"server","msg":"Database initialization completed"}
{"level":20,"time":"2025-07-03T08:48:06.640Z","pid":1234,"hostname":"server","msg":"Starting global settings initialization..."}
{"level":50,"time":"2025-07-03T08:48:06.645Z","pid":1234,"hostname":"server","msg":"Failed to connect to external service"}

Logger Parameter Injection Pattern

DeployStack follows a consistent pattern for passing logger instances to services and utilities. This ensures proper structured logging throughout the application while maintaining the Fastify logger chain for request correlation.

✅ DO: Pass Logger as Parameter to Services

// ✅ Good - Services accept logger as parameter
class EmailService {
  static async sendEmail(options: SendEmailOptions, logger: FastifyBaseLogger): Promise<EmailSendResult> {
    logger.debug({
      operation: 'send_email',
      recipient: options.to,
      template: options.template
    }, 'Sending email');
    
    try {
      // ... email sending logic
      logger.info({
        operation: 'send_email',
        messageId: result.messageId,
        recipients: result.recipients
      }, 'Email sent successfully');
      
      return result;
    } catch (error) {
      logger.error({
        operation: 'send_email',
        error,
        recipient: options.to,
        template: options.template
      }, 'Failed to send email');
      throw error;
    }
  }
}

// ✅ Good - Database functions accept logger parameter
export async function initializeDatabase(logger: FastifyBaseLogger): Promise<boolean> {
  logger.info({
    operation: 'initialize_database'
  }, 'Database initialization started');
  
  try {
    // ... database initialization logic
    logger.info({
      operation: 'initialize_database'
    }, 'Database initialized successfully');
    return true;
  } catch (error) {
    logger.error({
      operation: 'initialize_database',
      error
    }, 'Failed to initialize database');
    return false;
  }
}

✅ DO: Pass Logger from Calling Context

// ✅ Good - Pass logger from server context
await initializeDatabase(server.log);

// ✅ Good - Pass logger from request context in routes
server.post('/api/send-email', async (request, reply) => {
  const result = await EmailService.sendEmail(emailOptions, request.log);
  return result;
});

// ✅ Good - Pass logger in plugin initialization
await pluginManager.initializePlugins(server.log);

✅ DO: Use Child Loggers for Persistent Context

// ✅ Good - Create child logger with persistent context
class UserService {
  static async processUser(userId: string, logger: FastifyBaseLogger) {
    const childLogger = logger.child({ userId, service: 'UserService' });
    
    childLogger.debug('Starting user processing');
    childLogger.info('User data retrieved');
    childLogger.debug('Processing completed');
  }
}

❌ DON’T: Create Separate Logger Utilities

// ❌ Bad - Don't create separate logger utility files
// utils/logger.ts
export const logger = createLogger();

// ❌ Bad - Don't import logger utilities in services
import { logger } from '../utils/logger';

class SomeService {
  static async doSomething() {
    logger.info('This bypasses the Fastify logger chain');
  }
}

❌ DON’T: Use console.* in Services

// ❌ Bad - console.* bypasses the logging system
class DatabaseService {
  static async connect() {
    console.log('Connecting to database...'); // No structured logging
    console.error('Connection failed:', error); // No context objects
  }
}

// ✅ Good - Use passed logger parameter
class DatabaseService {
  static async connect(logger: FastifyBaseLogger) {
    logger.info({
      operation: 'database_connect'
    }, 'Connecting to database...');
    
    logger.error({
      operation: 'database_connect',
      error,
      connectionString: config.url
    }, 'Connection failed');
  }
}

Developer Best Practices

✅ DO: Use Proper Log Levels

// ✅ Good - Use appropriate log levels
server.log.debug('🔄 Starting database initialization...');
server.log.info('✅ Database connection established');
server.log.warn('⚠️ Using fallback configuration');
server.log.error('❌ Failed to process request:', error);
server.log.fatal('💀 Critical system failure:', error);

❌ DON’T: Use Manual Prefixes

// ❌ Bad - Manual prefixes defeat the purpose
server.log.info('🔄 [DEBUG] Starting database initialization...');
server.log.info('✅ [INFO] Database connection established');

// ✅ Good - Use proper log levels instead
server.log.debug('🔄 Starting database initialization...');
server.log.info('✅ Database connection established');

✅ DO: Use the Fastify Logger

// ✅ Good - Use server.log for consistent formatting
server.log.info('User authenticated successfully');

// ❌ Bad - console.log bypasses the logging system
console.log('User authenticated successfully');

✅ DO: Add Context Objects

Context objects make your logs searchable, filterable, and much more useful for debugging. Always include relevant context that helps identify what happened, where, and to whom.

// ✅ Good - Structured logging with context
server.log.info({
  userId: 'user123',
  action: 'login',
  ipAddress: '192.168.1.1',
  userAgent: 'Mozilla/5.0...',
  operation: 'user_authentication'
}, 'User login successful');

// ✅ Good - Error logging with full context
server.log.error({
  error: err,
  userId: 'user123',
  operation: 'database_query',
  table: 'users',
  queryType: 'SELECT'
}, 'Database operation failed');

// ✅ Good - Service operations with context
server.log.debug({
  recipient: 'user@example.com',
  template: 'welcome',
  messageId: 'abc123',
  operation: 'send_email'
}, 'Email sent successfully');

// ✅ Good - API operations with context
server.log.warn({
  endpoint: '/api/users',
  method: 'POST',
  statusCode: 429,
  clientIp: '192.168.1.1',
  operation: 'rate_limit_exceeded'
}, 'Rate limit exceeded for client');

Best Practices for Context Objects:

Always include operation: A consistent field that describes what operation was being performed
Add identifiers: Include relevant IDs (userId, orderId, sessionId, etc.) for easy filtering
Include request context: IP addresses, user agents, request IDs for web requests
Add timing information: Duration, timestamps, or performance metrics when relevant
Use consistent naming: Stick to camelCase and consistent field names across your application

Examples of Good Context Properties:

operation: What was happening (e.g., ‘send_email’, ‘user_login’, ‘database_query’)
userId, sessionId, requestId: Identifiers for tracking
duration, responseTime: Performance metrics
statusCode, method, endpoint: HTTP-related context
table, queryType: Database-related context
recipient, template, messageId: Email-related context

✅ DO: Use Child Loggers for Context

// ✅ Good - Child logger with persistent context
function processUser(userId: string) {
  const childLogger = server.log.child({ userId });
  
  childLogger.debug('Starting user processing');
  childLogger.info('User data retrieved');
  childLogger.debug('Processing completed');
}

Common Logging Patterns

Database Operations

// Database initialization
server.log.debug('🔄 Initializing database connection...');
server.log.info('✅ Database connected successfully');

// Query operations
server.log.debug('Executing user query', { userId, query: 'SELECT * FROM users' });
server.log.warn('Slow query detected', { duration: '2.5s', query: 'complex_query' });

Authentication & Security

// Authentication events
server.log.info('User login attempt', { email: user.email, ipAddress });
server.log.warn('Failed login attempt', { email, ipAddress, reason: 'invalid_password' });
server.log.error('Security violation detected', { ipAddress, action: 'brute_force' });

API Requests

// Request processing (handled automatically by Fastify)
// Custom business logic logging
server.log.debug('Processing payment request', { amount, currency, userId });
server.log.info('Payment processed successfully', { transactionId, amount });
server.log.error('Payment failed', { error, userId, amount });

Plugin System

// Plugin lifecycle
server.log.debug('Loading plugin', { pluginId, version });
server.log.info('Plugin loaded successfully', { pluginId });
server.log.warn('Plugin deprecated', { pluginId, deprecationDate });
server.log.error('Plugin failed to load', { pluginId, error });

Fixing Console.log Issues

Important: Replace all console.log statements with proper Pino logger calls to ensure consistent formatting and log level filtering.

Problem: Inconsistent Log Output

// ❌ Problem - Mixed logging approaches
console.log('✅ [GlobalSettingsInitService] Operation completed');  // No timestamp
server.log.info('✅ Database initialization completed');             // With timestamp

Solution: Use Proper Logger

// ✅ Solution - Consistent logging
class GlobalSettingsInitService {
  private static logger = server.log.child({ service: 'GlobalSettingsInitService' });
  
  static async loadSettings() {
    this.logger.debug('Loading settings definitions...');
    this.logger.info('Settings loaded successfully');
  }
}

Passing Logger to Classes

// ✅ Good - Pass logger instance to classes
class PluginManager {
  constructor(private logger: FastifyBaseLogger) {}
  
  async loadPlugin(pluginId: string) {
    this.logger.debug('Loading plugin', { pluginId });
    this.logger.info('Plugin loaded successfully', { pluginId });
  }
}

// Usage
const pluginManager = new PluginManager(server.log.child({ component: 'PluginManager' }));

Environment-Specific Configuration

Development Environment

# .env file for development
NODE_ENV=development
LOG_LEVEL=debug

Features:

Pretty-printed, colorized output
Shows debug and trace information
Includes timestamps and emojis
Easier to read during development

Production Environment

# Production environment variables
NODE_ENV=production
LOG_LEVEL=info

Features:

Structured JSON output
Optimized for log aggregation
Excludes debug information
Better performance

Testing Environment

# Testing environment
NODE_ENV=test
LOG_LEVEL=error

Features:

Minimal log output during tests
Only shows errors and fatal messages
Reduces test noise

Troubleshooting

Debug Mode Not Working

If debug logs aren’t showing:

Check LOG_LEVEL: Ensure it’s set to debug or trace
Check NODE_ENV: Development mode enables debug by default
Restart Server: Environment changes require restart

# Force debug mode
LOG_LEVEL=debug npm run dev

Performance Issues

If logging is impacting performance:

Increase Log Level: Use info or warn in production
Remove Debug Logs: Clean up excessive debug statements
Use Async Logging: Pino handles this automatically

Log Aggregation

For production log management:

// Add correlation IDs for request tracking
server.addHook('onRequest', async (request) => {
  request.log = request.log.child({ 
    requestId: request.id,
    userAgent: request.headers['user-agent']
  });
});

Migration Guide

From Manual Prefixes

// Before
server.log.info('🔄 [DEBUG] Starting operation...');
server.log.info('✅ [INFO] Operation completed');
server.log.info('❌ [ERROR] Operation failed');

// After
server.log.debug('🔄 Starting operation...');
server.log.info('✅ Operation completed');
server.log.error('❌ Operation failed');

From Console.log

// Before
console.log('User logged in:', userId);
console.error('Database error:', error);

// After
server.log.info('User logged in', { userId });
server.log.error('Database error', { error, userId });

Summary

Use proper log levels instead of manual prefixes
Replace console.log with server.log for consistency
Add structured context to make logs searchable
Configure LOG_LEVEL via environment variables
Use child loggers for persistent context
Follow the patterns shown in this guide

With proper log level configuration, you’ll have a production-ready logging system that scales from development to enterprise deployments.

​Overview

​Available Log Levels

​Configuration

​Environment Variables

​Default Behavior

​Log Output Formats

​Development Format (Pretty-printed)

​Production Format (JSON)

​Logger Parameter Injection Pattern

​✅ DO: Pass Logger as Parameter to Services

​✅ DO: Pass Logger from Calling Context

​✅ DO: Use Child Loggers for Persistent Context

​❌ DON’T: Create Separate Logger Utilities

​❌ DON’T: Use console.* in Services

​Developer Best Practices

​✅ DO: Use Proper Log Levels

​❌ DON’T: Use Manual Prefixes

​✅ DO: Use the Fastify Logger

​✅ DO: Add Context Objects

​✅ DO: Use Child Loggers for Context

​Common Logging Patterns

​Database Operations

​Authentication & Security

​API Requests

​Plugin System

​Fixing Console.log Issues

​Problem: Inconsistent Log Output

​Solution: Use Proper Logger

​Passing Logger to Classes

​Environment-Specific Configuration

​Development Environment

​Production Environment

​Testing Environment

​Troubleshooting

​Debug Mode Not Working

​Performance Issues

​Log Aggregation

​Migration Guide

​From Manual Prefixes

​From Console.log

​Summary

Overview

Available Log Levels

Configuration

Environment Variables

Default Behavior

Log Output Formats

Development Format (Pretty-printed)

Production Format (JSON)

Logger Parameter Injection Pattern

✅ DO: Pass Logger as Parameter to Services

✅ DO: Pass Logger from Calling Context

✅ DO: Use Child Loggers for Persistent Context

❌ DON’T: Create Separate Logger Utilities

❌ DON’T: Use console.* in Services

Developer Best Practices

✅ DO: Use Proper Log Levels

❌ DON’T: Use Manual Prefixes

✅ DO: Use the Fastify Logger

✅ DO: Add Context Objects

✅ DO: Use Child Loggers for Context

Common Logging Patterns

Database Operations

Authentication & Security

API Requests

Plugin System

Fixing Console.log Issues

Problem: Inconsistent Log Output

Solution: Use Proper Logger

Passing Logger to Classes

Environment-Specific Configuration

Development Environment

Production Environment

Testing Environment

Troubleshooting

Debug Mode Not Working

Performance Issues

Log Aggregation

Migration Guide

From Manual Prefixes

From Console.log

Summary