architecture-decision-records

Architecture Decision Records

Comprehensive patterns for creating, maintaining, and managing Architecture Decision Records (ADRs) that capture the context and rationale behind significant technical decisions.

When to Use This Skill

• Making significant architectural decisions
• Documenting technology choices
• Recording design trade-offs
• Onboarding new team members
• Reviewing historical decisions
• Establishing decision-making processes

Core Concepts

1. What is an ADR?

An Architecture Decision Record captures:

• Context: Why we needed to make a decision
• Decision: What we decided
• Consequences: What happens as a result

2. When to Write an ADR

Write ADR	Skip ADR
New framework adoption	Minor version upgrades
Database technology choice	Bug fixes
API design patterns	Implementation details
Security architecture	Routine maintenance
Integration patterns	Configuration changes

3. ADR Lifecycle

Proposed → Accepted → Deprecated → Superseded
              ↓
           Rejected

Before drafting a standard, lightweight, or Y-statement ADR, read decision templates.

Before drafting a deprecation ADR or RFC, read deprecation and RFC templates.

ADR Management

Directory Structure

docs/
├── adr/
│   ├── README.md           # Index and guidelines
│   ├── template.md         # Team's ADR template
│   ├── 0001-use-postgresql.md
│   ├── 0002-caching-strategy.md
│   ├── 0003-mongodb-user-profiles.md  # [DEPRECATED]
│   └── 0020-deprecate-mongodb.md      # Supersedes 0003

ADR Index (README.md)

# Architecture Decision Records

This directory contains Architecture Decision Records (ADRs) for [Project Name].

## Index

| ADR                                   | Title                              | Status     | Date       |
| ------------------------------------- | ---------------------------------- | ---------- | ---------- |
| [0001](0001-use-postgresql.md)        | Use PostgreSQL as Primary Database | Accepted   | 2024-01-10 |
| [0002](0002-caching-strategy.md)      | Caching Strategy with Redis        | Accepted   | 2024-01-12 |
| [0003](0003-mongodb-user-profiles.md) | MongoDB for User Profiles          | Deprecated | 2023-06-15 |
| [0020](0020-deprecate-mongodb.md)     | Deprecate MongoDB                  | Accepted   | 2024-01-15 |

## Creating a New ADR

1. Copy `template.md` to `NNNN-title-with-dashes.md`
2. Fill in the template
3. Submit PR for review
4. Update this index after approval

## ADR Status

- **Proposed**: Under discussion
- **Accepted**: Decision made, implementing
- **Deprecated**: No longer relevant
- **Superseded**: Replaced by another ADR
- **Rejected**: Considered but not adopted

Automation (adr-tools)

# Install adr-tools
brew install adr-tools

# Initialize ADR directory
adr init docs/adr

# Create new ADR
adr new "Use PostgreSQL as Primary Database"

# Supersede an ADR
adr new -s 3 "Deprecate MongoDB in Favor of PostgreSQL"

# Generate table of contents (to a separate file, so the hand-written
# index and guidelines in README.md are not overwritten)
adr generate toc > docs/adr/toc.md

# Link related ADRs
adr link 2 "Complements" 1 "Is complemented by"

Review Process

## ADR Review Checklist

### Before Submission

- [ ] Context clearly explains the problem
- [ ] All viable options considered
- [ ] Pros/cons balanced and honest
- [ ] Consequences (positive and negative) documented
- [ ] Related ADRs linked

### During Review

- [ ] At least 2 senior engineers reviewed
- [ ] Affected teams consulted
- [ ] Security implications considered
- [ ] Cost implications documented
- [ ] Reversibility assessed

### After Acceptance

- [ ] ADR index updated
- [ ] Team notified
- [ ] Implementation tickets created
- [ ] Related documentation updated

Best Practices

Do's

• Write ADRs early - Before implementation starts
• Keep them short - 1-2 pages maximum
• Be honest about trade-offs - Include real cons
• Link related decisions - Build decision graph
• Update status - Deprecate when superseded

Don'ts

• Don't change accepted ADRs - Write new ones to supersede
• Don't skip context - Future readers need background
• Don't hide failures - Rejected decisions are valuable
• Don't be vague - Specific decisions, specific consequences
• Don't forget implementation - ADR without action is waste