Log4j and log stitching in distributed Java systems: correlating logs across multiple services

18 Sep 2023

In a distributed Java system, it is common to have multiple services working together to deliver a seamless experience to users. However, when an issue arises and you need to troubleshoot, it can be challenging to correlate logs across different services. This is where Log4j and log stitching come into play.

Introducing Log4j

Log4j is a popular logging framework for Java applications. It allows developers to log messages of different severity levels, such as DEBUG, INFO, WARN, ERROR, and FATAL. These logs provide valuable insights into the system’s behavior and help identify and solve issues.

The Need for Log Stitching

In a distributed system, each service typically logs independently. When an error occurs, it’s essential to trace the flow of a request across different services to understand the root cause. This is where log stitching comes in handy. Log stitching enables you to correlate logs from multiple services by analyzing and linking related log entries based on contextual information.

Implementing Log Stitching with Log4j

To implement log stitching with Log4j, you need to follow these steps:

Define correlation IDs: Generate and assign a unique correlation ID to each request or transaction that flows through the system. This ID acts as a common identifier across service boundaries.
Inject correlation IDs: Within each service, you need to inject the correlation ID into every log entry. This can be achieved by modifying the log format or by using a logging library that supports correlation ID injection, such as Log4j’s MDC (Mapped Diagnostic Context).
```
 // Example of injecting a correlation ID with Log4j's MDC
 import org.apache.log4j.MDC;
    
 // Set correlation ID in the MDC
 MDC.put("correlationId", "12345");
    
 // Log a message
 logger.info("Processing request");
```
Extract and correlate logs: After the logs are generated, you can use log aggregation and analysis tools like ELK stack (Elasticsearch, Logstash, and Kibana) or Splunk to extract and correlate the logs based on the injected correlation IDs. These tools provide powerful search and data visualization capabilities, allowing you to gain insights into the entire flow of a request across multiple services.

Benefits of Log Stitching

Log stitching offers several benefits for troubleshooting in distributed Java systems:

Seamless log correlation: By injecting correlation IDs into each log entry, you can easily correlate logs across different services, enabling more efficient debugging and issue identification.
Improved troubleshooting: Log stitching gives you a holistic view of application behavior, allowing you to trace the flow of requests and identify bottlenecks or abnormalities.
Reduced mean time to resolution: With correlated logs, you can pinpoint the root cause of an issue faster, leading to quicker resolution and improved system uptime.

Conclusion

Log4j and log stitching provide essential tools for correlating logs in distributed Java systems. By implementing log stitching techniques and leveraging log aggregation and analysis tools, you can gain valuable insights into the behavior of your distributed system, leading to improved troubleshooting and faster issue resolution.

#log4j #logstitching