Netflix Feign - Propagate Status and Exception through Microservices

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());

Since 2017 we've created a library that does this from annotations (making it fairly easy to, just like for requests/etc, to code this up by annotations).

it basically allows you to code error handling as follows:

@ErrorHandling(codeSpecific =
    {
        @ErrorCodes( codes = {401}, generate = UnAuthorizedException.class),
        @ErrorCodes( codes = {403}, generate = ForbiddenException.class),
        @ErrorCodes( codes = {404}, generate = UnknownItemException.class),
    },
    defaultException = ClassLevelDefaultException.class
)
interface GitHub {

    @ErrorHandling(codeSpecific =
        {
            @ErrorCodes( codes = {404}, generate = NonExistentRepoException.class),
            @ErrorCodes( codes = {502, 503, 504}, generate = RetryAfterCertainTimeException.class),
        },
        defaultException = FailedToGetContributorsException.class
    )
    @RequestLine("GET /repos/{owner}/{repo}/contributors")
    List<Contributor> contributors(@Param("owner") String owner, @Param("repo") String repo);
}

You can find it in the OpenFeign organisation: https://github.com/OpenFeign/feign-annotation-error-decoder

disclaimer: I'm a contributor to feign and the main dev for that error decoder.

What we do is as follows:

Share common jar which contains exceptions with both microservices.

1.) In microservices A convert exception to a DTO class lets say ErrorInfo. Which will contain all the attributes of your custom exception with a String exceptionType, which will contain exception class name.

2.) When it is received at microservice B it will be handled by ErrorDecoder in microservice B and It will try to create an exception object from exceptionType as below:

@Override
public Exception decode(String methodKey, Response response) {       

ErrorInfo errorInfo = objectMapper.readValue(details, ErrorInfo.class);
Class exceptionClass;

Exception decodedException;

try {

    exceptionClass = Class.forName(errorInfo.getExceptionType());  

    decodedException = (Exception) exceptionClass.newInstance();

    return decodedException;

 }

 catch (ClassNotFoundException e) {

    return new PlatformExecutionException(details, errorInfo);

 }
  return defaultErrorDecoder.decode(methodKey, response);
 }

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

Write your custom exception mapper and register it. You can customize responses.

Complete example is here

public class GenericExceptionMapper implements ExceptionMapper<Throwable> {

    @Override
    public Response toResponse(Throwable ex) {
        return Response.status(500).entity(YOUR_RETURN_OBJ_HERE).build();
    }

}