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14 天用 Agent 搭一条 AI 短剧生产线

D8 工作流引擎：把流水线做成可断点续跑的任务图

• 什么时候该自己写调度，什么时候该直接上现成的工作流引擎？When should you write your own scheduler, and when should you adopt an off-the-shelf workflow engine?

  国内高频海外高频基础#architecture#build-vs-buy#workflow-engine

  分析过程 · 先想清楚再作答

  1. 这题考的是技术选型的成熟度。两个极端都会被扣分：什么都自己写显得不懂杠杆，什么都上框架显得没判断力。面试官想听的是你的切换信号是什么。
  2. 先给一条通用判据：自己写的收益是理解和贴合，框架的收益是省掉你还没遇到的那些问题。所以决策取决于「你现在需要的功能有多少落在框架的核心能力上」。
  3. 自己写划算的情形：单机、节点数是个位数、路径是你定死的、需要的只是拓扑排序加幂等加状态落盘这几件事。这时候自己写不到三百行，而且换来的理解是通用的——你会彻底搞懂幂等键为什么要包含依赖指纹、状态为什么必须每步落盘。
  4. 该换的三个信号：一是开始需要跨机器调度，自己实现分布式调度的复杂度是指数级上升的；二是开始需要人工介入节点，流程要挂起几小时甚至几天，状态必须外置到数据库而不是一个 JSON 文件；三是开始需要给非工程师看和操作，那你需要的其实是一个带界面的产品。
  5. 反过来说，过早引入重型框架的代价很具体：每一个业务改动都要先绕过它的抽象，而它的收益要等规模上来才兑现。这是典型的成本前置、收益后置。
  6. 可预期的追问是「自己写的那一套能不能平滑迁走」。答：能，前提是你从一开始就把节点定义成纯声明（依赖、输入、产物、执行体），调度和状态不侵入业务。这样迁移时改的是引擎，不是六个节点。

  How to reason about it · think before answering

  1. This tests selection maturity. Both extremes lose points: building everything yourself shows no sense of leverage, adopting a framework for everything shows no judgment. The interviewer wants your switching signals.
  2. Give a general criterion: writing it yourself buys understanding and fit; a framework buys you past problems you have not hit yet. So the decision hinges on how much of what you need overlaps with the framework's core.
  3. Writing your own pays off when: single machine, a handful of nodes, a path you fixed yourself, and you only need topological ordering plus idempotency plus state persistence. That is under three hundred lines, and the understanding transfers to any engine you adopt later.
  4. Three signals to switch: you need cross-machine scheduling, where rolling your own scales in complexity exponentially; you need human-in-the-loop nodes, so runs suspend for hours or days and state must live in a database rather than a JSON file; or non-engineers need to see and operate it, in which case you need a product with a UI, not an engine.
  5. Conversely, adopting a heavy framework too early has a concrete cost: every business change must route around its abstractions, while its benefits only land at scale. Cost up front, payoff deferred.
  6. Expect the follow-up 'can you migrate off your own version cleanly'. Yes, if nodes were declarative from the start — dependencies, inputs, outputs, body — with scheduling and state kept out of the business code. Then migration replaces the engine, not the nodes.

  答题要点

  • 判据是你需要的功能与框架核心能力的重叠度，不是「自研还是选型」的立场。
  • 自己写划算：单机、节点数少、路径固定，只需要拓扑排序加幂等加状态落盘。
  • 该换的三个信号：跨机器调度、人工介入导致流程长时间挂起、非工程师要操作。
  • 过早上重型框架的代价是每次业务改动都要绕过它的抽象，收益却要等规模。
  • 把节点写成纯声明，调度与状态不侵入业务，将来迁移改的是引擎而不是节点。

  Key points

  • Decide by how much your needs overlap the framework's core, not by a build-versus-buy stance.
  • Rolling your own wins on a single machine with few nodes and a fixed path, needing only topo order, idempotency and state persistence.
  • Three switching signals: cross-machine scheduling, human-in-the-loop suspension, and non-engineers needing to operate it.
  • Adopting a heavy framework early costs a detour around its abstractions on every change, with benefits deferred to scale.
  • Keep nodes declarative and scheduling non-invasive so a later migration replaces the engine, not the nodes.