Spring-Boot & Netflix OSS - An adventure into microservices

Honestly, I still need convincing on microservices.

I can see that they are a compelling argument compared to a monolithic application, but I think I need to get my head around some of the challenges they face - the first one that comes to mind being how to effectively define the microservice boundaries - as it seems to me a lot of the applications I have ever worked with are monolithic because these boundaries are so blurred.


Anyway, I wanted to do some tech stuff, so decided to start building out an application using the microservice architectural pattern and Spring Boot seemed like a good place to get started.

This is very much a work in progress, and I am continuing to progress through different aspects of the application and at the moment there is very little actual code written (in part that is due to the simplicity that Spring-Boot provides).  All code is being kept up to date in GitHub so feel free to have a look at that.


There are lots of great blogs covering this stuff already, so won't re-cover their work, the following article gives a great write up of the Netflix OSS and the Spring integration which is worth reading:


(Image from: Building Microservices with Spring-Cloud and Netflix OSS)

Getting started: A service registry - Eureka

One of the first things that is needed is a central Service Registry to allow service-discovery - this is not a new concept to microservices and is an approach used by SOA.  Straight out of the box, Spring-Boot provides integration with Netflix's OSS application Eureka, that provides this.  I opted to have a dedicated application for my registry (code can be seen here) and it really is as simple as adding the relevant dependencies to the build.gradle file, adding an @EnableEurekaServer annotation to our application config then a simple config file defining the server port/name etc and its done!  You can just run gradle assemble in that project to build the JAR file, then run java -jar [the new JAR file] and the application will spin up - you should then be able to go to http://localhost:1111 and you will see the Eureka dashboard (with no microservices registered of course).

My first microservice

So, I had Eureka up and running, but it was looking pretty lonely with no services registered.

A microservice in Spring is also very simple - as really, all it is is a simple web application that runs in its own process with a limited domain - so spinning up a Spring Boot MVC RESTful webapp with a single controller/endpoint is enough to get me a microservice (even just a tweet would do it..)

@Controller class ThisWillActuallyRun { @RequestMapping("/") @ResponseBody String home() { "Hello World!" } }

— Rob Winch (@rob_winch) August 6, 2013

So we can create our new microservice to do anything we like, in my case I created a QuoteService (the application is slowly evolving into an insurance engine).  Just having the standalone app isn't helping much, so we need to add some configuration to tell the service to register with our Eureka server - this will make our new microservice discoverable by other services wanting to use it. 

Again this is quite simple: we need to tell our application it should try and register with Eureka, and we should add the config to do so:

You can see that we simply annotate our application config in java, and then add some properties that define where the Eureka server is hosted and that's basically it.

Now if we build the project JAR and start up again (and we still have our Eureka service registry running) then after 30seconds or so you should see the Quote-Service registered and ready to use.

On to the next one.. 

Now, we have a microservice, and we have a registry that makes it discoverable, but still - just one microservice is pretty lonely. So next I created another dummy RESTful microservice, this time called ProductService which just followed the same pattern as the first.

Once that was started up then the Eureka dashboard started looking a bit happier with the two services registered - the obvious next challenge is seamless interaction between the two: splitting the services into their own processes is all good an well, but meaningless if you can't easily integrate them.  The way I look at it is when reading the application code of a service (or application using microservices) then it should just look like a normal application with sevice classes - there shouldn't be any fanfare around the fact that my service class actually gets the data from a dedicated microservice over HTTP/AMQP rather than just getting directly from the DB in the traditional way.


So, still just stubbing out the endpoints, I updated my QuoteService endpoint to make a call to my ProductService, and then just jammed that response into the JSON response I was returning anyway:

As you can see, it could be a standard controller in a normal monolithic application from this point, we are just calling a method on our autowired ProductService class and returning that.


So the really interesting part is in the ProductService class - at the moment this isn't a really elegant, abstracted class yes, so there is still some boiler plate, but that will have the advantage of making it clear what is going on:

As you can see, it's just making a REST call to the Product microservice and returning the response cast as a Map - but the really nice part of this is that the service url is just the service name (in this case "PRODUCT-SERVICE", that is injected to the class)  and with the RestTemplate annotated with Spring-Cloud's @LoadBalanced that microservice will be looked up in Eureka (and load balanced if there is more than one PRODUCT-SERVICE running).

So our setup is starting to take shape now - we have two microservices, both registered with Eureka and able to interact with each other in a fairly clean, loosely coupled way.

Don't push me, 'cos I'm close to the edge..

As your microservices start to proliferate, you will get different levels of service granularity, and undoubtedly you won't just want to expose all your microservices as a public API.  One option would be to create a RESTful application and define nicely named endpoints you want to expose and then use the standard integration described above to integrate it.

Fortunately, there is an easier way - Netflix provides a library called Zuul that can be simply configured to map URL patterns to given defined service names (and again looks up in the Eureka service registry).  Much like Eureka, this is super easy to setup and just needs an annotation and the config again:

And the config is pretty easy to understand:

As you can see, we just define service names against URL patterns.

Now once all are apps are up and running, and the microservices are registered on Eureka then you have a single API interface to start interacting with the services (rather than having to access each service on its designated port etc).

Conclusion

 So that's as far as I have got - I wired up the QuoteService to MongoDB so the data all gets persisted there (and have added a get quote endpoint which gets the same data from mongo) and starting to wire up the product service with JPA.  So far it's been enjoyable, and things are making more sense than when I started - but there are a few questions still:

• It seems like there is still duplication of service names throughout the different projects - for example the ProductService name ("product-service" - case insensitive) is proliferated throughtout - the service itself defines it, the QuoteService needs to know the name of the service, the Zuul edge server needs to know the name etc.  I guess this is unavoidable as these are intrinsic dependencies but still seems a bit flaky.
  
• It feels like the Service classes could be factored out - our ProductService class that allows HTTP REST interactions with the Product microservice would likely need to be re-used across all applications/microservices that need to use the Product microservice