Logging for backend engineers

Plan Before Implementing Logging

• Define a clear strategy before adding logging to your application.

• Identify key performance indicators (KPIs) to track for monitoring and debugging.

Use Different Log Levels

• Info: Normal operations (e.g., successful login).

• Warning: Potential issues (e.g., slow payment processing).

• Error: Serious problems (e.g., database failure).

• Fatal: Critical system failures (e.g., out of memory).

• Dynamically adjust verbosity levels when debugging to avoid excessive logging.

Structured Logging

• Instead of plain text logs, use structured formats like JSON or XML for better searchability and filtering.

Add Context to Logs

• Provide information about who did what and when.

• Example:

    { 
      "event": "update_test", 
      "user_id": 11001, 
      "test_id": 30023, 
      "change": { "question_count": { "from": 120, "to": 90 } }, 
      "timestamp": "2025-03-04T10:20:00Z"
    }
  

• Another example for a file upload failure:

    { 
      "event": "file_upload_failed", 
      "user": "user456", 
      "file": "report.pdf", 
      "error": "File too large", 
      "timestamp": "2025-03-04T10:20:00Z"
    }
  

Log Sampling

• Instead of logging every instance of non-critical activities (e.g., login attempts), use sampling.

• Example: Log only every 2 out of 10 login attempts instead of logging all.

Summarize Logs Instead of Logging Each Step

• Instead of logging every individual step, consolidate logs into meaningful summaries.

• Example of inefficient logging:

    User requested profile page  
    Fetched user details  
    Rendered profile page
  

• Improved version:

    { 
      "event": "profile_page_load", 
      "user": "user789", 
      "status": "success", 
      "duration_ms": 120 
    }
  

• If an error occurs while fetching user details, provide a clear error log with relevant details.

Use Centralized Logging

• Instead of keeping separate logs for each microservice, use a centralized logging system for better correlation and monitoring.

Set Retention Policies

• Define different retention periods for logs:

  • Error logs: Retain for 1 month.

  • Security logs: Retain for 6 months.

  • Older logs should be moved to cold storage after the retention period.

Secure Log Transmission & Storage

• Encrypt logs when transmitting and storing them to prevent unauthorized access.

Avoid Logging Sensitive Data