ribbon已經提供了很多負載的策略，如下圖：

這些負載策略通常已經滿足我們的日常業務需求（這些策略的具體介紹，可以點此檢視），如特殊需要，我們也需要自定義負載策略。

我的應用場景是：spring cloud zuul做為使用者請求的入口服務，zuul代理到目標服務的時候，其內部就是通過ribbon的負載策略選出並代理到一個服務例項，這裡我自定義的負載策略實現的功能是“同一個ip下的同一個使用者的所有請求被代理到同一個例項”（如果請求沒有使用者資訊，那就相當於ip_hash策略）。

新建一個類IpUserHashRule繼承自com.netflix.loadbalancer.AbstractLoadBalancerRule：

public class IpUserHashRule extends AbstractLoadBalancerRule {
	
	private static Logger log = LoggerFactory.getLogger(IpUserHashRule.class);
	
	public Server choose(ILoadBalancer lb, Object key) {
        if (lb == null) {
            log.warn("no load balancer");
            return null;
        }

        Server server = null;
        int count = 0;
        while (server == null && count++ < 10) {
            List<Server> reachableServers = lb.getReachableServers();
            List<Server> allServers = lb.getAllServers();
            int upCount = reachableServers.size();
            int serverCount = allServers.size();

            if ((upCount == 0) || (serverCount == 0)) {
                log.warn("No up servers available from load balancer: " + lb);
                return null;
            }

            int nextServerIndex = ipUserHash(serverCount);
            server = allServers.get(nextServerIndex);

            if (server == null) {
                /* Transient. */
                Thread.yield();
                continue;
            }

            if (server.isAlive() && (server.isReadyToServe())) {
                return (server);
            }

            // Next.
            server = null;
        }

        if (count >= 10) {
            log.warn("No available alive servers after 10 tries from load balancer: "
                    + lb);
        }
        return server;

    }

	private int ipUserHash(int serverCount) {
        String userTicket = getTicketFromCookie();
        String userIp = getRemoteAddr();
        try {
        	userIp = InetAddress.getLocalHost().getHostAddress();
		} catch (UnknownHostException e) {
		}
        int userHashCode = Math.abs((userIp+userTicket).hashCode());
		return userHashCode%serverCount;
	}

	private String getRemoteAddr() {
		RequestContext ctx = RequestContext.getCurrentContext();
		HttpServletRequest request = ctx.getRequest();
		String remoteAddr = "0.0.0.0";
        if (request.getHeader("X-FORWARDED-FOR") != null) {
            remoteAddr = request.getHeader("X-FORWARDED-FOR");
        } else {
            remoteAddr = request.getRemoteAddr();
        }
        return remoteAddr;
	}

	private String getTicketFromCookie() {
		String ticket = "";
		RequestContext ctx = RequestContext.getCurrentContext();
		HttpServletRequest request = ctx.getRequest();
		//從cookie獲取ticket
        Cookie cookie = CookieUtil.getCookieByName(request,CookieUtil.COOKIE_TICKET_NAME);
        if (cookie!=null) {
            ticket = cookie.getValue()!=null?cookie.getValue():"";
        }
		return ticket;
	}

	@Override
	public Server choose(Object key) {
		return choose(getLoadBalancer(), key);
	}

	@Override
	public void initWithNiwsConfig(IClientConfig clientConfig) {
		// TODO Auto-generated method stub
		
	}
	public static void main(String[] args) {
		String ticket = "";
		String localIp = "127.0.0.1";
		System.out.println(Math.abs((ticket+localIp).hashCode())%5);
	}

}
 

有了這個類過後，還需要配置使用這個自定義的負載策略，配置如下：

user.ribbon.NFLoadBalancerRuleClassName=com.bqjr.spring.cloud.zuul.ribbonextend.IpUserHashRule

醬紫就可以啦。

參考文件：http://docs.springcloud.cn/user-guide/ribbon/#ribbon-api

推薦文章（Netflix 原始碼分析）：http://www.idouba.net/sping-cloud-and-netflix/