spring-cloud-netflix/2.0.x/multi/multi_spring-cloud-eureka-server.html

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   <title>2.&nbsp;Service Discovery: Eureka Server</title><link rel="stylesheet" type="text/css" href="css/manual-multipage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="multi_spring-cloud-netflix.html" title="Spring Cloud Netflix"><link rel="up" href="multi_spring-cloud-netflix.html" title="Spring Cloud Netflix"><link rel="prev" href="multi__service_discovery_eureka_clients.html" title="1.&nbsp;Service Discovery: Eureka Clients"><link rel="next" href="multi__circuit_breaker_hystrix_clients.html" title="3.&nbsp;Circuit Breaker: Hystrix Clients"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">2.&nbsp;Service Discovery: Eureka Server</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi__service_discovery_eureka_clients.html">Prev</a>&nbsp;</td><th width="60%" align="center">&nbsp;</th><td width="20%" align="right">&nbsp;<a accesskey="n" href="multi__circuit_breaker_hystrix_clients.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="spring-cloud-eureka-server" href="#spring-cloud-eureka-server"></a>2.&nbsp;Service Discovery: Eureka Server</h1></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="netflix-eureka-server-starter" href="#netflix-eureka-server-starter"></a>2.1&nbsp;How to Include Eureka Server</h2></div></div></div><p>To include Eureka Server in your project use the starter with group <code class="literal">org.springframework.cloud</code>
and artifact id <code class="literal">spring-cloud-starter-netflix-eureka-server</code>. See the <a class="link" href="https://projects.spring.io/spring-cloud/" target="_top">Spring Cloud Project page</a>
for details on setting up your build system with the current Spring Cloud Release Train.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="spring-cloud-running-eureka-server" href="#spring-cloud-running-eureka-server"></a>2.2&nbsp;How to Run a Eureka Server</h2></div></div></div><p>Example eureka server;</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@SpringBootApplication</span></em>
<em><span class="hl-annotation" style="color: gray">@EnableEurekaServer</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> Application {

    <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">static</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> main(String[] args) {
        <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> SpringApplicationBuilder(Application.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>).web(true).run(args);
    }

}</pre><p>The server has a home page with a UI, and HTTP API endpoints per the
normal Eureka functionality under <code class="literal">/eureka/*</code>.</p><p>Eureka background reading: see <a class="link" href="https://github.com/cfregly/fluxcapacitor/wiki/NetflixOSS-FAQ#eureka-service-discovery-load-balancer" target="_top">flux capacitor</a> and <a class="link" href="https://groups.google.com/forum/?fromgroups#!topic/eureka_netflix/g3p2r7gHnN0" target="_top">google group discussion</a>.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Tip"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="images/tip.png"></td><th align="left">Tip</th></tr><tr><td align="left" valign="top"><p>Due to Gradle&#8217;s dependency resolution rules and the lack of a parent bom feature, simply depending on spring-cloud-starter-netflix-eureka-server can cause failures on application startup. To remedy this the Spring Boot Gradle plugin must be added and the Spring cloud starter parent bom must be imported like so:</p><p><b>build.gradle.&nbsp;</b>
</p><pre class="programlisting">buildscript {
  dependencies {
    classpath(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"org.springframework.boot:spring-boot-gradle-plugin:1.3.5.RELEASE"</span>)
  }
}

apply plugin: <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"spring-boot"</span>

dependencyManagement {
  imports {
    mavenBom <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"org.springframework.cloud:spring-cloud-dependencies:Brixton.RELEASE"</span>
  }
}</pre><p>
</p></td></tr></table></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="spring-cloud-eureka-server-zones-and-regions" href="#spring-cloud-eureka-server-zones-and-regions"></a>2.3&nbsp;High Availability, Zones and Regions</h2></div></div></div><p>The Eureka server does not have a backend store, but the service
instances in the registry all have to send heartbeats to keep their
registrations up to date (so this can be done in memory). Clients also
have an in-memory cache of eureka registrations (so they don&#8217;t have to
go to the registry for every single request to a service).</p><p>By default every Eureka server is also a Eureka client and requires
(at least one) service URL to locate a peer. If you don&#8217;t provide it
the service will run and work, but it will shower your logs with a lot
of noise about not being able to register with the peer.</p><p>See also <a class="link" href="multi_spring-cloud-ribbon.html" title="6.&nbsp;Client Side Load Balancer: Ribbon">below for details of Ribbon
support</a> on the client side for Zones and Regions.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_standalone_mode" href="#_standalone_mode"></a>2.4&nbsp;Standalone Mode</h2></div></div></div><p>The combination of the two caches (client and server) and the
heartbeats make a standalone Eureka server fairly resilient to
failure, as long as there is some sort of monitor or elastic runtime
keeping it alive (e.g. Cloud Foundry). In standalone mode, you might
prefer to switch off the client side behaviour, so it doesn&#8217;t keep
trying and failing to reach its peers. Example:</p><p><b>application.yml (Standalone Eureka Server).&nbsp;</b>
</p><pre class="screen">server:
  port: 8761

eureka:
  instance:
    hostname: localhost
  client:
    registerWithEureka: false
    fetchRegistry: false
    serviceUrl:
      defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/</pre><p>
</p><p>Notice that the <code class="literal">serviceUrl</code> is pointing to the same host as the local
instance.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_peer_awareness" href="#_peer_awareness"></a>2.5&nbsp;Peer Awareness</h2></div></div></div><p>Eureka can be made even more resilient and available by running
multiple instances and asking them to register with each other. In
fact, this is the default behaviour, so all you need to do to make it
work is add a valid <code class="literal">serviceUrl</code> to a peer, e.g.</p><p><b>application.yml (Two Peer Aware Eureka Servers).&nbsp;</b>
</p><pre class="screen">---
spring:
  profiles: peer1
eureka:
  instance:
    hostname: peer1
  client:
    serviceUrl:
      defaultZone: http://peer2/eureka/

---
spring:
  profiles: peer2
eureka:
  instance:
    hostname: peer2
  client:
    serviceUrl:
      defaultZone: http://peer1/eureka/</pre><p>
</p><p>In this example we have a YAML file that can be used to run the same
server on 2 hosts (peer1 and peer2), by running it in different
Spring profiles. You could use this configuration to test the peer
awareness on a single host (there&#8217;s not much value in doing that in
production) by manipulating <code class="literal">/etc/hosts</code> to resolve the host names. In
fact, the <code class="literal">eureka.instance.hostname</code> is not needed if you are running
on a machine that knows its own hostname (it is looked up using
<code class="literal">java.net.InetAddress</code> by default).</p><p>You can add multiple peers to a system, and as long as they are all
connected to each other by at least one edge, they will synchronize
the registrations amongst themselves. If the peers are physically
separated (inside a data centre or between multiple data centres) then
the system can in principle survive split-brain type failures.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_prefer_ip_address" href="#_prefer_ip_address"></a>2.6&nbsp;Prefer IP Address</h2></div></div></div><p>In some cases, it is preferable for Eureka to advertise the IP Adresses
of services rather than the hostname.  Set <code class="literal">eureka.instance.preferIpAddress</code>
to <code class="literal">true</code> and when the application registers with eureka, it will use its
IP Address rather than its hostname.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Tip"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="images/tip.png"></td><th align="left">Tip</th></tr><tr><td align="left" valign="top"><p>If hostname can&#8217;t be determined by Java, then IP address is sent to Eureka.
Only explict way of setting hostname is by using <code class="literal">eureka.instance.hostname</code>.
You can set your hostname at the run time using environment variable, for
example <code class="literal">eureka.instance.hostname=${HOST_NAME}</code>.</p></td></tr></table></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi__service_discovery_eureka_clients.html">Prev</a>&nbsp;</td><td width="20%" align="center">&nbsp;</td><td width="40%" align="right">&nbsp;<a accesskey="n" href="multi__circuit_breaker_hystrix_clients.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">1.&nbsp;Service Discovery: Eureka Clients&nbsp;</td><td width="20%" align="center"><a accesskey="h" href="multi_spring-cloud-netflix.html">Home</a></td><td width="40%" align="right" valign="top">&nbsp;3.&nbsp;Circuit Breaker: Hystrix Clients</td></tr></table></div></body></html>