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What the door metaphor means
The framework distinguishes decisions by how readily a team can return to its previous position if a choice proves wrong. Amazon’s 2015 shareholder letter describes consequential, irreversible or nearly irreversible choices as one-way doors, calling for methodical consideration and consultation. Its guidance contrasts those with decisions that can be changed and should not be slowed by the same heavyweight process. Amazon’s 2015 letter to shareholders
Amazon and AWS materials have used different door and Type 1/Type 2 numbering conventions. It is clearer to use “one-way” and “two-way” directly unless referring to a particular source’s terminology. The distinction is a decision aid, not a universal classification system or a guarantee that a choice is actually reversible.
How to tell whether an engineering choice is reversible
Ask: If this is wrong, what would it take to get back? Consider the practical undo path—not just whether code can be changed. A rollback may be technically possible while customer data, compatibility promises, operational disruption, or coordination across teams make it costly.
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| Consideration | More like a two-way door | More like a one-way door |
|---|---|---|
| Undo path | The change can be rolled back or replaced promptly. | Reversal requires migration, major rework, or cannot restore the prior state. |
| Reach | Effects are limited to a local experiment or bounded feature. | The choice commits multiple teams, customers, interfaces, data, or long-lived infrastructure. |
| Cost of error | A failure is contained and provides useful information. | A failure could have significant customer, operational, financial, or compatibility consequences. |
| Decision process | A small accountable group can act, observe, and adjust. | Evidence-gathering and consultation are warranted before committing. |
| Record | A brief note may be enough. | A significant architecture choice merits an architecture decision record. |
These are practical comparison axes drawn from Amazon and AWS guidance, not a validated scoring formula. No numeric reversibility score is established by those sources. AWS illustrates the contrast with an A/B test of a web or mobile feature as a reversible decision and building a fulfillment center or data center as a difficult-to-reverse, high-capital commitment. Those examples do not determine how every experiment or infrastructure project should be classified. AWS Executive Insights: Elements of Amazon’s Day 1 Culture
Match the decision process to the risk
For a bounded, reversible choice
Keep the decision close to the people doing the work. Make a reasoned choice, define what you will observe, and leave room to correct it. Amazon’s 2015 guidance warns that applying heavyweight analysis to every decision can create slowness, risk aversion, and fewer experiments; its 2016 letter likewise argues against using one process for every case. Amazon’s 2016 letter to shareholders
Engineering teams can sometimes make a change more reversible by limiting its initial scope, piloting it, or preserving an exit path. A feature flag or staged rollout may help contain exposure, but those are practical techniques, not a guarantee that the underlying effects—such as data changes or customer expectations—can be undone.
For a consequential, hard-to-reverse choice
Make assumptions, alternatives, and trade-offs explicit before committing. Consult the teams and stakeholders who will bear the consequences, and investigate compatibility, migration, operational, and customer effects. In Andy Jassy’s 2024 letter, he defines a two-way-door decision as one where a mistaken choice can be reversed with few, if any, ramifications. The letter also notes that the metaphor assumes doors are unlocked; that is a leadership analogy, not an engineering guarantee that constraints can always be removed. Amazon CEO Andy Jassy’s 2024 Letter to Shareholders
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AWS Executive Insights advises against waiting for 90% or more of the information when that delay would be too slow, and cites “about 70% of the information you wish you had.” This is Amazon/AWS management advice, not a measured engineering optimum or a threshold for high-consequence decisions. The same source’s claim that two-way decisions are the vast majority refers to Amazon’s context, not a measured proportion of engineering decisions generally.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Document significant architecture decisions with an ADR
An architecture decision record (ADR) captures a significant architecture choice and the reasoning around it. AWS Prescriptive Guidance describes recording the context, decision, and consequences; its examples of architecture topics include system structure, non-functional requirements, dependencies, interfaces, and construction techniques. AWS Prescriptive Guidance: Architectural decision record process
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AWS says accepted ADRs should remain immutable. If the team later changes course, create a new ADR that supersedes the earlier one rather than rewriting history. This keeps the original rationale available to people assessing how the architecture evolved. AWS Prescriptive Guidance: Using architectural decision records to streamline decision-making during development
For a consequential choice, an ADR can make the decision and its consequences visible beyond the meeting where it was made. It does not itself make a decision reversible; that depends on the actual technical and organizational exit path.
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