官方：https://spring.io/projects/spring-cloud-bus
Spring Cloud Bus links nodes of a distributed system with a lightweight message broker. This can then be used to broadcast state changes (e.g. configuration changes) or other management instructions. AMQP and Kafka broker implementations are included with the project. Alternatively, any Spring Cloud Stream binder found on the classpath will work out of the box as a transport. –摘自官网
官方：https://spring.io/projects/spring-cloud-config
简要描述：config(配置)又称为 统一配置中心顾名思义,就是将配置统一管理,配置统一管理的好处是在日后大规模集群部署服务应用时相同的服务配置一致,日后再修改配置只需要统一修改全部同步,不需要一个一个服务手动维护。
官方：https://spring.io/projects/spring-cloud-gateway
This project provides a library for building an API Gateway on top of Spring MVC. Spring Cloud Gateway aims to provide a simple, yet effective way to route to APIs and provide cross cutting concerns to them such as: security, monitoring/metrics, and resiliency.
官方：https://github.com/Netflix/zuul/wiki
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.
网关统一服务入口，可方便实现对平台众多服务接口进行管控，对访问服务的身份认证、防报文重放与防数据篡改、功能调用的业务鉴权、响应数据的脱敏、流量与并发控制，甚至基于API调用的计量或者计费等等。
网关 = 路由转发 + 过滤器
路由转发：接收一切外界请求，转发到后端的微服务上去；
过滤器:在服务网关中可以完成一系列的横切功能，例如权限校验、限流以及监控等，这些都可以通过过滤器完成。
In a distributed environment, inevitably some of the many service dependencies will fail. Hystrix is a library that helps you control the interactions between these distributed services by adding latency tolerance and fault tolerance logic. Hystrix does this by isolating points of access between the services, stopping cascading failures across them, and providing fallback options, all of which improve your system’s overall resiliency. –[摘自官方]
官方：https://cloud.spring.io/spring-cloud-openfeign/reference/html/
Feign是一个声明式的伪Http客户端，它使得写Http客户端变得更简单。使用Feign，只需要创建一个接口并注解。它具有可插拔的注解特性(可以使用springmvc的注解)，可使用Feign 注解和JAX-RS注解。Feign支持可插拔的编码器和解码器。Feign默认集成了Ribbon，默认实现了负载均衡的效果并且springcloud为feign添加了springmvc注解的支持。
在整个微服务架构中,我们比较关心的就是服务间的服务改如何调用,有哪些调用方式?
在springcloud中服务间调用方式主要是使用 http restful方式进行服务间调用
consul是一个可以提供服务发现，健康检查，多数据中心，Key/Value存储等功能的分布式服务框架，用于实现分布式系统的服务发现与配置。与其他分布式服务注册与发现的方案，使用起来也较为简单。Consul用Golang实现，因此具有天然可移植性(支持Linux、Windows和Mac OS X)；安装包仅包含一个可执行文件，方便部署。
