Introduction

Notes from Spring Boot Microservices workshop by Java Brains

Application

Application consists of three microservices:

movie-catalog-service
movie-info-service
ratings-data-service
discovery-server

movie-catalog-service retrieves movie information from movie-info-service and movie ratings from ratings-data-service. Discovery-server is a microservice to locate each microservices on a network.

How to Run

Run each microservice as a standart Java application
Run catalog API: http://localhost:8081/catalog/foo
You can monitor Hystrix for Fault Tolerance: http://localhost:8081/hystrix/monitor?stream=http%3A%2F%2Flocalhost%3A8081%2Factuator%2Fhystrix.stream

Service Discovery

Why hardcoded URLs are bad?

Changes require code updates
Dynamic URLs in the cloud
Load balancing
Multiple environments

What is the minimum requirement for service discovery?

Discovery server

Client-side vs Server-side Discovery

Client-side Discovery

The client asks for a service to the discovery server
The discovery server returns the service
Client makes the call to the service

https://microservices.io/patterns/client-side-discovery.html

Server-side Discovery

The client makes a request to a service via a discovery server
The discovery server queries the service registry and routes each request to an available service instance

https://microservices.io/patterns/server-side-discovery.html

Eureka Service Discovery

If your Java version is 11, you will get JAXB errors as JAXB removed from JDK from Java 10 onwards.

java.lang.TypeNotPresentException: Type javax.xml.bind.JAXBContext not present at java.base/sun.reflect.generics.factory.CoreReflectionFactory.makeNamedType(CoreReflectionFactory.java:117) ~[na:na] at java.base/sun.reflect.generics.visitor.Reifier.visitClassTypeSignature(Reifier.java:125) ~[na:na] at java.base/sun.reflect.generics.tree.ClassTypeSignature.accept(ClassTypeSignature.java:49) ~[na:na]

You need to add the following dependencies below

<dependency> <groupId>com.sun.xml.bind</groupId> <artifactId>jaxb-impl</artifactId> <version>2.3.0</version> </dependency> <dependency> <groupId>org.glassfish.jaxb</groupId> <artifactId>jaxb-runtime</artifactId> <version>2.3.0</version> </dependency> <dependency> <groupId>javax.activation</groupId> <artifactId>activation</artifactId> <version>1.1.1</version> </dependency>

Solutions for slow microservice

Timeout

If one of your microservices is slow, you can add a timeout to your rest template. however, it doesn't fully solve the issue.

@LoadBalanced
@Bean
public RestTemplate getRestTemplate() {
	HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory();
	clientHttpRequestFactory.setConnectTimeout(3000);
	return  new RestTemplate(clientHttpRequestFactory);
}

Circuit breaker pattern

You have applied the Microservice architecture. Services sometimes collaborate when handling requests. When one service synchronously invokes another there is always the possibility that the other service is unavailable or is exhibiting such high latency it is essentially unusable. Precious resources such as threads might be consumed in the caller while waiting for the other service to respond. This might lead to resource exhaustion, which would make the calling service unable to handle other requests. The failure of one service can potentially cascade to other services throughout the application [reference]

This pattern has the following benefits

Services handle the failure of the services that they invoke
Automatic recovery

This pattern has the following issues

It is challenging to choose timeout values without creating false positives or introducing excessive latency.

What to do when a circuit breaks?

Throw an error - not a good idea
Return a fallback "default" response - better than throwing an error but not an ideal option
Cache previous responses and use when possible - this would the best way to handle circuit breaks

What is Hystrix?

Netflix has created a library called Hystrix that implements the circuit breaker pattern.
A service failure in the lower level of services can cause cascading failure all the way up to the user. Having an open circuit stops cascading failures and allows overwhelmed or failing services time to recover. [reference]

Adding Hystrix to a Spring Boot app

Add spring-cloud-starter-netflix-hystrix pom dependency

  <dependency>
  	<groupId>org.springframework.cloud</groupId>
  	<artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
  </dependency>

Add @EnableCircuitBreaker to the application class
Add @HystrixCommand to the methods that need circuit breaker
Configure Hystrix behaviour

barrida/spring-boot-microservices-workshop