Netflix Feign - Propagate Status and Exception through Microservices

Question

I'm using Netflix Feign to call to one operation of a Microservice A to other other operation of a Microservice B which validates a code using Spring Boot.

The operation of Microservice B throws an exception in case of the validation has been bad. Then I handled in the Microservices and return a HttpStatus.UNPROCESSABLE_ENTITY (422) like next:

@ExceptionHandler({
       ValidateException.class
    })
    @ResponseStatus(HttpStatus.UNPROCESSABLE_ENTITY)
    @ResponseBody
    public Object validationException(final HttpServletRequest request, final validateException exception) {
        log.error(exception.getMessage(), exception);
        error.setErrorMessage(exception.getMessage());
        error.setErrorCode(exception.getCode().toString());
        return error;
    }

So, when Microservice A calls to B in a interface as next:

@Headers("Content-Type: " + MediaType.APPLICATION_JSON_UTF8_VALUE)
@RequestLine("GET /other")
void otherOperation(@Param("other")  String other );

@Headers("Content-Type: " + MediaType.APPLICATION_JSON_UTF8_VALUE)
@RequestLine("GET /code/validate")
Boolean validate(@Param("prefix") String prefix);

static PromotionClient connect() {

    return Feign.builder()
        .encoder(new GsonEncoder())
        .decoder(new GsonDecoder())
        .target(PromotionClient.class, Urls.SERVICE_URL.toString());
}

and the validations fails it returns a internal error 500 with next message:

{
  "timestamp": "2016-08-05T09:17:49.939+0000",
  "status": 500,
  "error": "Internal Server Error",
  "exception": "feign.FeignException",
  "message": "status 422 reading Client#validate(String); content:\n{\r\n  \"errorCode\" : \"VALIDATION_EXISTS\",\r\n  \"errorMessage\" : \"Code already exists.\"\r\n}",
  "path": "/code/validate"
}

But I need to return the same as the Microservice operation B.

Which would be the best ways or techniques to propagate Status and Exceptions through microservices using Netflix Feign?

Answer 1

You could use a feign ErrorDecoder

https://github.com/OpenFeign/feign/wiki/Custom-error-handling

Here is an example

public class MyErrorDecoder implements ErrorDecoder {

    private final ErrorDecoder defaultErrorDecoder = new Default();

    @Override
    public Exception decode(String methodKey, Response response) {
        if (response.status() >= 400 && response.status() <= 499) {
            return new MyBadRequestException();
        }
        return defaultErrorDecoder.decode(methodKey, response);
    }

}

For spring to pick up the ErrorDecoder you have to put it on the ApplicationContext:

@Bean
public MyErrorDecoder myErrorDecoder() {
  return new MyErrorDecoder();
}

Answer 2

Shameless plug for a little library I did that uses reflection to dynamically rethrow checked exceptions (and unchecked if they are on the Feign interface) based on an error code returned in the body of the response.

More information on the readme : https://github.com/coveo/feign-error-decoder

Answer 3

OpenFeign's FeignException doesn't bind to a specific HTTP status (i.e. doesn't use Spring's @ResponseStatus annotation), which makes Spring default to 500 whenever faced with a FeignException. That's okay because a FeignException can have numerous causes that can't be related to a particular HTTP status.

However you can change the way that Spring handles FeignExceptions. Simply define an ExceptionHandler that handles the FeignException the way you need it (see here):

@RestControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(FeignException.class)
    public String handleFeignStatusException(FeignException e, HttpServletResponse response) {
        response.setStatus(e.status());
        return "feignError";
    }

}

This example makes Spring return the same HTTP status that you received from Microservice B. You can go further and also return the original response body:

response.getOutputStream().write(e.content());