Eureka 初识

官网：https://github.com/Netflix/eureka/wiki/Eureka-at-a-glance

只将官网的英文通过 翻译插件翻译，然后 记录在博客中，以便后续观看；

一、Eureka 是什么？

【官方英文】
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. 
We call this service, the Eureka Server. Eureka also comes with a Java-based client component,
the Eureka Client, which makes interactions with the service much easier. 
The client also has a built-in load balancer that does basic round-robin load balancing. 
At Netflix, a much more sophisticated load balancer wraps Eureka to provide weighted load balancing based on several factors like traffic, resource usage, 
error conditions etc to provide superior resiliency.

【插件翻译中文】
Eureka 是一种基于 REST（代表性状态传输）的服务，主要用于 AWS 云中，
用于定位服务，以实现中间层服务器的负载平衡和故障转移。
我们将此服务称为 Eureka Server。 Eureka 还附带了一个基于 Java 的客户端组件，
即 Eureka Client，它使与服务的交互变得更加容易。
客户端还有一个内置的负载均衡器，可以进行基本的循环负载均衡。
在 Netflix，一个更复杂的负载均衡器封装了 Eureka，以提供基于流量、资源使用、
错误条件等多个因素的加权负载均衡，以提供卓越的弹性。

　　

二、Eureka 用于什么？

【官方英文】
In AWS cloud, because of its inherent nature, servers come and go. 
Unlike the traditional load balancers which work with servers with well known IP addresses and host names, 
in AWS, load balancing requires much more sophistication in registering and 
de-registering servers with load balancer on the fly. 
Since AWS does not yet provide a middle tier load balancer, 
Eureka fills a big gap in the area of mid-tier load balancing.

【插件中文】
在 AWS 云中，由于其固有的性质，服务器来来去去。
与使用已知 IP 地址和主机名的服务器一起工作的传统负载均衡器不同，
在 AWS 中，负载均衡需要在使用负载均衡器动态注册和注销服务器时更加复杂。
由于 AWS 尚未提供中间层负载均衡器，
Eureka 填补了中间层负载均衡领域的一大空白。

　　

三、Netflix 如何使用 Eureka？

【官方英文】
At Netflix, Eureka is used for the following purposes apart from playing a critical part in mid-tier load balancing.
    1、For red/black deployments with Netflix Asgard- an open source service which makes cloud deployment easier. Eureka interacts with Asgard to make switching between older/newer release of a deployment of services quick and seamless in case of problems - especially given that launching 100's of instances to deploy a release could take a long time.
    2、For our cassandra deployments to take instances out of traffic for maintenance.
    3、For our memcached caching services to identify the list of nodes in the ring.
    4、Used for carrying other additional application specific metadata about services for various other reasons.

【插件中文】
在 Netflix，Eureka 除了在中间层负载平衡中发挥关键作用外，还用于以下目的：
    1、用于 Netflix Asgard 的红/黑部署 - 一种使云部署更容易的开源服务。 
Eureka 与 Asgard 交互，以便在出现问题时快速无缝地在服务部署的较旧/较新版本之间切换 - 
特别是考虑到启动 100 个实例来部署一个版本可能需要很长时间。
    2、让我们的 cassandra 部署从流量中取出实例以进行维护。
    3、让我们的 memcached 缓存服务识别环中的节点列表。
    4、出于各种其他原因，用于携带有关服务的其他附加应用程序特定元数据。

　　

四、我什么时候应该使用 Eureka？

【官方英文】
You typically run in the AWS cloud and you have a host of middle tier services 
which you do not want to register with AWS ELB or expose traffic from outside world. 
You are either looking for a simple round-robin load balancing solution or are willing to write your own wrapper around Eureka based on your load balancing need. 
You do not have the need for sticky sessions and load session data in an external cache such as memcached. 
More importantly, if your architecture fits the model where a client based load balancer is favored, Eureka is well positioned to fit that usage.

【插件中文】
您通常在 AWS 云中运行，并且您有许多中间层服务，
您不想向 AWS ELB 注册或暴露来自外部世界的流量。
您要么正在寻找一个简单的循环负载平衡解决方案，要么愿意根据您的负载平衡需求编写自己的 Eureka 包装器。您不需要粘性会话并将会话数据加载到外部缓存（如 memcached）中。
更重要的是，如果您的架构适合使用基于客户端的负载均衡器的模型，那么 Eureka 就可以很好地适应这种用法。

　　

五、应用程序客户端和应用程序服务器如何通信？

【官方英文】
The communication technology could be anything you like.
Eureka helps you find the information about the services 
you would want to communicate with but does not impose any restrictions on the protocol or method of communication. 
For instance, you can use Eureka to obtain the target server address and use protocols such as thrift, http(s) or any other RPC mechanisms.

【插件中文】
通信技术可以是你喜欢的任何东西。 
Eureka 帮助您找到有关您希望与之通信的服务的信息，
但不对通信协议或方法施加任何限制。
例如，您可以使用 Eureka 获取目标服务器地址并使用诸如 thrift、http(s) 或任何其他 RPC 机制之类的协议。