Get failure exception in @HystrixCommand fallback method

Question

Is there a way to get the reason a HystrixCommand failed when using the @HystrixCommand annotation within a Spring Boot application? It looks like if you implement your own HystrixCommand, you have access to the getFailedExecutionException but how can you get access to this when using the annotation? I would like to be able to do different things in the fallback method based on the type of exception that occurred. Is this possible?

I saw a note about HystrixRequestContext.initializeContext() but the HystrixRequestContext doesn't give you access to anything, is there a different way to use that context to get access to the exceptions?

score 53 · Answer 1 · answered Mar 07 '16 at 02:04

Simply add a Throwable parameter to the fallback method and it will receive the exception which the original command produced.

From https://github.com/Netflix/Hystrix/tree/master/hystrix-contrib/hystrix-javanica

    @HystrixCommand(fallbackMethod = "fallback1")
    User getUserById(String id) {
        throw new RuntimeException("getUserById command failed");
    }

    @HystrixCommand(fallbackMethod = "fallback2")
    User fallback1(String id, Throwable e) {
        assert "getUserById command failed".equals(e.getMessage());
        throw new RuntimeException("fallback1 failed");
    }

For `Throwable e`, it can show me the real reason, like FAILURE/SHORTCIRCUITED/TIMEOUT/BAD_REQUEST/SEMAPHORE_REJECTED/THREAD_POOL_REJECTED. Someone said they could not, since they need to tweak javanica to use getExecutionException() instead of getFailedExecutionException() as @vicco mentioned. — Anderson, May 12 '20 at 09:19

score 20 · Accepted Answer · answered Sep 29 '15 at 16:15

I haven't found a way to get the exception with Annotations either, but creating my own Command worked for me like so:

public static class DemoCommand extends HystrixCommand<String> {

    protected DemoCommand() {
        super(HystrixCommandGroupKey.Factory.asKey("Demo"));
    }

    @Override
    protected String run() throws Exception {
        throw new RuntimeException("failed!");
    }

    @Override
    protected String getFallback() {
        System.out.println("Events (so far) in Fallback: " + getExecutionEvents());
        return getFailedExecutionException().getMessage();
    }

}

Hopefully this helps someone else as well.

vicco · Answer 3 · 2018-06-20T03:15:14.897

As said in the documentation Hystrix-documentation getFallback() method will be thrown when:

Whenever a command execution fails: when an exception is thrown by construct() or run()
When the command is short-circuited because the circuit is open
When the command’s thread pool and queue or semaphore are at capacity
When the command has exceeded its timeout length.

So you can easily get what raised your fallback method called by assigning the the execution exception to a Throwable object.

Assuming your HystrixCommand returns a String

public class ExampleTask extends HystrixCommand<String> {
   //Your class body
}

do as follows:

@Override
    protected ErrorCodes getFallback() {
        Throwable t = getExecutionException();
        if (circuitBreaker.isOpen()) {
            // Log or something
        } else if (t instanceof RejectedExecutionException) {
            // Log and get the threadpool name, could be useful
        } else {
            // Maybe something else happened
        }
        return "A default String"; // Avoid using any HTTP request or ypu will need to wrap it also in HystrixCommand
    }

More info here

score 3 · Answer 4 · answered Sep 29 '15 at 12:29

3

I couldn't find a way to obtain the exception with the annotations, but i found HystrixPlugins , with that you can register a HystrixCommandExecutionHook and you can get the exact exception in that like this :

HystrixPlugins.getInstance().registerCommandExecutionHook(new HystrixCommandExecutionHook() {
            @Override
            public <T> void onFallbackStart(final HystrixInvokable<T> commandInstance) {

            }
        });

The command instance is a GenericCommand.

answered Sep 29 '15 at 12:29

Ákos Ratku

1,421
12
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But that will generically catch them on every execution of a command and won't be tied to the specific command execution correct? Not quite what I was after, but still could be helpful in some cases where you need to know about failures. – Andrew Serff Sep 29 '15 at 16:09

score 3 · Answer 5 · answered Dec 01 '16 at 14:51

Most of the time just using getFailedExecutionException().getMessage() gave me null values.

   Exception errorFromThrowable = getExceptionFromThrowable(getExecutionException());
   String errMessage = (errorFromThrowable != null) ? errorFromThrowable.getMessage()

this gives me better results all the time.

Get failure exception in @HystrixCommand fallback method

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