How do you debug and monitor reactive systems with tools like ReactiveX or Project Reactor?

1 Debugging Reactive Systems

One of the main difficulties of debugging reactive systems is that the stack traces are often not very helpful, as they may not show the actual source of the error or the relevant context. To overcome this, you can use some tools and features that can enhance the stack traces and provide more information. For example, you can use the

onErrorMap        

operator to wrap the exceptions with custom messages or types, or the

doOnError        

operator to log the errors or perform some actions. You can also use the

checkpoint        

operator in Project Reactor to mark specific points in the stream and add them to the stack trace. Alternatively, you can use the

DebugSubscriber        

in ReactiveX to attach a debugger to the stream and inspect the values and events.

2 Monitoring Reactive Systems

Another challenge of monitoring reactive systems is that they are often distributed and dynamic, which makes it hard to measure and observe their performance and behavior. To address this, you can use some tools and frameworks that can collect and visualize metrics and logs from your reactive applications. For example, you can use the

Micrometer        

library to instrument your reactive streams and expose metrics such as throughput, latency, errors, and backpressure. You can also use the

Reactor-Netty        

module to monitor the network traffic and connections of your reactive web applications. Additionally, you can use the

Spring Boot Actuator        

framework to expose health indicators and endpoints for your reactive services. These tools can help you integrate your reactive applications with external systems such as Prometheus, Grafana, or ELK.

3 Testing Reactive Systems

Besides debugging and monitoring, testing is also an essential part of developing and maintaining reactive systems. Testing reactive systems can be tricky, as they may involve asynchronous and non-deterministic behavior, time dependencies, and concurrency issues. To cope with this, you can use some tools and libraries that can simplify and automate the testing process. For example, you can use the

TestObserver        

and

TestSubscriber        

classes in ReactiveX and Project Reactor, respectively, to assert and verify the values and events emitted by the streams. You can also use the

TestScheduler        

class to control and manipulate the time and scheduler used by the streams. Furthermore, you can use the

StepVerifier        

class in Project Reactor to create fluent and expressive tests for your reactive streams.

4 Debugging Tips and Tricks

In addition to using the tools and techniques mentioned above, there are some general tips and tricks that can help you debug your reactive systems more effectively. For instance, you can use the

doOnNext        

,

doOnComplete        

, and

doOnCancel        

operators to log or print the values and events that occur in the stream. You can also use the

materialize        

and

dematerialize        

operators to convert the stream into a stream of notifications that contain the values, errors, and completions. This can help you inspect the stream more easily and handle the errors more gracefully. Moreover, you can use the

timeout        

,

retry        

, and

retryWhen        

operators to deal with slow or failing streams and avoid blocking or hanging your application.

5 Monitoring Best Practices

Similarly, there are some best practices that can help you monitor your reactive systems more efficiently and reliably. For example, you can use the

name        

and

tags        

methods in Project Reactor to assign meaningful names and tags to your streams, which can help you identify and group them in your metrics and logs. You can also use the

@Timed        

and

@Counted        

annotations in Micrometer to easily measure the duration and count of your methods and streams. Additionally, you can use the

@EnableWebFluxSecurity        

annotation in Spring Boot to enable security features and filters for your reactive web applications. These best practices can help you improve the quality and security of your reactive systems.

6 Testing Patterns and Anti-Patterns

Finally, there are some patterns and anti-patterns that you should be aware of when testing your reactive systems. Some of the patterns include using the

subscribeWith        

method to reuse your test subscribers, using the

assertNoErrors        

and

assertComplete        

methods to check for errors and completion, and using the

withVirtualTime        

method to test time-dependent streams. Some of the anti-patterns include using blocking methods such as

block        

,

toIterable        

, or

get        

, using thread sleep or countdown latches to wait for asynchronous events, and using mutable state or shared resources in your tests. These patterns and anti-patterns can help you write more robust and reliable tests for your reactive systems.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?