Wednesday, June 22, 2016

Spring Cloud Zuul Support - Configuring Timeouts

Spring Cloud provides support for Netflix Zuul - a toolkit for creating edge services with routing and filtering capabilities.

Zuul Proxy support is very comprehensively documented at the Spring Cloud site. My objective here is to focus on a small set of attributes relating to handling timeouts when dealing with the proxied services.

Target Service and Gateway


To study timeouts better I have created a sample service(code available here) which takes in a configurable "delay" parameter as part of the request body and a sample request/response looks something like this:

A sample request with a 5 second delay:

{
  "id": "1",
  "payload": "Hello",
  "delay_by": 5000,
  "throw_exception": false
}


and an expected response:

{
  "id": "1",
  "received": "Hello",
  "payload": "Hello!"
}


This service is registered with an id of "sample-svc" in Eureka, a Spring Cloud Zuul proxy on top of this service has the following configuration:

zuul:
  ignoredServices: '*'
  routes:
    samplesvc:
      path: /samplesvc/**
      stripPrefix: true
      serviceId: sample-svc

Essentially forward all requests to /samplesvc/ uri to a service disambiguated with the name "sample-svc" via Eureka.

I also have a UI on top of the gateway to make testing with different delay's easier:


Service Delay Tests


The Gateway behaves without any timeout related issues when a low "delay" parameter is added to the service call, however if the delay parameter is changed as low as say 1 to 1.5 seconds the gateway would time out.

The reason is that if the Gateway is set up to use Eureka, then the Gateway uses Netflix Ribbon component to make the actual call. Further, the ribbon call is wrapped within Hystrix to ensure that the call remains fault tolerant. The first timeout that we are hitting is because Hystrix has a very low delay tolerance threshold and tweaking the hystrix settings should get us past the first timeout.

hystrix:
  command:
    sample-svc:
      execution:
        isolation:
          thread:
            timeoutInMilliseconds: 15000

Note that the Hystrix "Command Key" used for configuration is the name of the service as registered in Eureka.

This may be a little too fine grained for this specific Zuul call, if you are okay about tweaking it across the board then configuration along these lines should do the job:

hystrix:
  command:
    default:
      execution:
        isolation:
          thread:
            timeoutInMilliseconds: 15000

With this change the request to the service via the gateway with a delay of upto 5 seconds will now go through without any issues. If we were to go above 5 seconds though we would get another timeout. We are now hitting Ribbons timeout setting which again can be configured in a fine grained way for the specific service call by tweaking configuration which looks like this:

sample-svc:
  ribbon:
    ReadTimeout: 15000


With both these timeout tweaks in place the gateway based call should now go through

Conclusion


The purpose was not to show ways of setting arbitrarily high timeout values but just to show how to set values that may be more appropriate for your applications. Sensible timeouts are very important to ensure that bad service behaviors don't cascade upto the users. One thing to note is that if the gateway is configured without Ribbon and Eureka by specifying a direct url to a service then these timeout settings are not relevant at all.

If you are interested in exploring this further, the samples are available here.

Tuesday, June 7, 2016

Spring-Reactive samples

Spring-Reactive aims to bring reactive programming support to Spring based projects and this is expected to be available for the timelines of Spring 5. My intention here is to exercise some of the very basic signatures for REST endpoints with this model.

Before I go ahead let me acknowledge that this entire sample is completely based on the samples which S├ębastien Deleuze has put together here - https://github.com/sdeleuze/spring-reactive-playground

I wanted to consider three examples, first a case where existing Java 8 CompletableFuture is returned as a type, second where RxJava's Observable is returned as a type and third with Spring Reactor Core's Flux type.

Expected Protocol

The structure of the request and response message handled by each of the three service is along these lines, all of them will take in a request which looks like this:

{
 "id":1,
  "delay_by": 2000,
  "payload": "Hello",
  "throw_exception": false
}


The delay_by will make the response to be delayed and throw_exception will make the response to error out. A sane response will be the following:

{
  "id": "1",
  "received": "Hello",
  "payload": "Response Message"
}

I will be ignoring the exceptions for this post.

CompletableFuture as a return type


Consider a service which returns a java 8 CompletableFuture as a return type:

public CompletableFuture<MessageAcknowledgement> handleMessage(Message message) {
 return CompletableFuture.supplyAsync(() -> {
  Util.delay(message.getDelayBy());
  return new MessageAcknowledgement(message.getId(), message.getPayload(), "data from CompletableFutureService");
 }, futureExecutor);
}

The method signature of a Controller which calls this service looks like this now:

@RestController
public class CompletableFutureController {

 private final CompletableFutureService aService;

 @Autowired
 public CompletableFutureController(CompletableFutureService aService) {
  this.aService = aService;
 }

 @RequestMapping(path = "/handleMessageFuture", method = RequestMethod.POST)
 public CompletableFuture<MessageAcknowledgement> handleMessage(@RequestBody Message message) {
  return this.aService.handleMessage(message);
 }

}

When the CompletableFuture completes the framework will ensure that the response is marshalled back appropriately.

Rx Java Observable as a return type

Consider a service which returns a Rx Java Observable as a return type:

public Observable<MessageAcknowledgement> handleMessage(Message message) {
 logger.info("About to Acknowledge");
 return Observable.just(message)
   .delay(message.getDelayBy(), TimeUnit.MILLISECONDS)
   .flatMap(msg -> {
    if (msg.isThrowException()) {
     return Observable.error(new IllegalStateException("Throwing a deliberate exception!"));
    }
    return Observable.just(new MessageAcknowledgement(message.getId(), message.getPayload(), "From RxJavaService"));
   });
}

The controller invoking such a service can directly return the Observable as a type now and the framework will ensure that once all the items have been emitted the response is marshalled correctly.
@RestController
public class RxJavaController {

 private final RxJavaService aService;

 @Autowired
 public RxJavaController(RxJavaService aService) {
  this.aService = aService;
 }

 @RequestMapping(path = "/handleMessageRxJava", method = RequestMethod.POST)
 public Observable<MessageAcknowledgement> handleMessage(@RequestBody Message message) {
  System.out.println("Got Message..");
  return this.aService.handleMessage(message);
 }

}

Note that since Observable represents a stream of 0 to many items, this time around the response is a json array.


Spring Reactor Core Flux as a return type


Finally, if the response type is a Flux type, the framework ensures that the response is handled cleanly. The service is along these lines:

public Flux<messageacknowledgement> handleMessage(Message message) {
 return Flux.just(message)
   .delay(Duration.ofMillis(message.getDelayBy()))
   .map(msg -> Tuple.of(msg, msg.isThrowException()))
   .flatMap(tup -> {
    if (tup.getT2()) {
     return Flux.error(new IllegalStateException("Throwing a deliberate Exception!"));
    }
    Message msg = tup.getT1();
    return Flux.just(new MessageAcknowledgement(msg.getId(), msg.getPayload(), "Response from ReactorService"));
   });
}

and a controller making use of such a service:

@RestController
public class ReactorController {

 private final ReactorService aService;

 @Autowired
 public ReactorController(ReactorService aService) {
  this.aService = aService;
 }

 @RequestMapping(path = "/handleMessageReactor", method = RequestMethod.POST)
 public Flux<MessageAcknowledgement> handleMessage(@RequestBody Message message) {
  return this.aService.handleMessage(message);
 }

}

Conclusion

This is just a sampling of the kind of return types that the Spring Reactive project supports, the possible return types is way more than this - here is a far more comprehensive example.

I look forward to when the reactive programming model becomes available in the core Spring framework.

The samples presented in this blog post is available at my github repository