One-way and two-way doors
On This Lesson 4 topics
This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.
In this lesson
spend design effort where reversal is expensive.
Planned topics
- Two-way door: easy to reverse (a library, an internal endpoint); decide fast.
- One-way door: costly to reverse (public API, data model, shard key, cloud vendor); decide carefully.
- Reversibility can be bought: feature flags, abstraction at the right place, expand-and-contract migrations.
- Common failure: slow on reversible things, fast on irreversible ones.
Draft outline details
Demonstration
a list of order-subsystem decisions sorted into doors with a reversal cost estimate.
Check your understanding
Which decision deserves more analysis, a shard key or a logging library?
Show answer
The shard key; it is a one-way door.
Practice
Apply this lesson with the module's lab, exercises and quiz.
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