本文使用nodejs作为微服务API网关，从而将消费端的请求，随机路由到一个可用的服务节点上。核心代码如下：

本文参考了《架构探险》轻量级服务架构
本文示例代码：node-zookeeper-demo

var express = require('express');
var zookeeper = require('node-zookeeper-client');
var httpProxy = require('http-proxy');
var cluster = require('cluster');
var os = require('os');
var cache = {};

var CPUS = os.cpus().length;

var PORT = 8084;
var CONNECTION_STRING = '127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183';
var REGISTRY_ROOT = '/registry';

var app = express();

if (cluster.isMaster) {
    for (var i = 0; i < CPUS; i++) {
        cluster.fork();
    }
}
else {
    //连接zookeeper
    var zk = zookeeper.createClient(CONNECTION_STRING);
    zk.connect();

    //创建代理服务器对象并监听错误事件
    var proxy = httpProxy.createProxyServer();
    proxy.on('error', function (err, req, res) {
        res.end();//输出空白响应数据
    });

    //启动web服务器
    app.use(express.static('public'));
    app.all('*', function (req, res) {
        //处理图标请求
        if (req.path == '/favicon.ico') {
            res.end();
            return;
        }
        //获取服务名称
        var serviceName = req.get('Service-Name');
        
        console.log('ServiceName:%s', serviceName);
        if (!serviceName) {
            console.log('Service-Name request header is not exist');
            res.end();
            return;
        }
        //获取服务路径
        var servicePath = REGISTRY_ROOT + "/" + serviceName;
        console.log('ServicePath:%s', servicePath);
        console.log('cache[serviceName]:'+JSON.stringify(cache));
        if (cache[serviceName]) {
        //if(false){
            //TODO
            /*zk.exists(servicePath, function (event) {
                if (event.NODE_DELETED) {
                    cache = {};
                }
            }, function (error, stat) {
                if (stat) {

                }
            })*/
            console.log("-----------cache---------------"+cache[serviceName]);
            proxy.web(req, res, {
                target: 'http://' + cache[serviceName] //目标地址
            });

        }
        else {

            //获取服务路径下的地址节点
            zk.getChildren(servicePath, function (error, addressNodes) {
                if (error) {
                    console.log(error.stack);
                    res.end();
                    return;
                }
                var size = addressNodes.length;
                if (size == 0) {
                    console.log('address node is not exist');
                    res.end();
                    return;
                }
                //生成地址容器
                var addressPath = servicePath + "/";
                if (size == 1) {
                    //若只有唯一地址，则获取该地址
                    addressPath += addressNodes[0];
                } else {
                    //若存在多个地址，则随机获取一个地址
                    addressPath += addressNodes[parseInt(Math.random() * size)];
                }
                console.log('addressPath:%s', addressPath);
                //获取服务地址
                zk.getData(addressPath, function (err, serviceAddress) {
                    if (error) {
                        console.log(error.stack);
                        res.end();
                        return;
                    }
                    console.log('serviceAddress:%s', serviceAddress);
                    if (!serviceAddress) {
                        console.log('serviceAddress is not exist');
                        res.end();
                        return;
                    }

                    cache[serviceName] = serviceAddress;
                    console.log("cache"+  serviceName+": "+cache[serviceName]);

                    //执行反向代理
                    proxy.web(req, res, {
                        target: 'http://' + serviceAddress //目标地址
                    });
                });

            });
        }

    });

    app.listen(PORT, function () {
        console.log('server is running at %d', PORT);
    });
}

使用supervisor app-gateway.js启动API网关后：(supervisor可以定时监听文件的变化，代码更新无需重启)

启动网关

当然也需要启动在上文《基于ZooKeeper的服务注册实现》提到的两个客户端，让服务在ZooKeeper上注册。

测试页面

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
</head>
<body>
<div id="console"></div>
<div id="container">
    <h1>
        hello world
    </h1>
</div>
<button id="btn" >点我一下调用服务</button>

</body>
<script src="js/jquery-2.2.3.min.js"></script>
<script>
    $(function () {
        $("#btn").click(function () {
            //alert("hello world");
            $.ajax({
                method: 'GET',
                url: '/hello',
                headers: {
                    'Service-Name': 'HelloService'
                },
                success: function (data) {
                    $("#console").text(data);
                }
            })
        });

    })
</script>
</html>

点击测试按钮，在界面服务的显示运行结果"Hello"

运行结果

AB测试(Apache Bench)模拟1000个用户每次并发100请求：
注 ：在测试前，将serviceName设为固定值：var serviceName='HelloService'

AB测试

阅读本文，请结合上篇文章《基于ZooKeeper的服务注册实现》进行理解。