如何解决“Serverless”系统的冷启动问题

{"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","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"就像生活中所有的美好事物一样,Serverless(无服务器)也有其缺点。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"其中一个缺点就是臭名昭著的“冷启动”("},{"type":"link","attrs":{"href":"https:\/\/en.wikipedia.org\/wiki\/Cold_start_(recommender_systems)","title":null,"type":null},"content":[{"type":"text","text":"Cold Start"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":")。在本文中,我们将介绍“冷启动”是什么,影响 Serverless 启动延迟的因素有哪些,以及如何减轻它们对应用程序的影响。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"什么是冷启动?"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"“冷启动”是指函数服务于特定调用请求时的状态。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"Serverless 函数由一个或多个微容器提供。当某个请求传入时,我们的函数将会检查是否已有某个容器正在运行来为该调用提供服务。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"当某个空闲容器已经可用时,我们称之为“热”(“warm”)容器。如果没有现成的容器,函数将启动一个新的容器,这就是我们所说的“冷启动”。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"当处于“冷态”(Cold State)的函数被调用时,完成请求将需要额外的时间,因为启动新容器会有延迟。这就是冷启动的问题:它们使得应用程序的响应变慢了。在21世纪的“即时时代”(instant-age),这可能是一个大问题。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"冷启动是怎样工作的?"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/static001.geekbang.org\/infoq\/7a\/7ab51a7d4b01c3c35afbfb857eeebf21.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"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","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"现在,我们已经知道了什么是“冷启动”,那么让我们深入了解一下它们的工作原理。其内部工作原理可能会因你所使用的服务(AWS Lambda、Azure Functions等)或开源项目(OpenFaas、Kubeless、OpenWhisk等)的不同而不同,但一般来说,这些原则适用于所有的 Serverless 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容器提供服务之后,该容器通常能保持活动状态并允许空闲一段时间。容器编排系统将根据其参数来决定是否关闭以及何时关闭该容器。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"这是一种权衡:保持容器处于活动状态将能节省启动资源并加快后续的请求速度,但会增加空闲的时间成本。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"AWS Lambda 通常能使容器“保活”(保持活动状态)30-45 分钟。有时还不止这些(特别是对于在 VPC 内运行的 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我的意思是,速度能提高100倍,这是很重要的;"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"VPC:在虚拟私有云中运行的函数会有额外的延迟,通常要多一到两秒才能启动;尝试着将你的函数设计为运行于 VPC 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每当它的性能低于预期时,查看日志并确定代码的哪些部分导致了性能的下降。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https:\/\/aws.amazon.com\/xray\/","title":null,"type":null},"content":[{"type":"text","text":"AWS X-Ray"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 和 "},{"type":"link","attrs":{"href":"https:\/\/dashbird.io\/","title":null,"type":null},"content":[{"type":"text","text":"Dashbird"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 等服务支持这种开箱即用的分析,能为你在性能优化过程中节省大量的时间。 如果你在专业项目的生产环境中运行 Serverless 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函数通常有一个处理程序(Handler)方法\/函数作为底层基础设施和代码之间的接口。该函数通常会将一个事件和上下文作为参数传递给我们的函数,然后神奇的事情就发生了。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"有趣的是,我们可以在这个方法\/函数之外运行代码。假设每次调用我们的函数时,它都需要导入一个相同的三方库,或者可能从外部持久化存储中获取对象。我们可以在调用处理程序方法\/函数之前在处理程序外部执行这些操作,而不是在调用处理程序方法\/函数之后再执行这些操作。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"只要容器保持活动状态,在处理程序之外声明并执行的所有内容都将保留在容器的内存中。当它再次被调用时(从“热”状态),数据的导入或获取将不需要再次运行,可以直接从内存中获取并使用它们,从而加快了代码的执行时间。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"这不会加快冷启动,但会减少后续请求的启动时间。总的来说,我们的应用程序将会有更好的性能。"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"压缩程序包的大小"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"当我们为 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