Describe the bug 我跑了2个微服务都设置了权重（A服务权重为0，B服务权重为100），

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负载均衡没有按权重分流 about kitex HOT 6 CLOSED

hzxgo commented on July 24, 2024

负载均衡没有按权重分流

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Comments (6)

jizhuozhi commented on July 24, 2024 1

那我知道你这个问题在哪了，etcd实现在进行diff的时候是使用了DefaultDiff，而DefaultDiff只对addr进行了判断，这个是基于云环境下不可变实例的假设来做的，不过控制面动态修改权重确实是有效需求，DefaultDiff的逻辑我来修正下吧，cc @HeyJavaBean

https://github.com/kitex-contrib/registry-etcd/blob/8f24094a74c322f6fd3231d9a02de4d87047a93d/etcd_resolver.go#L107-L110

kitex/pkg/discovery/discovery.go

Lines 72 to 102 in f43dcb5

 // DefaultDiff provides a natural implementation for the Diff method of the Resolver interface. 

 func DefaultDiff(cacheKey string, prev, next Result) (Change, bool) { 

 ch := Change{ 

 Result: Result{ 

 Cacheable: next.Cacheable, 

 CacheKey: cacheKey, 

 Instances: next.Instances, 

 }, 

 } 

 prevMap := make(map[string]struct{}, len(prev.Instances)) 

 for _, ins := range prev.Instances { 

 prevMap[ins.Address().String()] = struct{}{} 

 } 

 nextMap := make(map[string]struct{}, len(next.Instances)) 

 for _, ins := range next.Instances { 

 addr := ins.Address().String() 

 nextMap[addr] = struct{}{} 

 if _, found := prevMap[addr]; !found { 

 ch.Added = append(ch.Added, ins) 

 } 

 } 

 for _, ins := range prev.Instances { 

 if _, found := nextMap[ins.Address().String()]; !found { 

 ch.Removed = append(ch.Removed, ins) 

 } 

 } 

 return ch, len(ch.Added)+len(ch.Removed) != 0 

 }

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HeyJavaBean commented on July 24, 2024

我觉得这个场景的需求不该通过强行设置负载均衡切留来实现
正常的解决方案是：你的服务1重启，在服务发现环节，服务1被剔除掉了，所以client的可用下游里面就没有服务1。当服务1完成重启后，重新注册回来，流量就正常分摊给5个下游了。
要达到上面的效果，你需要配合注册中心、健康检查这些手段来实现对应的代码。

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hzxgo commented on July 24, 2024

@HeyJavaBean 我现在的业务就是你说的这种方式实现的。对于不需要100%保证业务无影响的情况下这样是没问题，但是要确保重启的绝对安全还是要无业务的情况下才稳妥，所以想到了先切流量再重启。

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HeyJavaBean commented on July 24, 2024

那我感觉从负载均衡可能做不到。不过既然你能知道要下线A服务（比如你还知道他的IP什么的），你可以尝试通过kitex的自定义服务发现resolver例添加逻辑，直接判断然后拦截掉A的服务发现结果？

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jizhuozhi commented on July 24, 2024

不过从Picker创建的实现来看，权重为0的实例会被过滤掉，不会出现说流量分配到权重为0的实例的情况，可以给下Kitex初始化代码以及版本么

kitex/pkg/loadbalance/weighted_balancer.go

Lines 93 to 106 in f43dcb5

 for idx, instance := range e.Instances { 

 weight := instance.Weight() 

 if weight <= 0 { 

 klog.Warnf("KITEX: invalid weight, weight=%d instance=%s", weight, e.Instances[idx].Address()) 

 continue 

 } 

 weightSum += weight 

 instances[cnt] = instance 

 if cnt > 0 && instances[cnt-1].Weight() != weight { 

 balance = false 

 } 

 cnt++ 

 } 

 instances = instances[:cnt]

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hzxgo commented on July 24, 2024

@jizhuozhi 如下：

kitex版本：kitex --version =》v0.9.1
初始化Client：
c, err := demo.NewClient(
variable.BuildClientName(hd.name()),
client.WithMuxConnection(2),
client.WithRPCTimeout(60time.Second),
client.WithLoadBalancer(loadbalance.NewWeightedRandomBalancer()),
client.WithConnectTimeout(10time.Second),
client.WithFailureRetry(newFailurePolicy()),
client.WithResolver(reg),
)

操作流程：

2个微服务(A,B)正常启动后，ETCD里的weight都为10，此时2个微服务负载比例50%；
调整ETCD中A服务的weight=0，即使等待一会后，A服务还是会有流量，不会为0
调整ETCD中B服务的weight=9999999，A服务的weight不修改仍为10，此时流量基本都到A服务了，B服务基本没流量（目前我是采用这种方案在切流量）

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负载均衡没有按权重分流 about kitex HOT 6 CLOSED

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	// DefaultDiff provides a natural implementation for the Diff method of the Resolver interface.
	func DefaultDiff(cacheKey string, prev, next Result) (Change, bool) {
	ch := Change{
	Result: Result{
	Cacheable: next.Cacheable,
	CacheKey: cacheKey,
	Instances: next.Instances,
	},
	}

	prevMap := make(map[string]struct{}, len(prev.Instances))
	for _, ins := range prev.Instances {
	prevMap[ins.Address().String()] = struct{}{}
	}

	nextMap := make(map[string]struct{}, len(next.Instances))
	for _, ins := range next.Instances {
	addr := ins.Address().String()
	nextMap[addr] = struct{}{}
	if _, found := prevMap[addr]; !found {
	ch.Added = append(ch.Added, ins)
	}
	}

	for _, ins := range prev.Instances {
	if _, found := nextMap[ins.Address().String()]; !found {
	ch.Removed = append(ch.Removed, ins)
	}
	}
	return ch, len(ch.Added)+len(ch.Removed) != 0
	}

	for idx, instance := range e.Instances {
	weight := instance.Weight()
	if weight <= 0 {
	klog.Warnf("KITEX: invalid weight, weight=%d instance=%s", weight, e.Instances[idx].Address())
	continue
	}
	weightSum += weight
	instances[cnt] = instance
	if cnt > 0 && instances[cnt-1].Weight() != weight {
	balance = false
	}
	cnt++
	}
	instances = instances[:cnt]