如何使用 DDD 指导微服务拆分？

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"  ","attrs":{}}]},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我是架构精进之路，大厂架构师，CSDN博客专家，点击上方“关注”，坚持每天为你分享技术干货，私信我回复“01”，送你一份程序员成长进阶大礼包。  ","attrs":{}}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"软件架构发展经历","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"软件架构的发展经历了从单体架构、垂直架构、SOA架构到微服务架构以及到现在最新的service mesh（网格服务架构）的过程。借用dubbo的网站架构发展图和说明：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/35/35e443250addbb67ff5b76d2b071f5be.png","alt":"图片","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":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"微服务存在的问题","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"进入微服务之后 ， 解决了集中式架构的单体应用很多问题， 但是新的问题应运而生 ， 微服务的力度应该多大 ？微服务如何设计呢？微服务如何拆分 ？微服务边界在哪里 ？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"很长时间人们都没有解决这一问题，就连Martin Fowler在提出微服务架构的时候也没有告诉我们这该如何拆分微服务。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"甚至在很长的时间里人们对微服务拆分产生了一些误解， 有人认为：\"微服务很简单，就是将之前的单体应用拆分成多个部署包， 或者将原来的单体应用架构替换为一套支持微服务的技术架构，就算是微服务了。\" 还有人认为微服务应该拆分得越小越好。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"鉴于上述情形， 很多项目因为前期拆分过度， 导致复杂度过高， 导致后期难以运维甚至难以上线。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可以得出一个结论：","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"微服务拆分困境产生的根本原因就是不知道业务或者微服务的边界到底在什么地方。换句话说，确定了业务边界和应用边界，这个困境也就迎刃而解了。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"DDD的诞生","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"而DDD就是解决了这个确定业务边界的问题，可见DDD并不是一种技术架构，而是一种划分业务领域范围的方法论。DDD的兴起是由于很多熟悉领域驱动建模(DDD)的工程师在进行微服务设计时， 发现用DDD的思路进行业务梳理可以很好规划服务边界， 可以很好实现微服务内部和外部的\"高内聚、低耦合\"。于是越来越多的人将DDD作为业务划分的指导思想。","attrs":{}}]},{"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":"DDD是一种拆解业务、划分业务、确定业务边界的方法， 是一种高度复杂的领域设计思想，将我们的问题拆分成一个个地域， 试图分离技术实现的复杂性，主要解决的是软件难以理解难以演进的问题，DDD不是一种架构， 而是一种架构方法论， 目的就是将复杂问题领域简单化， 帮助我们设计出清晰的领域和边界， 可以很好的实现技术架构的演进。DDD包括两部分，战略设计部分和战术设计部分。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"战略设计","attrs":{}},{"type":"text","text":"主要从业务视角出发，建立业务领域模型，划分领域边界，建立通用语言的限界上下文，限界上下文可以作为微服务设计的参考边界。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"战术设计","attrs":{}},{"type":"text","text":"则从技术视角出发，侧重于领域模型的技术实现，完成软件开发和落地，包括：聚合根、实体、值对象、领域服务、应用服务和资源库等代码逻辑的设计和实现。","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"微服务拆分难题","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"开发者在刚开始尝试实现自己的微服务架构时，往往会产生一系列问题 ：","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"微服务到底应该怎么划分？","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"一个典型的微服务到底应该有多微？","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果做了微服务设计，最后真的会有好处吗？","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"回答上面的问题需要首先了解微服务设计的逻辑，","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"科学的架构设计应该通过一些输入并逐步推导出结果","attrs":{}},{"type":"text","text":"，架构师要避免凭空设计和“拍脑门”的做法。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"服务的划分有一些基本的方法和原则，通过这些方法能让微服务划分更有操作性。最终在微服务落地实施时也能按图索骥，无论是对遗留系统改造还是全新系统的架构都能游刃有余。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"微服务拆分的几个阶段","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在开始划分微服务之前，架构师需要在大脑中有一个重要的认识：","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"微服务只是手段，不是目的。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"微服务架构是为了让系统变得更容易拓展、更富有弹性。在把单体应用变成靠谱的微服务架构之前，单体系统的各个模块应该是合理、清晰地。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"也就是说，从逻辑上单体系统和微服务没有区别，某种理想情况下微服务只是把单体系统的各个模块分开部署了而已","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"大量的实践教训告诉我们，混沌的微服务架构，比解耦良好的单体应用会带来更多麻烦。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/74/74d22309b225f5de1f3d6b949bf5c0eb.webp","alt":null,"title":"混乱的微服务VS良好的单体","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":"","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}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"领域驱动设计立足于面向对象思想，从业务出发，通过领域模型的方式反映系统的抽象，从而得到合理的服务划分。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"采用 DDD 来进行业务建模和服务拆分时，可以参考下面几个阶段：","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"使用 DDD（领域驱动建模） 进行业务建模，从业务中获取抽象的模型（例如订单、用户），根据模型的关系进行划分限界上下文。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"检验模型是否得到合适的的抽象，并能反映系统设计和响应业务变化。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"从 DDD 的限界上下文往微服务转化，并得到系统架构、API列表、集成方式等产出。","attrs":{}}]}]}],"attrs":{}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/a5/a50add5987d886392b4ee5765013f97e.webp","alt":null,"title":"使用DDD划分微服务的过程\n","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"如何抽象？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"抽象需要找到看似无关事务的内在联系，对微服务的设计尤为重要。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"然而现实的例子比比皆是，电信或移动营业厅还需要用户分两步办理号卡业务、宽带业务。原始是不合适的抽象模型造成的，并最终影响了微服务的划分。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我们可以使用概念图来描述一些概念的抽象关系。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5e/5ef9169ccceb7d7e2b174fc6bc13df9f.png","alt":null,"title":"商品这一概念的概念图","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":"","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":"如果没有抽象出领域模型，就得不到正确的微服务划分。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"使用DDD进行业务建模","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通过利用DDD对系统从业务的角度分析，对系统进行抽象后，得到内聚更高的业务模型集合，在DDD中一组概念接近、高度内聚并能找到清晰的边界的业务模型被称作限界上下文（Bounded 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