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class="toctree-l1"><a class="reference internal" href="../question-and-answer/question_answer.html">Q & A</a> </li> <li class="toctree-l1"><a class="reference internal" href="../question-and-answer/interface-compatibility.html">微服务接口兼容常见问题</a> </li> </ul> </div> </div> </nav> <section data-toggle="wy-nav-shift" class="wy-nav-content-wrap"> <nav class="wy-nav-top" role="navigation" aria-label="Mobile navigation menu"> <i data-toggle="wy-nav-top" class="fa fa-bars"></i> <a href="../index.html">ServiceComb Java Chassis 开发指南</a> </nav> <div class="wy-nav-content"> <div class="rst-content"><div role="navigation" aria-label="breadcrumbs navigation"> <ul class="wy-breadcrumbs"> <li><a href="../index.html" class="icon icon-home" alt="Docs"></a> &raquo;</li> <li>服务治理功能参考 &raquo;</li> <li>负载均衡</li> <li class="wy-breadcrumbs-aside"> </li> </ul> <hr/> </div> <div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article"> <div class="section" itemprop="articleBody"> <h1 id="_1">负载均衡</h1> <h2 id="_2">场景描述</h2> <p>ServiceComb提供了非常强大的负载均衡能力。它的核心包括两部分，第一部分是DiscoveryTree，通过将微服务实例根据接口兼容性、数据中心、实例状态等分组，DiscoveryFilter是其主要组成部分；第二部分是基于Ribbon的负载均衡方案，支持随机、顺序、基于响应时间的权值等多种负载均衡路由策略IRule，以及可以支持Invocation状态的ServerListFilterExt。</p> <p>DiscoveryTree的逻辑比较复杂，可以通过下面的处理流程了解其处理过程。 <img alt="" src="../assets/loadbalance-001.png" /></p> <p>负载均衡适用于Consumer处理链，名称为loadbalance，示例如下：</p> <pre><code class="language-yaml">servicecomb: handler: chain: Consumer: default: loadbalance </code></pre> <p>POM依赖：</p> <pre><code class="language-xml"> &lt;dependency&gt; &lt;groupId&gt;org.apache.servicecomb&lt;/groupId&gt; &lt;artifactId&gt;handler-loadbalance&lt;/artifactId&gt; &lt;/dependency&gt; </code></pre> <h2 id="_3">按照数据中心信息进行路由转发</h2> <p>服务提供者和消费者都可以通过在microservice.yaml中声明自己的服务中心信息：</p> <pre><code class="language-yaml">servicecomb: datacenter: name: mydatacenter region: my-Region availableZone: my-Zone </code></pre> <p>消费者通过比较自己的数据中心信息和提供者的信息，优先将请求转发到region和availableZone都相同的实例；如果不存在，则转发到region相同的实例；如果仍然不存在，则转发到其他实例。</p> <p>这里的region和availableZone是一般性的概念，用户可以自行确定其业务含义以便应用于资源隔离的场景中。可以参见<a href="../build-provider/definition/isolate-relationship.html">微服务实例之间的逻辑隔离关系</a>，了解更多其他实例发现相关的隔离机制。</p> <p>该规则默认启用，如果不需要使用，可以通过servicecomb.loadbalance.filter.zoneaware.enabled进行关闭。数据中心信息隔离功能在ZoneAwareDiscoveryFilter实现。</p> <h2 id="_4">根据实例属性进行路由转发</h2> <p>微服务可以指定实例的属性。实例属性可以在microservice.yaml中指定，也可以通过服务中心的API进行修改。</p> <pre><code class="language-yaml">instance_description: properties: tags: tag_key: tag_value </code></pre> <p>消费者可以指定消费具备某些属性的实例，不访问其他实例</p> <pre><code class="language-yaml">servicecomb: loadbalance: provider: # 这里表示配置对名为&quot;provider&quot;的服务生效，如果是跨应用调用，则还需要加上AppID，如&quot;AppIDOfProvider:provider&quot; transactionControl: options: tags: tag_key: expected_tag_value </code></pre> <p>上面的配置表示只访问myservice所有实例中<code>tag_key</code>属性为<code>expected_tag_value</code>的实例。</p> <p>该规则需要给每个服务单独配置，未配置表示不启用该规则，不支持对于所有服务的全局配置。</p> <p>该规则默认启用，如果不需要使用，可以通过<code>servicecomb.loadbalance.filter.instanceProperty.enabled</code>进行关闭。根据实例属性进行路由转发功能在<code>InstancePropertyDiscoveryFilter</code>实现。</p> <h2 id="_5">根据实例属性值的层级进行路由转发</h2> <p>实例属性优先级匹配可以看做是针对实例属性匹配的一种逻辑扩展。</p> <p>微服务的实例属性可以定义为具备优先级的格式，通过<code>.</code>符号进行分割。</p> <pre><code class="language-yaml">instance_description: properties: KEY: a.b.c </code></pre> <p>消费者需要指定用于优先级匹配的实例属性key，默认的key为<code>environment</code>。</p> <pre><code class="language-yaml">servicecomb: loadbalance: filter: priorityInstanceProperty: key: KEY </code></pre> <p>假设某个consumer的属性值为<code>a.b.c</code>，那么将会按照<code>a.b.c</code>&gt;<code>a.b</code>&gt;<code>a</code>&gt;<code>[空]</code> 这样的优先级顺序匹配provider的实例，一旦匹配到即终止，下面的表格给出了不同情况的具体示例</p> <table> <thead> <tr> <th align="left">consumer</th> <th align="left">match priority of provider</th> </tr> </thead> <tbody> <tr> <td align="left">a.b.c</td> <td align="left">a.b.c&gt;a.b&gt;a&gt;[空]</td> </tr> <tr> <td align="left">a.b</td> <td align="left">a.b&gt;a&gt;[空]</td> </tr> <tr> <td align="left">a</td> <td align="left">a&gt;[空]</td> </tr> <tr> <td align="left">[空]</td> <td align="left">[空]</td> </tr> </tbody> </table> <blockquote> <p>注意[空]是一种特殊情况，即未设置该属性的实例</p> </blockquote> <p>该规则默认关闭，如果需要开启，可以通过<code>servicecomb.loadbalance.filter.priorityInstanceProperty.enabled</code>配置打开。该功能在<code>PriorityInstancePropertyDiscoveryFilter</code>中实现。</p> <h2 id="_6">实例隔离功能</h2> <p>开发者可以配置实例隔离的参数，以暂时屏蔽对于错误实例的访问，提升系统可靠性和性能。下面是其配置项和缺省值</p> <pre><code class="language-yaml">servicecomb: loadbalance: isolation: enabled: true errorThresholdPercentage: 0 enableRequestThreshold: 5 singleTestTime: 60000 continuousFailureThreshold: 5 maxSingleTestWindow: 60000 # 为了保证在并发情况下只有一个实例放通，会锁定放通实例。这个时间表示最大锁定时间。 minIsolationTime: 3000 # 最短隔离时间。并发情况下，实例隔离后进行中的请求可能快速刷新隔离状态，增加最短隔离时间。 recoverImmediatelyWhenSuccess：true # 放通实例，如果调用成功，立即清除统计状态，保证后续请求能够使用该实例。 2.1.3 新增。 </code></pre> <p>隔离的统计周期是1分钟。按照上面的配置，在1分钟内，如果请求总数大于5，并且连续错误超过2次，那么就会将实例隔离。 错误率默认值为0，表示不启用，可通过配置100以内的整数来启用，例如配置为20，则表示，在1分钟内，如果请求总数大于5，并且[1]错误率大于20%或者[2]连续错误超过2次，那么就会将实例隔离。 实例隔离的时间是60秒，60秒后会尝试启用实例（还需要根据负载均衡策略确定是否选中）。</p> <p>注意事项：</p> <ol> <li>2.1.2 之前的版本，当错误率达到设定值导致实例隔离后，要想恢复，需要等待隔离时间窗结束后的第一次成功请求进行周期性累加，直到总的错误率下降到设定值以下才行。 由于请求总数是触发实例隔离的门槛，若请求总数达到设定值时计算出来的错误率远大于设定值，要想恢复是需要很久的。 使用 2.1.3 及其之后的版本没有这个问题。</li> <li>ServiceComb为了检测实例状态，在后台启动类一个线程，每隔10秒检测一次实例状态（如果实例在10秒内有被访问，则不检测），如果检测失败，每次检测会将错误计数加1。这里的计数，也会影响实例隔离。</li> </ol> <p>系统缺省的实例状态检测机制是发送一个telnet指令，参考SimpleMicroserviceInstancePing的实现。如果业务需要覆盖状态检测机制，可以通过如下两个步骤完成：</p> <ol> <li>实现MicroserviceInstancePing接口</li> <li>配置SPI：增加META-INF/services/org.apache.servicecomb.serviceregistry.consumer.MicroserviceInstancePing，内容为实现类的全名</li> </ol> <p>开发者可以针对不同的微服务配置不一样的隔离策略。只需要给配置项增加服务名，例如：</p> <pre><code class="language-yaml">servicecomb: loadbalance: myservice: isolation: enabled: true errorThresholdPercentage: 20 enableRequestThreshold: 5 singleTestTime: 10000 continuousFailureThreshold: 2 </code></pre> <p><strong><em>注意：</em></strong> 多数异常都会触发隔离计数。但一般的 <code>InvocationException</code> 不会触发隔离计数。详细可以参考 <code>LoadbalanceHandler</code> 的 <code>isFailedResponse</code> 方法实现。</p> <h2 id="_7">配置路由规则</h2> <p>开发者可以通过配置项指定负载均衡策略。</p> <pre><code class="language-yaml">servicecomb: loadbalance: strategy: name: RoundRobin # Support RoundRobin,Random,WeightedResponse,SessionStickiness </code></pre> <p>开发者可以针对不同的微服务配置不一样的策略，只需要给配置项增加服务名，例如：</p> <pre><code class="language-yaml">servicecomb: loadbalance: myservice: strategy: name: RoundRobin # Support RoundRobin,Random,WeightedResponse,SessionStickiness </code></pre> <p>每种策略还有一些专属配置项，也支持针对不同微服务进行配置。</p> <ul> <li>SessionStickiness</li> </ul> <pre><code class="language-yaml">servicecomb: loadbalance: SessionStickinessRule: sessionTimeoutInSeconds: 30 # 客户端闲置时间，超过限制后选择后面的服务器 successiveFailedTimes: 5 # 客户端失败次数，超过后会切换服务器 </code></pre> <h2 id="_8">自定义</h2> <p>负载均衡模块提供的功能已经非常强大，能够通过配置支持大部分应用场景。同时它也提供了强大的扩展能力，包括DiscoveryFilter、ServerListFilterExt、ExtensionsFactory（扩展IRule，RetryHandler等）。loadbalance模块本身包含了每一个扩展的实现，这里不再详细描述如何扩展，只简单描述步骤。开发者可以自行下载ServiceComb源码进行参考。</p> <ul> <li>DiscoveryFilter</li> <li>实现DiscoveryFilter接口</li> <li> <p>配置SPI：增加META-INF/services/org.apache.servicecomb.serviceregistry.discovery.DiscoveryFilter文件，内容为实现类的全名</p> </li> <li> <p>ServerListFilterExt</p> </li> <li>实现ServerListFilterExt接口</li> <li>配置SPI：增加META-INF/services/org.apache.servicecomb.loadbalance.ServerListFilterExt文件，内容为实现类的全名</li> <li> <p>注意：这个开发说明适用于1.0.0及其以后的版本，早期的版本开发方式不同。</p> </li> <li> <p>ExtensionsFactory</p> </li> <li>实现ExtensionsFactory，并使用@Component将其发布为一个spring bean。</li> </ul> </div> </div><footer> <div class="rst-footer-buttons" role="navigation" aria-label="Footer Navigation"> <a href="intruduction.html" class="btn btn-neutral float-left" title="处理链介绍"><span class="icon icon-circle-arrow-left"></span> Previous</a> <a href="ratelimit.html" 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