adr-architecture

name

adr-architecture

description

Documents significant architectural and technical decisions with full context, alternatives considered, trade-offs analyzed, and consequences understood. Creates a decision trail that helps teams understand why decisions were made. Use when choosing between technology options, making infrastructure decisions, establishing standards, migrating systems, or when user mentions ADR, architecture decision, technical decision record, or decision documentation.

Architecture Decision Records (ADR)

Table of Contents

• Workflow
  • 1. Understand the Decision
  • 2. Choose ADR Template
  • 3. Document the Decision
  • 4. Validate Quality
  • 5. Deliver and File
• Common Patterns
• Guardrails
• Quick Reference

Each ADR captures: Context (what situation necessitates this decision), Decision (what we're choosing), Alternatives (other options considered), Consequences (trade-offs and implications), and Status (proposed, accepted, deprecated, superseded).

Quick Example:

# ADR-042: Use PostgreSQL for Primary Database

**Status:** Accepted
**Date:** 2024-01-15
**Deciders:** Backend team, CTO

## Context
Need to select primary database for new microservices platform.
Requirements: ACID transactions, complex queries, 10k+ QPS at launch.

## Decision
Use PostgreSQL 15+ as primary relational database.

## Alternatives Considered
- MySQL: Weaker JSON support, less robust constraint handling
- MongoDB: No ACID across documents, eventual consistency issues
- CockroachDB: Excellent but adds operational complexity we can't support yet

## Consequences
✓ Strong consistency and data integrity
✓ Excellent JSON support for semi-structured data
✓ Team has deep PostgreSQL experience
✗ Vertical scaling limits (will need read replicas at 50k+ QPS)
✗ More complex to shard than DynamoDB if we need it

Workflow

Copy this checklist and track your progress:

ADR Progress:
- [ ] Step 1: Understand the decision
- [ ] Step 2: Choose ADR template
- [ ] Step 3: Document the decision
- [ ] Step 4: Validate quality
- [ ] Step 5: Deliver and file

Step 1: Understand the decision

Gather decision context: what decision needs to be made, why now, who decides, constraints (budget, timeline, skills, compliance), requirements (functional, non-functional, business), and scope (one service vs organization-wide). This ensures the ADR addresses the right problem.

Step 2: Choose ADR template

For technology selection (frameworks, libraries, databases) → Use resources/template.md. For complex architectural decisions with multiple interdependent choices → Study resources/methodology.md. To see examples → Review resources/examples/ (database-selection.md, microservices-migration.md, api-versioning.md).

Step 3: Document the decision

Create adr-{number}-{short-title}.md with: clear title, metadata (status, date, deciders), context (situation and requirements), decision (specific and actionable), alternatives considered (with pros/cons), consequences (trade-offs, risks, benefits), implementation notes if relevant, and links to related ADRs. See Common Patterns for decision-type specific guidance.

Step 4: Validate quality

Self-check using resources/evaluators/rubric_adr_architecture.json. Verify: context explains WHY, decision is specific and actionable, 2-3+ alternatives documented with trade-offs, consequences include benefits AND drawbacks, technical details accurate, understandable to unfamiliar readers, honest about downsides. Minimum standard: Score ≥ 3.5 (aim for 4.5+ if controversial/high-impact).

Step 5: Deliver and file

Present the completed ADR file, highlight key trade-offs identified, suggest ADR numbering if not provided, recommend review process for high-stakes decisions, and note any follow-up decisions needed. Filing convention: Store ADRs in docs/adr/ or architecture/decisions/ directory with sequential numbering.

Common Patterns

For technology selection:

• Focus on technical capabilities vs requirements
• Include performance benchmarks if available
• Document team expertise level
• Consider operational complexity

For architectural changes:

• Include migration strategy in consequences
• Document backward compatibility impact
• Consider team velocity impact during transition
• Note monitoring and rollback plans

For standards and conventions:

• Include examples of the standard in practice
• Document exceptions or escape hatches
• Consider enforcement mechanisms
• Note educational/onboarding implications

For deprecations:

• Set status to "Deprecated" or "Superseded"
• Link to superseding ADR
• Document sunset timeline
• Include migration guide

Guardrails

Do:

• Be honest about trade-offs (every choice has downsides)
• Write for future readers who lack current context
• Include specific technical details (versions, configurations)
• Acknowledge uncertainty and risks
• Keep ADRs immutable (status changes, but content doesn't)
• Write one ADR per decision (focused scope)

Don't:

• Make decisions sound better than they are
• Omit alternatives that were seriously considered
• Use jargon without explanation
• Write vague consequences ("might improve performance")
• Revisit/edit old ADRs (write new superseding ADR instead)
• Combine multiple independent decisions in one ADR

Quick Reference

• Standard template: resources/template.md
• Complex decisions: resources/methodology.md
• Examples: resources/examples/database-selection.md, resources/examples/microservices-migration.md, resources/examples/api-versioning.md
• Quality rubric: resources/evaluators/rubric_adr_architecture.json

ADR Naming Convention: adr-{number}-{short-kebab-case-title}.md

• Example: adr-042-use-postgresql-for-primary-database.md