增加轮询负载均衡

[twomiao]

hi，你好

GatewayWorker 负载均衡模式随机性分配，导致每个worker 服务连接负载不均匀，有的进程连接数比较少，有的连接数比较多。
所以扩展了一下轮询负载均衡，Nginx 默认也是轮询负载均衡。

测试代码：
并发连接数 5000，测试负载均衡是否均匀。

增加负载均衡模式两种：随机，轮询（已更改为默认）

// 设置轮询
Gateway::$selectLoadBalancingMode = Gateway::ROUTER_ROUND_ROBIN;

// 设置随机
Gateway::$selectLoadBalancingMode = Gateway::ROUTER_RANDOM;

测试负载均衡结果如下：

随机负载均衡：
{
"127.0.0.1:ChatBusinessWorker:28": 180,
"127.0.0.1:ChatBusinessWorker:22": 160,
"127.0.0.1:ChatBusinessWorker:12": 144,
"127.0.0.1:ChatBusinessWorker:16": 151,
"127.0.0.1:ChatBusinessWorker:31": 150,
"127.0.0.1:ChatBusinessWorker:13": 146,
"127.0.0.1:ChatBusinessWorker:15": 164,
"127.0.0.1:ChatBusinessWorker:24": 163,
"127.0.0.1:ChatBusinessWorker:25": 169,
"127.0.0.1:ChatBusinessWorker:18": 157,
"127.0.0.1:ChatBusinessWorker:29": 142,
"127.0.0.1:ChatBusinessWorker:6": 168,
"127.0.0.1:ChatBusinessWorker:3": 153,
"127.0.0.1:ChatBusinessWorker:26": 148,
"127.0.0.1:ChatBusinessWorker:21": 134,
"127.0.0.1:ChatBusinessWorker:9": 131,
"127.0.0.1:ChatBusinessWorker:27": 155,
"127.0.0.1:ChatBusinessWorker:30": 173,
"127.0.0.1:ChatBusinessWorker:23": 169,
"127.0.0.1:ChatBusinessWorker:1": 156,
"127.0.0.1:ChatBusinessWorker:4": 154,
"127.0.0.1:ChatBusinessWorker:20": 156,
"127.0.0.1:ChatBusinessWorker:7": 146,
"127.0.0.1:ChatBusinessWorker:17": 149,
"127.0.0.1:ChatBusinessWorker:10": 162,
"127.0.0.1:ChatBusinessWorker:19": 163,
"127.0.0.1:ChatBusinessWorker:5": 147,
"127.0.0.1:ChatBusinessWorker:2": 163,
"127.0.0.1:ChatBusinessWorker:8": 162,
"127.0.0.1:ChatBusinessWorker:11": 164,
"127.0.0.1:ChatBusinessWorker:14": 166,
"127.0.0.1:ChatBusinessWorker:0": 155
}

// 可见随机的劣势，最小值131，最大值180，分配不均衡导致性能问题。

轮询负载均衡：
{
"127.0.0.1:ChatBusinessWorker:24": 157,
"127.0.0.1:ChatBusinessWorker:13": 157,
"127.0.0.1:ChatBusinessWorker:29": 157,
"127.0.0.1:ChatBusinessWorker:11": 157,
"127.0.0.1:ChatBusinessWorker:30": 157,
"127.0.0.1:ChatBusinessWorker:20": 157,
"127.0.0.1:ChatBusinessWorker:4": 157,
"127.0.0.1:ChatBusinessWorker:18": 157,
"127.0.0.1:ChatBusinessWorker:10": 156,
"127.0.0.1:ChatBusinessWorker:0": 156,
"127.0.0.1:ChatBusinessWorker:1": 156,
"127.0.0.1:ChatBusinessWorker:28": 156,
"127.0.0.1:ChatBusinessWorker:21": 156,
"127.0.0.1:ChatBusinessWorker:2": 156,
"127.0.0.1:ChatBusinessWorker:7": 156,
"127.0.0.1:ChatBusinessWorker:3": 156,
"127.0.0.1:ChatBusinessWorker:14": 156,
"127.0.0.1:ChatBusinessWorker:19": 156,
"127.0.0.1:ChatBusinessWorker:17": 156,
"127.0.0.1:ChatBusinessWorker:26": 156,
"127.0.0.1:ChatBusinessWorker:6": 156,
"127.0.0.1:ChatBusinessWorker:22": 156,
"127.0.0.1:ChatBusinessWorker:9": 156,
"127.0.0.1:ChatBusinessWorker:15": 156,
"127.0.0.1:ChatBusinessWorker:27": 156,
"127.0.0.1:ChatBusinessWorker:16": 156,
"127.0.0.1:ChatBusinessWorker:25": 156,
"127.0.0.1:ChatBusinessWorker:5": 156,
"127.0.0.1:ChatBusinessWorker:8": 156,
"127.0.0.1:ChatBusinessWorker:12": 156,
"127.0.0.1:ChatBusinessWorker:23": 156,
"127.0.0.1:ChatBusinessWorker:31": 156
}

从结果来看轮询负载均衡能够好分配连接到业务逻辑服务器，不会出现某些业务服务器空闲，有些繁忙。
可自定义选择使用随机，轮询，我已经修改默认为轮询均衡分配连接给BusinessWorker服务器。

// array_search(min($roundRobinRecord), $roundRobinRecord, true);
使用最小值就是方便分布式部署新的服务器进程上线空闲，这时候连接上线初始化连接为0，
Gateway根据内部轮询表判断哪台服务器连接数少就分配给谁，这样达到连接数最终均衡的目的。

[walkor]

感谢pr