Enhance Visibility Into Reactor FlatMap

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Description

In modern web applications, it's not uncommon to see multiple service calls chained together to fetch data from various sources. This is where Reactor Netty comes into play, providing a powerful toolkit for building reactive systems. However, as applications grow in complexity, visibility into these systems becomes increasingly important. A customer is currently experiencing a visibility gap in their Reactor Netty-based applications, where the instrumentation only captures the first HTTP call, while subsequent calls within Mono.flatMap are labeled "No Deeper Visibility". This article will delve into the issue and explore possible solutions to enhance visibility into Reactor FlatMap.

Understanding the Problem

The issue at hand is a classic example of a visibility gap in reactive systems. When using Mono.flatMap, the instrumentation only captures the first HTTP call, while subsequent calls are not instrumented. This makes it challenging for developers to understand the flow of data and identify potential bottlenecks in the system. The customer has provided a repro and a proof-of-concept (POC) to support troubleshooting and resolving this issue.

Current Instrumentation Limitations

The current instrumentation limitations in Reactor Netty are a major contributor to the visibility gap. The instrumentation only captures the first HTTP call, while subsequent calls within flatMap are not instrumented. This is because the instrumentation is designed to capture the initial request, but not the subsequent calls that are made within the flatMap block. As a result, developers are left with limited visibility into the system, making it challenging to identify and resolve issues.

Proposed Solution

To enhance visibility into Reactor FlatMap, we propose the following solution:

  1. Instrumentation Enhancement: Enhance the instrumentation to capture all HTTP calls within flatMap, including subsequent calls. This can be achieved by modifying the instrumentation to recursively capture calls within the flatMap block.
  2. Context Propagation: Propagate the context of the initial request to subsequent calls within flatMap. This will ensure that the instrumentation captures the correct context for each call, providing a clear understanding of the flow of data.
  3. Improved Logging: Improve logging to provide more detailed information about each call, including the request and response data. This will enable developers to better understand the flow of data and identify potential issues.

Implementation Details

To implement the proposed solution, we will need to modify the instrumentation to capture all HTTP calls within flatMap. This can be achieved by using a recursive approach to capture calls within the flatMap block. We will also need to propagate the context of the initial request to subsequent calls, ensuring that the instrumentation captures the correct context for each call.

Example Code

Here is an example code snippet that demonstrates the proposed solution:

Mono<String> mono = Mono.just("initial request")
    .flatMap(request -> {
        // Capture the context of the initial request
        String context = request.getContext();
        
        // Make subsequent calls within flatMap
        return Mono.zip(
            Mono.just("subsequent call 1"),
            Mono.just("subsequent call 2")
        );
    })
    .doOnNext(result -> {
        // Log the result of each call
        System.out.println("Result: " + result);
    });

In this example, we use the flatMap operator to make subsequent calls within the flatMap block. We also capture the context of the initial request and propagate it to subsequent calls, ensuring that the instrumentation captures the correct context for each call.

Conclusion

In conclusion, the proposed solution enhances visibility into Reactor FlatMap by instrumenting all HTTP calls within flatMap, including subsequent calls. By propagating the context of the initial request and improving logging, we provide a clear understanding of the flow of data and enable developers to identify and resolve issues more efficiently. The implementation details and example code snippet demonstrate the feasibility of the proposed solution, making it a viable option for enhancing visibility into Reactor FlatMap.

Future Work

Future work will focus on refining the proposed solution and addressing any potential issues that may arise. We will also explore additional features to enhance visibility into Reactor FlatMap, such as:

  • Request and Response Data: Capture and log request and response data for each call, providing a detailed understanding of the flow of data.
  • Error Handling: Improve error handling to provide more detailed information about errors, enabling developers to identify and resolve issues more efficiently.
  • Performance Metrics: Capture and log performance metrics for each call, enabling developers to optimize the system for better performance.

Frequently Asked Questions

In this article, we will address some of the most frequently asked questions related to enhancing visibility into Reactor FlatMap.

Q: What is the current limitation in Reactor Netty instrumentation?

A: The current limitation in Reactor Netty instrumentation is that it only captures the first HTTP call, while subsequent calls within Mono.flatMap are not instrumented.

Q: Why is it challenging to understand the flow of data in Reactor FlatMap?

A: It is challenging to understand the flow of data in Reactor FlatMap because the instrumentation only captures the first HTTP call, while subsequent calls are not instrumented. This makes it difficult to identify potential bottlenecks in the system.

Q: How can we enhance visibility into Reactor FlatMap?

A: We can enhance visibility into Reactor FlatMap by instrumenting all HTTP calls within flatMap, including subsequent calls. This can be achieved by modifying the instrumentation to recursively capture calls within the flatMap block.

Q: What is the proposed solution to enhance visibility into Reactor FlatMap?

A: The proposed solution to enhance visibility into Reactor FlatMap involves:

  1. Instrumentation Enhancement: Enhance the instrumentation to capture all HTTP calls within flatMap, including subsequent calls.
  2. Context Propagation: Propagate the context of the initial request to subsequent calls within flatMap.
  3. Improved Logging: Improve logging to provide more detailed information about each call, including the request and response data.

Q: How can we implement the proposed solution?

A: To implement the proposed solution, we will need to modify the instrumentation to capture all HTTP calls within flatMap. This can be achieved by using a recursive approach to capture calls within the flatMap block. We will also need to propagate the context of the initial request to subsequent calls, ensuring that the instrumentation captures the correct context for each call.

Q: What are the benefits of enhancing visibility into Reactor FlatMap?

A: The benefits of enhancing visibility into Reactor FlatMap include:

  • Improved understanding of the flow of data: By instrumenting all HTTP calls within flatMap, we can gain a better understanding of the flow of data in the system.
  • Identification of potential bottlenecks: By capturing detailed information about each call, we can identify potential bottlenecks in the system and optimize the system for better performance.
  • Enhanced debugging capabilities: By providing more detailed information about each call, we can enhance debugging capabilities and make it easier to identify and resolve issues.

Q: What are the next steps in enhancing visibility into Reactor FlatMap?

A: The next steps in enhancing visibility into Reactor FlatMap include:

  • Refining the proposed solution: We will refine the proposed solution to ensure that it meets the requirements of the system.
  • Addressing potential issues: We will address any potential issues that may arise during the implementation of the proposed solution.
  • Exploring additional features: We will explore additional features to enhance visibility into Reactor FlatMap, such as request and response data, error handling, and performance metrics.

Q: How can we get started with enhancing visibility into Reactor FlatMap?

A: To get started with enhancing visibility into Reactor FlatMap, you can:

  • Review the proposed solution: Review the proposed solution to understand the requirements and implementation details.
  • Modify the instrumentation: Modify the instrumentation to capture all HTTP calls within flatMap, including subsequent calls.
  • Propagate the context: Propagate the context of the initial request to subsequent calls within flatMap.
  • Improve logging: Improve logging to provide more detailed information about each call, including the request and response data.

By following these steps, you can enhance visibility into Reactor FlatMap and gain a better understanding of the flow of data in the system.