Logging is a technique used in software development that allows developers to see into their application's runtime process. Logging can be used for various purposes, including performance monitoring and debugging. Debug logging is most often used in the development phase of software, as it sometimes exposes too much information and is too verbose for production workloads.

In this article, we’ll define debug logging, along with its benefits in the software development process. We’ll also explore the best practices for getting the most out of debug logging to reduce noise and protect sensitive data from being leaked.

What Is Debug Logging?

Generally speaking, logging in software applications involves recording events, errors, and other relevant information during the execution of a software application or process. Different types of logging include audit logging (for recording security-related events), performance logging (for capturing information related to an application’s performance), and event logging (to record specific occurrences of events like user actions or system changes).

Among the different kinds of logging is debug logging, which helps developers diagnose application problems and errors. Debug logging specifically focuses on providing information to assist in identifying and resolving bugs or defects.

Debug logging is typically enabled for the development and testing stages of software — but not production — because of the log message size and quantity that is often generated for debugging. The amount of log data is necessary to track down the root cause of bugs when software is still in development. However, in the production phase, this much log data can be a hindrance to effective querying for non-debugging purposes.

Benefits of Debug Logging

By capturing and storing information about the application's execution at runtime, debug logging yields many benefits for developers:

• Assistance in identifying root cause: When an error or unexpected behavior occurs, developers can examine the log files to understand what happened and identify the root cause of the issue. Debug logging can provide a wealth of information about the application's state at the time of the error, including the values of variables, the state of the system, and the sequence of events that led to the error.
• Insight into how to fix an error: Just as debug logging information helps isolate the root cause of an error, that same information provides insights into how developers can implement a fix.
• Insight into how to reproduce an error: When edge cases are hit during runtime, the information gleaned from debug logging can make reproducing issues easier.
• Early identification of potential performance errors: By logging data during runtime, developers can better understand an application's performance and identify potential bottlenecks or areas for optimization.

Best Practices for Debug Logging

The following best practices can help you get the most out of your logs while debug logging. They can also protect against compromising sensitive data in your application log files.

Choose the Right Log Level

By setting the log level appropriately, developers can filter out irrelevant information and focus on what's important. The following log levels are common to most programming languages and frameworks:

• Debug: Used in the development process to show diagnostic information about the application.
• Info: Provides information about what is part of an application’s regular operation, such as a successful system startup or shutdown.
• Warning: Indicates runtime issues that do not result in an error, but may show other problems that could eventually result in an error, such as system instability or connectivity issues.
• Error: Shows runtime issues that violate the requirements of an application, such as unhandled input or outputs to the process.
• Critical: Similar to error log messages, critical levels are for events that violate the application’s requirements such that they will generally result in the shutdown of the application.

Remember, setting the log level too low can result in missing important information; putting it too high can generate excessive noise, making it harder to find essential logs and slowing down the system.

Generate Diagnostic Information

When debug logging, you will want to generate further diagnostic information to make it easier to understand how your application is running. Some of these diagnostic indicators can include:

• Timestamps of events
• Trace IDs or session IDs for distributed applications
• Resource usage
• Received data from external services

With this information, a developer can analyze a software application's behavior more effectively. However, during a production workload, it may not be necessary to output this level of information to reduce noise from log files.

Protect Sensitive Log Data

When debug logging, it is essential to protect sensitive information. Protecting sensitive data can include not logging personal identifying information (PII). Or if this data must be logged, developers should make sure that the data is appropriately secured through log file permissions or securely shipped to an external log repository.

Set up log file rotation to retain log files on a host only as long as required. Also, protect your log data by having your software processes log to separate log files or directories, so the appropriate permissions and access controls can be applied to the log files. Then, provide users or machine processes with the appropriate access based on the principle of least privilege.

Conclusion

By using debug logging, developers can inspect how their applications perform, identify bugs and errors, and deeply analyze the behavior of their software. In this article, we explored debug logging, along with its benefits in the development process. By following the best practices of debug logging, you can ensure that your debug logs serve your software development process and increase the productivity of your development team.

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