Sunday, August 18, 2019

Declarative REST Client: Feign

We already know that how microservices communicate with each other using RestTemplate. In this blog, we will see that how this can happen using Feign Client as well. 

What is a Feign Client?

Feign is an abstraction over REST based call. It makes writing web service clients easier. It Is as easy as creating interface and then annotate it. It has pluggable annotation support including Feign annotations and JAX-RS annotations. It also supports pluggable encoders and decoders and has supports for Spring MVC annotation.

Using Feign, microservices can easily communicate with each other and developers don't have to bother about REST internal details and can only concentrate on business logic.

I am going to use my previous applications to demonstrate the working of Feign Client. So before starting feign-client application. Make sure all the below three applications are already up and running. 

Feign Client Implementation

  • Create a spring boot application and add Feign starter dependency to our pom.xml file.

  • Add @EnableFeignClients annotation. With this annotation, we enable component scanning for interfaces that declare they are Feign clients. 

  • Declare a Feign client using the @FeignClient annotation.

  • Either name or url must be passed under @FeignClient annotation. If name attribute present then it will fetch the service location from service registry and then hit product-service and in case of url, it will directly hit the application to get the data from product-service. In case of both present then it will always first check for the name attribute. 
  • Use Spring Web annotations to declare the APIs that we want to reach out to.
Note: If your application is not registered with service registry then directly use url attribute to get the data but I would recommend to use name attribute and to use name attribute, make sure your application is connecting to Eureka server to get the service location. 

Read my blog to understand on how to add support for Eureka Client to your application.

Now start your application and you should be able to fetch product-service from feign-client. 

You can download the source code from here. 

Custom Configuration

Feign Client also support for Custom configuration changes like telling Feign to use OkHttpClient instead of the default one in order to support HTTP/2. 

Let’s go deep down to check how can we customize Feign Client.

There are two ways to configure it i.e. using properties file or override them using a @Configuration class, which we then need to add to the FeignClient annotation. 

Properties file:

Using @Configuration


By default, a logger gets created for each Feign Client and to enable it, we have to declare it in the file using the package name of the client interface.

There are four logging levels to choose from:

NONE – no logging, which is the default
BASIC – log only the request method, URL, and response status
HEADERS – log the basic information together with request and response headers
FULL – log the body, headers, and metadata for both request and response

Handling Errors with Feign

By default, Feign’s default error handler, ErrorDecoder.default, always throws a FeignException.

To customize the Exception thrown, we can override it by writing our own Custom Error class and implements ErrorDecoder and declare this bean under @Configuration as we did earlier.

Spring-boot microservices can be downloaded from GITHUB

Happy Coding...!!!

Microservices: Service Registry and Discovery

In my previous blog, I have already talked about Netflix Hystrix Circuit Breaker Microservices and explained it by creating two applications i.e. Product Service and Price Service.
In this post, I’ll use both applications to explain what is the Service Registry and Discovery Server.

What is Service Registry and Discovery and why do we need it in the first place?

In our monolithic application, mostly service invoke one another through language methods or procedure calls and even in traditional distributed system deployment, services run at fixed, well-known locations (hosts and ports) and so can easily call one another using HTTP/REST. Over here the network locations of service instances are relatively static.

With the microservice architecture system, this is a much more difficult problem as service instances have dynamically assigned network locations. Service instances change dynamically because of auto-scaling, failure or upgrade. So, you can see that it’s not possible to hard code the locations (hosts and ports) of service instances in our application.

Apart from that, most of the time we have to deploy the same instance on multiple hosts (E.g. During Big billions day sale where 1000’s of instances is running to support high demand) which will be again a tedious task for the load balancer to register and deregister itself for all these services.

What is Service Registry and Discovery?

Service Registry is the server instance where all the service provider register itself when it starts up and deregisters itself when it leaves the system. The service instance’s registration is typically refreshed periodically using a heartbeat mechanism.

Whenever a client has to communicate with other service instances, it has to first query to Service registry to get the network location and then uses a load-balancing algorithm to select one of the available service instances and invoke a request. 

The above instance discovery pattern is called a Client-Side discovery pattern and this can be easily implemented using Netflix Eureka as a Service Registry. It provides a REST API for managing service‑instance registration and for querying available instances.

Netflix also provides Netflix Ribbon which is an IPC client that works with Eureka to load balance requests across the available service instances.


As we already have two microservices product-service and price-service and we know product-service is internally invoking price-service to get the price detail of the products. We will do minor changes with these two applications to support service registry.

Discovery Server Implementation

  • Create a spring boot application and Eureka Server starter dependency to your pom.xml file 

  • Add @EnableEurekaServer annotation to Enable Eureka Server.
  • By default, Each Eureka Server is also a Eureka Client which needs at least one service URL to locate service registry. We have to disable this feature as we are creating single node Eureka Server. 
  • Add below properties to file.

  • Now start the discovery-server application and access http://localhost:8761 which will display the UI similar to below screenshot. 

  • As of now, no application is registered with the Eureka Server. 

2. Registering product-service and price-service to Eureka Clients

  • Let’s make out product-service and price-service as Eureka Client which should register to Eureka Server itself on starts up.
  • Add Eureka Client dependency on both pom.xml files.

  • Configure eureka.client.service-url.defaultZone property in to automatically register with the Eureka Server. 

  • Now start product-service and price service application and hit http://localhost:8761. We will see product-service and price-service is registered with SERVICE ID as PRODUCT-SERVICE and PRICE-SERVICE respectively. We can also notice the status as UP(1) which means the services are up and running and only one instance of product and price-service are running. 

3. Update hard code URL with application name in product-service and restart the application. 

4. Now open browser and hit product URL and you will get the below response.

Congratulation!!! Our application is perfectly working with Discovery Service. 

Spring-boot microservices can be downloaded from GITHUB

Happy Coding...!!!

Sunday, June 16, 2019

Netflix Hystrix Circuit Breaker

Netflix Hystrix Circuit Breaker

In one of my previous blogs, I have already discussed the Circuit breaker pattern and its usage, Today, we will see how can we implement it in our application using Spring Cloud Netflix Hystrix.

In this document, I’ll walk you through the process of applying circuit breakers to potentially-failing method calls using the Netflix Hystrix fault tolerance library.

Hystrix is watching methods for failing calls to related services. If there is such a failure, it will open the circuit and forward the call to a fallback method.

To understand it in a better way, I’ll take the same problem statement that I have already discussed in my previous blog i.e. E-commerce Portal. 

I am assuming you must be aware of Spring boot framework as this implementation is completely based on it.

As per problem statement, we need two applications i.e. Product Service & Price Service but in this tutorial, I’ll talk about just Product Service as Price Service is simple web application exposing a single API and you can clone it from GitHub.

I’ll talk about Product Service in which we will integrate Circuit breaker pattern and Cache Service implementation and internally, it will invoke Price Service to get the Price Detail.

Optional: You can download the below project from GitHub or you can try it by creating a new one. I would recommend you to try it from scratch.

Product Service:

Create Spring boot application and add below dependency to your pom.xml file.

<!-- Optional. Application health monitor check -->





<!-- Compulsory for circuit breaker implementation -->





<!-- Optional. Dashboard in case you want to see the circuit state UI -->





To enable Circuit Breaker in spring boot application, add @EnableCircuitBreaker annotation on product-service entry-point class. 

Now use @HystrixCommand annotation on themethod we want to apply timeout and fallback method.

I have annotated @HystrixCommand(fallbackMethod = “getProductDetailFromCache”) on getProduct(String Id) so that if it doesn’t receive the response within the certain time limit or request get failed while calling price service API then fallback() should get called over here and fetch the price value from Cache Service. 

Make sure, the fallback method should be defined in the same class and should have the same signature.

We can customize the @HystrixCommand default behavior by configuring properties using @HystrixProperty annotations. Will check in depth in another blog. 

Add RestController class and other required class as per source code present in GitHub.

Add server.port to the file.

Start both applications and try to fetch the product Detail. In our case, our product-service app URL is:


Now try to fetch product which does not exist

You will observe that over here circuit breaker is still in the closed state even after the exception. 

Why? The reason is that we have added  ignoreExceptions = { ProductNotFoundException.class } to @HystrixCommand so that it should not trip circuit if the product is not present.

Now, Stop the price-service application and hit the product URL again:

Check the log:

Congratulations! Our application is working as expected.

Monitoring Circuit Breakers using Hystrix Dashboard

Hystrix comes with a decent dashboard where we can monitor the status of Hystrix commands

To enable it, Add Hystrix dashboard dependency to the pom.xml file 

<!-- Optional. Application health monitor check -->
<!-- Optional. Dashboard in case you want to see the circuit state UI -->

Add @EnableHystrixDashboard annotation on the entry point class

Add to file.

Start the product-service application and then go to http://localhost:port/hystrix to view the dashboard. 

In Hystrix Dashboard home page enter http://localhost:7001/actuator/ as stream URL and give Product Service as Title and click on Monitor Stream button. 

Now, we can see that the Circuit status along with how many calls succeed and how many failures occurred, etc. 

Spring-boot microservices can be downloaded from GITHUB

Happy Coding...!!!