Tech-Notes

Spring Cloud

Spring cloud annoatations

1. @EnableConfigServer
2. @EnableEurekaServer
3. @EnableDiscoveryClient
4. @EnableCircuitBreaker
5. @HystrixCommand

Config server

1. starter pack = spring-cloud-config-server
2. Add @EnableConfigServer along with @SpringBootApplication
3. Add Application.properties.
   a. server.port=8081
   b. spring.cloud.config.server.git.uri=github.com, or spring.cloud.config.server.native.searchLocations
4. Now Can check actuator Url: localhost:8888/application/default will print property source uri and details

How to use it

1. Add @RefreshScope along with @SpringBootApplication
2. Add Application.properties
   a) spring.application.name = config-client
   b) spring.cloud.config.uri = http://localhost:8888
   Note: we can refresh the cache using actuator

Service Discovery

1. starter pack = Eureka server starter
2. Add @EnableEurekaServer along with @SpringBootApplication
3. Add Application.properties
   a) server.port=8761
   b) eureka.client.register-with-eureka=false
   c) eureka.client.fetch-registry=false f

How to use it

1. Add dependency spring-cloud-netflix-eureka-client in pom.xml
   -then it automatically register with service registry 8761
2. Add @LoadBalanced along with @Autowired RestTemplate restTemplate; -Loadbalance happen at client side
3. use restTemplate.getForObject(“http://", String.class); -no need to hardcode url, instead use app name

API Gateway - Routing

1. Starter pack - spring-cloud-zuul, spring-discovery-client, spring-web, actuator
2. Add Application.properties

   eureka.instance.preferIpAddress=true
   eureka.client.registerWithEureka=true
   eureka.client.fetchRegistry=true
   eureka.client.serviceUrl.defaultZone=http://localhost:8761/eureka  
   managment.endpoints.web.exposure.include= info,health,routes  
   spring.application.name=zuul-gateway  
   

3. Add @EnableZuulProxy, @EnableDiscoveryClient alons with @SpringBootApplication

Circuite Breaker

call RestTemplate via circuit breaker

@Autowired
private RestTemplate restTemplate;
@Autowired
private CircuitBreakerFactory circuiteBreakerFactory;

public String getService(){
  CircuitBreaker cb = circuiteBreakerFactory.create("nameserivcebreaker");
  return cb.run(() -> restTemplate.getForObject("http://localhost:8082", String.class), throwable -> return "fallback");
}
@Bean  
public RestTemplate restTemplate(){
  return new RestTemplate();
}

BulkHead - handling maximum concurrent calls

Rate limiter - amount request handling

Retry - number of times retry