深入浅出kubernetes之WorkQueue详解

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"WorkQueue称为工作队列，Kubernetes的WorkQueue队列与普通FIFO（先进先出，First-In, First-Out）队列相比，实现略显复杂，它的主要功能在于标记和去重，并支持如下特性。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"有序"},{"type":"text","text":"：按照添加顺序处理元素（item）。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"去重"},{"type":"text","text":"：相同元素在同一时间不会被重复处理，例如一个元素在处理之前被添加了多次，它只会被处理一次。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"并发性"},{"type":"text","text":"：多生产者和多消费者。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"标记机制"},{"type":"text","text":"：支持标记功能，标记一个元素是否被处理，也允许元素在处理时重新排队。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"通知机制"},{"type":"text","text":"：ShutDown方法通过信号量通知队列不再接收新的元素，并通知metric goroutine退出。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"延迟"},{"type":"text","text":"：支持延迟队列，延迟一段时间后再将元素存入队列。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"限速"},{"type":"text","text":"：支持限速队列，元素存入队列时进行速率限制。限制一个元素被重新排队（Reenqueued）的次数。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"Metric"},{"type":"text","text":"：支持metric监控指标，可用于Prometheus监控。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"WorkQueue支持3种队列，并提供了3种接口，不同队列实现可应对不同的使用场景，分别介绍如下。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"Interface"},{"type":"text","text":"：FIFO队列接口，先进先出队列，并支持去重机制。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"DelayingInterface"},{"type":"text","text":"：延迟队列接口，基于Interface接口封装，延迟一段时间后再将元素存入队列。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"RateLimitingInterface"},{"type":"text","text":"：限速队列接口，基于DelayingInterface接口封装，支持元素存入队列时进行速率限制。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"size","attrs":{"size":16}},{"type":"strong"}],"text":"FIFO队列"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"FIFO队列支持最基本的队列方法，例如插入元素、获取元素、获取队列长度等。另外，WorkQueue中的限速及延迟队列都基于Interface接口实现，其提供如下方法："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"代码路径：vendor/k8s.io/client-go/util/workqueue/queue.go"}]},{"type":"codeblock","attrs":{"lang":"go"},"content":[{"type":"text","text":"type Interface interface {\n Add(item interface{})\n Len() int\n Get() (item interface{}, shutdown bool)\n Done(item interface{})\n ShutDown()\n ShuttingDown() bool\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"FIFO队列Interface方法说明如下。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"Add"},{"type":"text","text":"：给队列添加元素（item），可以是任意类型元素。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"Len"},{"type":"text","text":"：返回当前队列的长度。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"Get"},{"type":"text","text":"：获取队列头部的一个元素。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"Done"},{"type":"text","text":"：标记队列中该元素已被处理。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"ShutDown"},{"type":"text","text":"：关闭队列。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"ShuttingDown"},{"type":"text","text":"：查询队列是否正在关闭。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"FIFO队列数据结构如下："}]},{"type":"codeblock","attrs":{"lang":"go"},"content":[{"type":"text","text":"type Type struct {\n queue []t\n dirty set\n processing set\n cond *sync.Cond\n shuttingDown bool\n metrics queueMetrics\n unfinishedWorkUpdatePeriod time.Duration\n clock clock.Clock\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"FIFO队列数据结构中最主要的字段有queue、dirty和processing。其中queue字段是实际存储元素的地方，它是slice结构的，用于保证元素有序；dirty字段非常关键，除了能保证去重，还能保证在处理一个元素之前哪怕其被添加了多次（并发情况下），但也只会被处理一次；processing 字段用于标记机制，标记一个元素是否正在被处理。应根据WorkQueue的特性理解源码的实现，FIFO存储过程如图5-9所示。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c2/c26387cb10ca582ba63b2243afeac1bd.png","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":"center","origin":null},"content":[{"type":"text","text":"图5-9  FIFO存储过程"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通过Add方法往FIFO队列中分别插入1、2、3这3个元素，此时队列中的queue和dirty字段分别存有1、2、3元素，processing字段为空。然后通过Get方法获取最先进入的元素（也就是1元素），此时队列中的queue和dirty字段分别存有2、3元素，而1元素会被放入processing字段中，表示该元素正在被处理。最后，当我们处理完1元素时，通过Done方法标记该元素已经被处理完成，此时队列中的processing字段中的1元素会被删除。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如图5-9所示，这是FIFO队列的存储流程，在正常的情况下，FIFO队列运行在并发场景下。高并发下如何保证在处理一个元素之前哪怕其被添加了多次，但也只会被处理一次？下面进行讲解，FIFO并发存储过程如图5-10所示。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c7/c7ad23223a54b105e45c4107e747d3ca.png","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":"center","origin":null},"content":[{"type":"text","text":" 图5-10  FIFO并发存储过程"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":"center","origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如图5-10所示，在并发场景下，假设goroutine A通过Get方法获取1元素，1元素被添加到processing字段中，同一时间，goroutine B通过Add方法插入另一个1元素，此时在processing字段中已经存在相同的元素，所以后面的1元素并不会被直接添加到queue字段中，当前FIFO队列中的dirty字段中存有1、2、3元素，processing字段存有1元素。在goroutine A通过Done方法标记处理完成后，如果dirty字段中存有1元素，则将1元素追加到queue字段中的尾部。需要注意的是，dirty和processing字段都是用Hash Map数据结构实现的，所以不需要考虑无序，只保证去重即可。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"size","attrs":{"size":16}},{"type":"strong"}],"text":"延迟队列"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"延迟队列，基于FIFO队列接口封装，在原有功能上增加了AddAfter方法，其原理是延迟一段时间后再将元素插入FIFO队列。延迟队列数据结构如下："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"代码路径：vendor/k8s.io/client-go/util/workqueue/delaying_queue.go"}]},{"type":"codeblock","attrs":{"lang":"go"},"content":[{"type":"text","text":"type DelayingInterface interface {\n Interface\n AddAfter(item interface{}, duration time.Duration)\n}\n\ntype delayingType struct {\n Interface\n clock clock.Clock\n stopCh chan struct{}\n heartbeat clock.Ticker\n waitingForAddCh chan *waitFor\n metrics retryMetrics\n deprecatedMetrics retryMetrics\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"AddAfter方法会插入一个item（元素）参数，并附带一个duration（延迟时间）参数，该duration参数用于指定元素延迟插入FIFO队列的时间。如果duration小于或等于0，会直接将元素插入FIFO队列中。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"delayingType结构中最主要的字段是waitingForAddCh，其默认初始大小为1000，通过AddAfter方法插入元素时，是非阻塞状态的，只有当插入的元素大于或等于1000时，延迟队列才会处于阻塞状态。waitingForAddCh字段中的数据通过goroutine运行的waitingLoop函数持久运行。延迟队列运行原理如图5-11所示。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/b1/b16ca44c74aa2070e943d261867da534.png","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":"center","origin":null},"content":[{"type":"text","text":"图5-11  延迟队列运行原理"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":"center","origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如图5-11所示，将元素1放入waitingForAddCh字段中，通过waitingLoop函数消费元素数据。当元素的延迟时间不大于当前时间时，说明还需要延迟将元素插入FIFO队列的时间，此时将该元素放入优先队列（waitForPriorityQueue）中。当元素的延迟时间大于当前时间时，则将该元素插入FIFO队列中。另外，还会遍历优先队列（waitForPriorityQueue）中的元素，按照上述逻辑验证时间。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"size","attrs":{"size":16}},{"type":"strong"}],"text":"限速队列"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"限速队列，基于延迟队列和FIFO队列接口封装，限速队列接口（RateLimitingInterface）在原有功能上增加了AddRateLimited、Forget、NumRequeues方法。限速队列的重点不在于RateLimitingInterface接口，而在于它提供的4种限速算法接口（RateLimiter）。其原理是，限速队列利用延迟队列的特性，延迟某个元素的插入时间，达到限速目的。RateLimiter数据结构如下："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"代码路径：vendor/k8s.io/client-go/util/workqueue/default_rate_limiters.go"}]},{"type":"codeblock","attrs":{"lang":"go"},"content":[{"type":"text","text":"type RateLimiter interface {\n When(item interface{}) time.Duration\n Forget(item interface{})\n NumRequeues(item interface{}) int\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"限速队列接口方法说明如下。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"When"},{"type":"text","text":"：获取指定元素应该等待的时间。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"Forget"},{"type":"text","text":"：释放指定元素，清空该元素的排队数。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"NumRequeues"},{"type":"text","text":"：获取指定元素的排队数。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/60/60dfa0099a827284df3b3e9a42e1aa36.png","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面会分别详解WorkQueue提供的4种限速算法，应对不同的场景，这4种限速算法分别如下。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"令牌桶算法（BucketRateLimiter）。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"排队指数算法（ItemExponentialFailureRateLimiter）。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"计数器算法（ItemFastSlowRateLimiter）。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"混合模式（MaxOfRateLimiter），将多种限速算法混合使用。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"1. 令牌桶算法"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"令牌桶算法是通过Go语言的第三方库golang.org/x/time/rate实现的。令牌桶算法内部实现了一个存放token（令牌）的“桶”，初始时“桶”是空的，token会以固定速率往“桶”里填充，直到将其填满为止，多余的token会被丢弃。每个元素都会从令牌桶得到一个token，只有得到token的元素才允许通过（accept），而没有得到token的元素处于等待状态。令牌桶算法通过控制发放token来达到限速目的。令牌桶算法原理如图5-12所示。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/6a/6a049ef23bcdc8b542bed2782b0d82a7.png","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":"center","origin":null},"content":[{"type":"text","text":"图5-12  令牌桶算法原理"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":"center","origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"WorkQueue在默认的情况下会实例化令牌桶，代码示例如下："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"go"},"content":[{"type":"text","text":"rate.NewLimiter(rate.Limit(10), 100)"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在实例化rate.NewLimiter后，传入r和b两个参数，其中r参数表示每秒往“桶”里填充的token数量，b参数表示令牌桶的大小（即令牌桶最多存放的token数量）。我们假定r为10，b为100。假设在一个限速周期内插入了1000个元素，通过r.Limiter.Reserve().Delay函数返回指定元素应该等待的时间，那么前b（即100）个元素会被立刻处理，而后面元素的延迟时间分别为item100/100ms、item101/200ms、item102/300ms、item103/400ms，以此类推。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"2. 排队指数算法"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"排队指数算法将相同元素的排队数作为指数，排队数增大，速率限制呈指数级增长，但其最大值不会超过maxDelay。元素的排队数统计是有限速周期的，一个限速周期是指从执行AddRateLimited方法到执行完Forget方法之间的时间。如果该元素被Forget方法处理完，则清空排队数。排队指数算法的核心实现代码示例如下："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"代码路径：vendor/k8s.io/client-go/util/workqueue/default_rate_limiters.go"}]},{"type":"codeblock","attrs":{"lang":"go"},"content":[{"type":"text","text":"r.failures[item] = r.failures[item] + 1\nbackoff := float64(r.baseDelay.Nanoseconds()) * math.Pow(2, float64(exp))\nif backoff > math.MaxInt64 {\n return r.maxDelay\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"该算法提供了3个主要字段：failures、baseDelay、maxDelay。其中，failures字段用于统计元素排队数，每当AddRateLimited方法插入新元素时，会为该字段加1；另外，baseDelay字段是最初的限速单位（默认为5ms），maxDelay字段是最大限速单位（默认为1000s）。排队指数增长趋势如图5-13所示。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/34/34c1cfab9dfb032236df58ab11d95ce5.png","alt":null,"title":"","style":[{"key":"width","value":"50%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":"center","origin":null},"content":[{"type":"text","text":"图5-13  排队指数增长趋势"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":"center","origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"限速队列利用延迟队列的特性，延迟多个相同元素的插入时间，达到限速目的。"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ad/adf83563816720d3b0dca4b34491293a.png","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我们假定baseDelay是1 * time.Millisecond，maxDelay是1000 * time.Second。假设在一个限速周期内通过AddRateLimited方法插入10个相同元素，那么第1个元素会通过延迟队列的AddAfter方法插入并设置延迟时间为1ms（即baseDelay），第2个相同元素的延迟时间为2ms，第3个相同元素的延迟时间为4ms，第4个相同元素的延迟时间为8ms，第5个相同元素的延迟时间为16ms……第10个相同元素的延迟时间为512ms，最长延迟时间不超过1000s（即maxDelay）。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"3. 计数器算法"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"计数器算法是限速算法中最简单的一种，其原理是：限制一段时间内允许通过的元素数量，例如在1分钟内只允许通过100个元素，每插入一个元素，计数器自增1，当计数器数到100的阈值且还在限速周期内时，则不允许元素再通过。但WorkQueue在此基础上扩展了fast和slow速率。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"计数器算法提供了4个主要字段：failures、fastDelay、slowDelay及maxFastAttempts。其中，failures字段用于统计元素排队数，每当AddRateLimited方法插入新元素时，会为该字段加1；而fastDelay和slowDelay字段是用于定义fast、slow速率的；另外，maxFastAttempts字段用于控制从fast速率转换到slow速率。计数器算法核心实现的代码示例如下："}]},{"type":"codeblock","attrs":{"lang":"text"},"content":[{"type":"text","text":"r.failures[item] = r.failures[item] + 1\nif r.failures[item] <= r.maxFastAttempts {\n return r.fastDelay\n}\nreturn r.slowDelay"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"假设fastDelay是5 * time.Millisecond，slowDelay是10 * time.Second，maxFastAttempts是3。在一个限速周期内通过AddRateLimited方法插入4个相同的元素，那么前3个元素使用fastDelay定义的fast速率，当触发maxFastAttempts字段时，第4个元素使用slowDelay定义的slow速率。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"4. 混合模式"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"混合模式是将多种限速算法混合使用，即多种限速算法同时生效。例如，同时使用排队指数算法和令牌桶算法，代码示例如下："}]},{"type":"codeblock","attrs":{"lang":"go"},"content":[{"type":"text","text":"func DefaultControllerRateLimiter() RateLimiter {\n return NewMaxOfRateLimiter(\n NewItemExponentialFailureRateLimiter(5*time.Millisecond, 1000*time.Second),\n &BucketRateLimiter{Limiter: rate.NewLimiter(rate.Limit(10), 100)},\n )\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/14/144c8a519a432e8d1af766f9fb5cb652.jpeg","alt":null,"title":"","style":[{"key":"width","value":"25%"},{"key":"bordertype","value":"none"}],"href":"https://u.jd.com/3K5DNZ","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本文选自《Kubernetes源码剖析》一书"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"郑东旭著"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"电子工业出版社出版"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"购买链接：https://u.jd.com/3K5DNZ"}]}]}