architecture-decision-records

Architecture Decision Records

Workflow Protocol

1. Determine the next ADR number by scanning docs/internal/adr/ for existing ADRs.
2. Run the decision-ledger read gate before drafting:

/trace-history --risk High --last 20. Include relevant prior decisions, or state that no relevant high-risk prior decision was found.

1. Gather context by reading related code and existing ADRs.
2. Guide the user through the decision by asking clarifying questions if the title alone is insufficient.
3. Generate the ADR following the template below.
4. Save the ADR to docs/internal/adr/ADR-[NNN]-[slug].md.
5. Update the Index Table in docs/technical/DECISIONS.md.

When to write an ADR vs skip

| Write ADR | Skip ADR | |---|---| | New framework/database adoption | Minor version upgrades | | API design patterns | Bug fixes | | Security architecture | Implementation details | | Integration patterns | Routine maintenance |

ADR lifecycle

Proposed → Accepted → Deprecated → Superseded
              ↓
           Rejected

Template (MADR format — use this)

# ADR-NNN: [Title]

## Status
Accepted | Proposed | Deprecated | Superseded by ADR-NNN

## Context
[Problem statement, current situation, constraints, scale]

## Prior Decision Check
[Result of `/trace-history --risk High --last 20`; cite relevant prior entries
or state "No relevant prior high-risk decisions found."]

## Decision Drivers
- [Must/Should/Could requirement]

## Considered Options
### Option 1: [Name] — [one-line summary]
Pros: ... | Cons: ...

### Option 2: [Name]
Pros: ... | Cons: ...

## Decision
We will use **[Option N]** because [key rationale].

## Consequences
**Positive:** ...
**Negative:** ...
**Risks:** ... Mitigation: ...

## Related ADRs
- ADR-NNN: [relationship]

Quick examples

Lightweight ADR (for clear-cut decisions):

# ADR-0012: Adopt TypeScript for Frontend

**Status**: Accepted | **Date**: 2024-01-15 | **Deciders**: @alice, @bob

## Context
50+ React components with prop-type-mismatch bugs. PropTypes are runtime-only.

## Decision
TypeScript for all new frontend code. Migrate incrementally with `allowJs: true`.

## Consequences
Good: Compile-time errors, better IDE support.
Bad: Learning curve, initial slowdown.

Y-Statement (for concise formal record):

In the context of **building a microservices architecture**,
facing **need for centralized auth and rate limiting**,
we decided for **Kong Gateway**
and against **AWS API Gateway and custom Nginx**,
to achieve **vendor independence and plugin extensibility**,
accepting **we manage Kong infrastructure ourselves**.

File structure

docs/internal/adr/
├── ADR-0001-use-postgresql.md
└── ADR-0003-mongodb-deprecated.md  # [SUPERSEDED by ADR-0020]

Index table (maintain in docs/technical/DECISIONS.md)

| ADR | Title | Status | Date | |---|---|---|---| | 0001 | Use PostgreSQL | Accepted | 2024-01-10 | | 0003 | MongoDB for profiles | Deprecated | 2023-06-15 |

Key rules

• Never modify accepted ADRs — write a new one to supersede
• Write early — before implementation starts, not after
• Max 1-2 pages — if longer, decision scope is too broad
• State real cons — an ADR without honest tradeoffs has no value
• Update status — mark deprecated when superseded; link the new ADR

Automation

# Custom repo path:
# 1. Create docs/internal/adr/ADR-[NNN]-[slug].md
# 2. Append one summary row and one summary entry to docs/technical/DECISIONS.md
# 3. Do not overwrite docs/technical/DECISIONS.md; it is append-only