MicroProfile

This example walks you through how to use MicroProfile Fault Tolerance in the Helidon Project.

Fault Tolerance MicroProfile feature

MicroProfile brings to Java/Jakarta EE ecosystem resilient features as Circuit Breakers, Timeout, Fallback and Retry.

Example

Running the application

mvn clean package && java -jar target/helidon-microprofile.jar

How does it work?

When statusOfDayByAccuWeather is invoked, it calls longRunningTask that hangs for 80ms which causes the interruption of statusOfDayByAccuWeather due to the threshold of @Timeout annotation that is set up for 50ms only. When the interruption happens, an exception is thrown and it actives the Retry Policy which detects that an error happened and repeat the same operation accordingly to the value defined by maxRetries.

As longRunningTask is meant to fail by our timeout criteria, @Fallback annotation take place with a fallback method to ensure that the operation has another chance to concluded successfully.

@ApplicationScoped
public class WeatherGateway {
..

    @Timeout(50)
    @Retry(maxRetries = 3)
    @Fallback(fallbackMethod = "statusOfWeekByMetEireann")
    @CircuitBreaker(requestVolumeThreshold=2, failureRatio=0.5, successThreshold=2)
    public String statusOfDayByAccuWeather(){
        return longRunningTask();
    }
..
    public String statusOfWeekByMetEireann(){
        LOGGER.log(Level.WARNING, "MetEireann backup service has been requested due to AccuWeather timeout");
        return "A beautiful day";
    }
..
    private String longRunningTask(){
        try {
            Thread.sleep(80);
        } catch (InterruptedException e) {
            LOGGER.log(Level.WARNING,"AccuWeather task has been interrupted.");
        }
        return null;
    }
}

Day status call

GET http://localhost:8080/weather/statusOfDay

Server log

INFO ...CommandRetrier : About to execute command with key statusOfDayByAccuWeather361059497
INFO ...FaultToleranceCommand : Enter: breaker for statusOfDayByAccuWeather361059497 in state CLOSED_MP

> WARNING io.jventura.weather.WeatherGateway : AccuWeather task has been interrupted.

INFO ...CommandRetrier : About to execute command with key statusOfDayByAccuWeather361059497
INFO ...FaultToleranceCommand : Enter: breaker for statusOfDayByAccuWeather361059497 in state CLOSED_MP

> WARNING io.jventura.weather.WeatherGateway : AccuWeather task has been interrupted.

INFO ...CommandRetrier : About to execute command with key statusOfDayByAccuWeather361059497
INFO ...FaultToleranceCommand : Enter: breaker for statusOfDayByAccuWeather361059497 in state CLOSED_MP

> WARNING io.jventura.weather.WeatherGateway : AccuWeather task has been interrupted.

INFO ...CircuitBreakerHelper : Circuit breaker for statusOfDayByAccuWeather361059497 now in state OPEN_MP
INFO ...FaultToleranceCommand : Attempting to trip circuit breaker for command statusOfDayByAccuWeather361059497
INFO ...FaultToleranceCommand : Attempt to manually open breaker failed for command statusOfDayByAccuWeather36105949

INFO ...CommandRetrier : About to execute command with key statusOfDayByAccuWeather361059497
INFO ...FaultToleranceCommand : Enter: breaker for statusOfDayByAccuWeather361059497 in state OPEN_MP

> WARNING io.jventura.weather.WeatherGateway : MetEireann backup service has been requested due to AccuWeather timeout

Response

A beautiful day!

Running the test

You can also try it out using the WeatherTest.java available in the project.

mvn clean test