实现灰度发布流量管理

solve()

user-service (target=5%): stable=180, canary=20 (10%)
product-service (target=20%): stable=129, canary=71 (36%)
灰度发布流量分布(traffic_log):
service          version
order-service    v1          7
product-service  v1          8
                 v2          1
user-service     v1         13
                 v2          1