Logging Best Practices

Structured Logging

• Use structured logging formats (JSON) for all log output
• Include consistent fields across all log entries
• Make logs machine-parseable while remaining human-readable
• Use a logging library that supports structured output natively
• Avoid string concatenation for log messages; use structured fields

Standard Log Fields

• timestamp: ISO 8601 format with timezone
• level: Log severity (DEBUG, INFO, WARN, ERROR, FATAL)
• message: Human-readable description of the event
• service: Name of the service or application
• version: Application version or build identifier
• trace_id: Distributed tracing correlation ID
• span_id: Current span identifier
• request_id: Unique identifier for the request

Log Levels

• DEBUG: Detailed diagnostic information for development
• INFO: Normal operational events and state changes
• WARN: Unexpected situations that are handled gracefully
• ERROR: Failures that affect current operation but not the service
• FATAL: Critical failures requiring immediate attention

Context Propagation

• Include request context in all log entries within a request lifecycle
• Propagate trace IDs across service boundaries
• Add user context (anonymized) for user-initiated actions
• Include relevant business context for domain events
• Use MDC (Mapped Diagnostic Context) or equivalent for context management

Security and Privacy

• Never log sensitive information (passwords, tokens, PII)
• Mask or redact sensitive data when it must be referenced
• Implement log access controls appropriate to data sensitivity
• Consider data retention policies and compliance requirements
• Audit log access for sensitive systems

Performance Considerations

• Use asynchronous logging to avoid blocking application threads
• Implement log sampling for high-volume debug logs in production
• Buffer logs appropriately to balance latency and throughput
• Monitor logging infrastructure for bottlenecks
• Set appropriate log levels per environment

Log Aggregation

• Centralize logs from all services into a single platform
• Use consistent formatting across all services
• Implement log rotation and retention policies
• Enable full-text search and filtering capabilities
• Set up log-based alerts for critical patterns

Error Logging

• Include full error context: message, code, stack trace
• Log the chain of errors in wrapped/nested exceptions
• Include relevant request and state information
• Avoid duplicate error logging across layers
• Log error recovery actions and outcomes

Best Practices

• Log at service boundaries (entry and exit points)
• Include timing information for performance analysis
• Log configuration changes and deployments
• Create actionable log messages that aid debugging
• Review and clean up logging regularly to reduce noise

Log Message Guidelines

• Write clear, descriptive messages
• Include relevant identifiers (user ID, order ID, etc.)
• Avoid generic messages like "Error occurred"
• Use consistent terminology across the application
• Include enough context to understand the event without additional lookups

Environment-Specific Configuration

• Development: DEBUG level, console output, verbose formatting
• Staging: INFO level, structured JSON, full context
• Production: INFO/WARN level, structured JSON, sampling for DEBUG