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2016-03-02-Nginx负载均衡.html
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<h2 id="正向代理"><a href="#正向代理" class="headerlink" title="正向代理"></a>正向代理</h2><p>====</p>
<p>场景：在国内是无法正常使用google.com。如果想要访问google.com，可以购买一台国外的服务器A，此时你和服务器A的网络是相通的。而服务器A又跟google.com相通， 此时可以由服务器A代理你（客户端），去访问google.com。这个过程称之为正向代理，服务端（google.com）只需要知道代理服务器的ip，不需要知道客户端的ip。 <img src="http://www.dhu021.top/wp-content/uploads/2018/10/正向代理.png" alt=""> 结论：正向代理，是用于代理客户端的。</p>
<h2 id="反向代理"><a href="#反向代理" class="headerlink" title="反向代理"></a>反向代理</h2><p>====</p>
<p>场景：当一个服务器接受过多来自客户端的请求时，服务器难以处理和响应这些请求，会使得整个系统性能下降。为了解决这个难题，可以提供多台部署相同应用的服务器，让客户端的请求分别发送到不同的服务器上，这样单机服务器的压力就会降低很多，整体性能便会提升。但是有一个问题，每个服务器ip都是不同的，也就是说客户端的请求要发送到多个不同的ip上。让客户手动指定ip进行请求，这种方式很不明智。首先是客户的随机性，不知道会访问哪台服务器，其次，会造成一部分服务器压力大，一部分服务器几乎没有使用，浪费资源。因此，这里就需要一个角色去代理服务器，让客户端的请求直接发送到这个角色上，由这个角色去分发请求到不同的服务器上。 这个角色就是反向代理服务器。 <img src="http://www.dhu021.top/wp-content/uploads/2018/10/反向代理.png" alt=""> 结论：反向代理，是用于代理服务端的。</p>
<h2 id="负载均衡"><a href="#负载均衡" class="headerlink" title="负载均衡"></a>负载均衡</h2><p>====</p>
<p>场景：反向代理过程中，每台服务器处理来自客户端的请求都应该是均衡的。 原理：使用一个反向代理服务器指向多台部署相同应用的服务器，客户端请求直接向反向代理服务器发起，反向代理服务器根据负载均衡机制，将请求转发到不同的应用服务器上。 负载均衡机制： <img src="http://www.dhu021.top/wp-content/uploads/2018/10/负载均衡.png" alt=""></p>
<h2 id="Nginx负载均衡方法"><a href="#Nginx负载均衡方法" class="headerlink" title="Nginx负载均衡方法"></a>Nginx负载均衡方法</h2><p>===========</p>
<p>Nginx负载均衡（工作在七层“应用层”）功能主要是通过upstream模块实现，Nginx负载均衡默认对后端服务器有健康检测的能力，仅限于端口检测，在后端服务器比较少的情况下负载均衡能力表现突出。 1、轮询（默认） 每个请求按时间顺序逐一分配到不同的后端服务器，如果后端某台服务器宕机，则自动剔除故障机器，使用户访问不受影响。 2、weight 指定轮询权重，weight值越大，分配到的几率就越高，主要用于后端每台服务器性能不均衡的情况。 3、ip_hash 每个请求按访问IP的哈希结果分配，这样每个访客固定访问一个后端服务器，可以有效的解决动态网页存在的session共享问题。 4、fair（第三方） 更智能的一个负载均衡算法，此算法可以根据页面大小和加载时间长短智能地进行负载均衡，也就是根据后端服务器的响应时间来分配请求，响应时间短的优先分配。如果想要使用此调度算法，需要Nginx的upstream_fair模块。 5、url_hash（第三方） 按访问URL的哈希结果来分配请求，使每个URL定向到同一台后端服务器，可以进一步提高后端缓存服务器的效率。如果想要使用此调度算法，需要Nginx的hash软件包。 在upstream模块中，可以通过server命令指定后端服务器的IP地址和端口，同时还可以设置每台后端服务器在负载均衡调度中的状态，常用的状态有以下几种： 1、down 表示当前server暂时不参与负载均衡。 2、backup 预留的备份机，当其他所有非backup机器出现故障或者繁忙的时候，才会请求backup机器，这台机器的访问压力最轻。 3、max_fails 允许请求的失败次数，默认为1，配合fail_timeout一起使用 4、fail_timeout 经历max_fails次失败后，暂停服务的时间，默认为10s（某个server连接失败了max_fails次，则nginx会认为该server不工作了。同时，在接下来的 fail_timeout时间内，nginx不再将请求分发给失效的server。）<br><figure class="highlight nginx"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line">http</span><br><span class="line">{</span><br><span class="line"> <span class="attribute">upstream</span> whsirserver </span><br><span class="line"> {</span><br><span class="line"> <span class="attribute">server</span> <span class="number">192.168.0.120:80</span> weight=<span class="number">5</span> max_fails=<span class="number">3</span> fail_timeout=<span class="number">20s</span>;</span><br><span class="line"> <span class="attribute">server</span> <span class="number">192.168.0.121:80</span> weight=<span class="number">1</span> max_fails=<span class="number">3</span> fail_timeout=<span class="number">20s</span>;</span><br><span class="line"> <span class="attribute">server</span> <span class="number">192.168.0.122:80</span> weight=<span class="number">3</span> max_fails=<span class="number">3</span> fail_timeout=<span class="number">20s</span>;</span><br><span class="line"> <span class="attribute">server</span> <span class="number">192.168.0.123:80</span> weight=<span class="number">4</span> max_fails=<span class="number">3</span> fail_timeout=<span class="number">20s</span>;</span><br><span class="line"> }</span><br><span class="line"> server</span><br><span class="line"> {</span><br><span class="line"> <span class="attribute">listen</span> <span class="number">80</span>;</span><br><span class="line"> <span class="attribute">server_name</span> blog.whsir.com;</span><br><span class="line"> <span class="attribute">index</span> index.html index.htm;</span><br><span class="line"> <span class="attribute">root</span> /data/www;</span><br><span class="line"> <span class="attribute">location</span> / </span><br><span class="line"> {</span><br><span class="line"> <span class="attribute">proxy_pass</span> http://whsirserver;</span><br><span class="line"> <span class="attribute">proxy_next_upstream</span> http_500 http_502 <span class="literal">error</span> timeout invalid_header;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>upstream负载均衡开始，通过upstream指定了一个负载均衡器的名称为whsirserver，这个名称可以自己定义，在后面proxy_pass直接调用即可。 proxy_next_upstream参数用来定义故障转移策略，当后端服务器节点返回500、502和执行超时等错误时，自动将请求转发到upstream负载均衡器中的另一台服务器，实现故障转移。 nginx提供了以下三种方法： 1）round-robin：请求以循环、轮转的方式分发到服务器 2）least-connected：下一个请求被分配到拥有最少活动连接数的服务器 3）ip-hash：使用一个哈希函数，基于客户端ip地址判断下一个请求应该被分发到哪台服务器</p>
<h2 id="相关配置说明"><a href="#相关配置说明" class="headerlink" title="相关配置说明"></a>相关配置说明</h2><hr>
<p>1）循环、轮转负载均衡 round-robin：默认情况下，使用循环、轮转的方式分发请求到服务器。 当不指定负载均衡方式时，默认以round-robin方式实现。所有请求都会被代理到myapp服务器，根据负载均衡机制分发请求。 配置示例：<br><figure class="highlight axapta"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">http{</span><br><span class="line"> upstream myapp{</span><br><span class="line"> <span class="keyword">server</span> srv1.example.com;</span><br><span class="line"> <span class="keyword">server</span> srv2.example.com;</span><br><span class="line"> <span class="keyword">server</span> srv3.example.com;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">server</span>{</span><br><span class="line"> listen <span class="number">80</span>;</span><br><span class="line"> location / {</span><br><span class="line"> proxy_pass http:<span class="comment">//myapp;</span></span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>2）最少连接负载均衡 least-connected：当一些请求处理的时间比较长时，最少连接负载均衡能够争取到更大的公平。 配置示例：<br><figure class="highlight routeros"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">upstream myapp{</span><br><span class="line"> least-conn;</span><br><span class="line"> <span class="built_in"> server </span>srv1.example.com;</span><br><span class="line"> <span class="built_in"> server </span>srv2.example.com;</span><br><span class="line"> <span class="built_in"> server </span>srv3.example.com;</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>3）基于ip地址的负载均衡 ip-hash：采用目标地址散列调度（Destination Hashing Scheduling）算法，根据请求的目标ip地址，作为散列键（Hash Key）从静态分配的散列表找出对应的服务器，若该服务器可用且未超载，则将请求发送带服务器，否则返回空。<br><figure class="highlight routeros"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">upstream myapp{</span><br><span class="line"> ip-hash;</span><br><span class="line"> <span class="built_in"> server </span>srv1.example.com;</span><br><span class="line"> <span class="built_in"> server </span>srv2.example.com;</span><br><span class="line"> <span class="built_in"> server </span>srv3.example.com;</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>1.单纯使用Nginx，会造成配置维护成本变高。 2.单点故障率增加，因为热点服务的访问量很高，如果这个服务的负载均衡服务出现问题，整个服务都会挂掉。</p>
<h2 id="Nginx配置说明"><a href="#Nginx配置说明" class="headerlink" title="Nginx配置说明"></a>Nginx配置说明</h2><p>=========<br><figure class="highlight axapta"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#user nobody;</span></span><br><span class="line">worker_processes <span class="number">4</span>;</span><br><span class="line">events {</span><br><span class="line"> <span class="meta"># 最大并发数</span></span><br><span class="line"> worker_connections <span class="number">1024</span>;</span><br><span class="line">}</span><br><span class="line">http{</span><br><span class="line"> <span class="meta"># 待选服务器列表</span></span><br><span class="line"> upstream myproject{</span><br><span class="line"> <span class="meta"># ip_hash指令，将同一用户引入同一服务器。</span></span><br><span class="line"> ip_hash;</span><br><span class="line"> <span class="keyword">server</span> <span class="number">125.219</span><span class="number">.42</span><span class="number">.4</span> fail_timeout=<span class="number">60</span>s;</span><br><span class="line"> <span class="keyword">server</span> <span class="number">172.31</span><span class="number">.2</span><span class="number">.183</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">server</span>{</span><br><span class="line"> <span class="meta"># 监听端口</span></span><br><span class="line"> listen <span class="number">80</span>;</span><br><span class="line"> <span class="meta"># 根目录下</span></span><br><span class="line"> location / {</span><br><span class="line"> <span class="meta"># 选择哪个服务器列表</span></span><br><span class="line"> proxy_pass http:<span class="comment">//myproject;</span></span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
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<script type="text/javascript" src="/js/src/bootstrap.js?v=5.1.4"></script>
<script type="text/javascript">
// Popup Window;
var isfetched = false;
var isXml = true;
// Search DB path;
var search_path = "search.xml";
if (search_path.length === 0) {
search_path = "search.xml";
} else if (/json$/i.test(search_path)) {
isXml = false;
}
var path = "/" + search_path;
// monitor main search box;
var onPopupClose = function (e) {
$('.popup').hide();
$('#local-search-input').val('');
$('.search-result-list').remove();
$('#no-result').remove();
$(".local-search-pop-overlay").remove();
$('body').css('overflow', '');
}
function proceedsearch() {
$("body")
.append('<div class="search-popup-overlay local-search-pop-overlay"></div>')
.css('overflow', 'hidden');
$('.search-popup-overlay').click(onPopupClose);
$('.popup').toggle();
var $localSearchInput = $('#local-search-input');
$localSearchInput.attr("autocapitalize", "none");
$localSearchInput.attr("autocorrect", "off");
$localSearchInput.focus();
}
// search function;
var searchFunc = function(path, search_id, content_id) {
'use strict';
// start loading animation
$("body")
.append('<div class="search-popup-overlay local-search-pop-overlay">' +
'<div id="search-loading-icon">' +
'<i class="fa fa-spinner fa-pulse fa-5x fa-fw"></i>' +
'</div>' +
'</div>')
.css('overflow', 'hidden');
$("#search-loading-icon").css('margin', '20% auto 0 auto').css('text-align', 'center');
$.ajax({
url: path,
dataType: isXml ? "xml" : "json",
async: true,
success: function(res) {
// get the contents from search data
isfetched = true;
$('.popup').detach().appendTo('.header-inner');
var datas = isXml ? $("entry", res).map(function() {
return {
title: $("title", this).text(),
content: $("content",this).text(),
url: $("url" , this).text()
};
}).get() : res;