MicroService

What are microservices?
Microservices are a modern approach to software whereby application code is delivered in small, manageable pieces, independent of others.

Why build microservices?
Their small scale and relative isolation can lead to many additional benefits, such as easier maintenance, improved productivity, greater fault tolerance, better business alignment, and more.

Microservices with Spring Boot
With Spring Boot, your microservices can start small and iterate fast. That’s why it has become the de facto standard for Java™ microservices.

Microservice resilience with Spring Cloud
The distributed nature of microservices brings challenges. Spring helps you mitigate these. With several ready-to-run cloud patterns, Spring Cloud can help with service discovery, load-balancing, circuit-breaking, distributed tracing, and monitoring. It can even act as an API gateway.

Eureka is a REST (Representational State Transfer) based service that is primarily used in the AWS cloud for locating services for the purpose of load balancing and failover of middle-tier servers.
Eureka 是一个基于 REST 的服务，主要在 AWS 云中使用, 定位服务来进行中间层服务器的负载均衡和故障转移。

Zuul is the front door for all requests from devices and web sites to the backend of the Netflix streaming application. As an edge service application, Zuul is built to enable dynamic routing, monitoring, resiliency and security. It also has the ability to route requests to multiple Amazon Auto Scaling Groups as appropriate.


Spring Core
Annotation
@Resource:
Spring also supports injection by using the JSR-250 @Resource annotation (javax.annotation.Resource) on fields or bean property setter methods.
@Value: is typically used to inject externalized properties
@Component: is a generic stereotype for any Spring-managed component
@Repository: DAO / persistence layer
@Service: service layer
@Controller: MVC
@Named(JSR-330)/@ManagedBean(JSR-250): Similar to @Component.

@Autowired/@Inject: used at the field level, method level and constructor-argument level. Could even declare your injection point as a Provider, allowing for on-demand access to beans of shorter scopes or lazy access to other beans through a Provider.get() call.

@Configuration
Annotating a class with @Configuration indicates that its primary purpose is as a source of bean definitions.
@Configuration is meta-annotated with @Component.
@Bean
The @Bean annotation is used to indicate that a method instantiates, configures, and initializes a new object to be managed by the Spring IoC container.
Usually within @Configuration

Spring AOP usage:
Spring configuration & Spring transaction
Advice:
Each advice is a Spring bean. An advice instance can be shared across all advised objects or be unique to each advised object.
Advisor:
an Advisor is an aspect that contains only a single advice object associated with a pointcut expression.