document-decision

name: document-decision description: Use when choosing or revisiting an architectural technology, integration boundary, deployment strategy, or cross-cutting pattern and you need to record the rationale, trade-offs, impacted LikeC4 elements, and consequences in an ADR.

Document Architecture Decision

Overview

Capture why an architectural choice was made, what alternatives were rejected, which modeled elements it affects, and what follow-up work it creates. An ADR should stay useful months later when the original discussion is gone.

Use the standard ADR backbone:

• Status
• Context
• Decision
• Consequences

Store ADRs as ADR/NNNN-short-title.md.

When to Use

• Selecting a technology for a system, container, or component
• Choosing a boundary or interaction pattern (adapter, queue, webhook, SaaS replacement, CQRS)
• Making a deployment or resilience decision with long-term trade-offs
• Recording a decision whose rationale would otherwise be unclear later

Do not use for repository tooling, CI/CD setup, lint rules, or LikeC4 modeling workflow mechanics.

Quick Reference

Scope

• ✅ Technology selection (PostgreSQL vs MongoDB, Kong vs HAProxy)
• ✅ Structural decisions (internal service vs SaaS, queue vs sync call, adapter boundaries)
• ✅ Infrastructure choices (replication, topology, managed vs self-hosted)
• ✅ Security/integration choices with lasting consequences
• ❌ Repository structure, CI/CD, editor tooling, or diagram-authoring mechanics

Core Pattern

1. Name the decision clearly — one line that states the architectural choice.
2. Capture the forces — constraints, risks, scale, ownership, compliance, latency, migration pressure.
3. State the decision — what is chosen, where it applies, and what is explicitly out of scope.
4. List impacted elements — affected LikeC4 elements and, if useful, impacted views or deployment areas.
5. Record consequences — at least positive and negative, optionally neutral/operational consequences.
6. Add follow-up — migrations, model updates, validation, runbooks, or open questions.

Example

# ADR-0007: Choose PostgreSQL for the primary transactional store

## Status
Accepted

## Context
`{YourSystem}` needs strong transactional guarantees, relational querying, and predictable backup tooling.
The team considered MongoDB and PostgreSQL for the primary business data store.

## Decision
Use PostgreSQL for `{YourSystem}.primaryDatabase`.

## Impacted Elements
- `{YourSystem}.api`
- `{YourSystem}.primaryDatabase`
- Any view or deployment slice that documents persistence, backup, or failover

## Consequences

### Positive
- Strong ACID guarantees for transactional workflows
- Mature replication, backup, and observability ecosystem
- Clear fit for relational reporting and joins

### Negative
- Requires schema migration discipline
- Less flexible for rapidly changing document-shaped payloads
- Operational tuning may be needed as write volume grows

### Neutral
- Some JSON-heavy payloads may still remain in application-layer adapters

## Follow-up
- Update the database container technology to `PostgreSQL`
- Review replication and backup assumptions
- Validate affected views and deployment documentation

Integration with LikeC4

• Reference impacted elements by real element ID or stable descriptive name
• Mention affected views only when they are known and relevant; do not invent view IDs
• If the decision changes the model itself, follow up with the appropriate modeling skill and then validate with test-model

Useful follow-ups:

• element or boundary changes → create-element, create-relationship
• deployment consequences → model-deployment-infrastructure
• validation after changes → test-model

Common Mistakes

❌ Documenting how the diagram was edited — ADRs capture design rationale, not modeling mechanics

❌ Missing costs or risks — a decision without trade-offs reads like advocacy, not architecture

❌ No impacted elements — if readers cannot tell what parts of the model are affected, the ADR is too abstract

❌ Confusing the ADR with an implementation checklist — the ADR states the choice and its consequences; detailed execution can be follow-up work

❌ Treating a local ADR starter as an oracle — reuse the structure, not the example wording or domain content