Documenting Architectural Decisions

Technical decisions made today will be questioned tomorrow by new team members, auditors, or your future self. Architecture Decision Records (ADRs) capture not just what was decided, but why, what alternatives were considered, and what consequences to expect.

ADR Benefits

ADR Format

Standard Template

ARCHITECTURE DECISION RECORD TEMPLATE
═════════════════════════════════════

# ADR-[NUMBER]: [TITLE]

## Status
[Proposed | Accepted | Deprecated | Superseded by ADR-XXX]

## Date
[YYYY-MM-DD when decided]

## Context
[What is the situation? What problem are we trying to solve?
What constraints do we have? What forces are at play?]

## Decision
[What is the decision we're making? Be clear and specific.]

## Alternatives Considered

### Alternative 1: [Name]
- Pros: [list]
- Cons: [list]
- Why not chosen: [reason]

### Alternative 2: [Name]
- Pros: [list]
- Cons: [list]
- Why not chosen: [reason]

## Consequences

### Positive
- [benefit 1]
- [benefit 2]

### Negative
- [drawback 1]
- [drawback 2]

### Risks
- [risk and mitigation]

## Related Decisions
- [ADR-XXX: Related decision]

## References
- [Links to relevant documentation, RFCs, etc.]

Real Example

# ADR-005: Use PostgreSQL for Primary Database

## Status
Accepted

## Date
2024-01-15

## Context
We need to select a primary database for our SaaS application.
Requirements:
- Strong consistency for financial transactions
- Complex queries for analytics
- JSON support for flexible schemas
- Proven reliability at scale
- Team familiarity
- Reasonable operational complexity

Current team has experience with MySQL and PostgreSQL.
Expected load: 10K transactions/day initially, scaling to 1M+.

## Decision
Use PostgreSQL 16 as our primary database, deployed on 
AWS RDS with Multi-AZ configuration.

## Alternatives Considered

### Alternative 1: MySQL
- Pros: Team familiarity, simple setup, good performance
- Cons: Weaker JSON support, fewer advanced features
- Why not chosen: JSON support critical for our schema needs

### Alternative 2: MongoDB
- Pros: Flexible schema, good for documents
- Cons: Eventual consistency concerns for transactions
- Why not chosen: Need strong consistency for financial data

### Alternative 3: CockroachDB
- Pros: Distributed by design, PostgreSQL compatible
- Cons: Complexity overkill for current scale, cost
- Why not chosen: Premature optimization for our scale

## Consequences

### Positive
- Strong ecosystem with extensive tooling
- JSONB support for flexible portions of schema
- Excellent query planner for complex analytics
- Team can leverage existing PostgreSQL knowledge
- RDS simplifies operations

### Negative
- Horizontal scaling will require read replicas or sharding
- Not ideal for time-series data (may need separate solution)
- RDS costs higher than self-managed

### Risks
- Scale ceiling: Mitigate with read replicas, caching layer
- Vendor lock-in to RDS: Acceptable trade-off for reduced ops

## Related Decisions
- ADR-012: TimescaleDB for metrics data
- ADR-003: Redis for caching layer

## References
- PostgreSQL docs: https://postgresql.org/docs/16/
- AWS RDS pricing analysis: [internal doc]

When to Create ADRs

Decision Criteria

CREATE AN ADR WHEN:
═══════════════════

HIGH IMPACT:
├── Affects multiple services/components
├── Difficult or expensive to reverse
├── Significant development effort
├── Team had substantial debate
└── External stakeholder interest

EXAMPLES:
├── Choosing a database
├── Selecting a framework
├── Defining API architecture
├── Choosing authentication approach
├── Deciding deployment strategy
├── Establishing coding standards
├── Picking cloud provider
└── Defining data retention policy

DON'T NEED ADR:
├── Choosing variable names
├── Minor library selection
├── Bug fix approaches
├── UI component styling
└── Easily reversible choices

ADR Workflow

ADR CREATION WORKFLOW
═════════════════════

STEP 1: Identify Decision
├── Significant technical choice ahead
├── Team has different opinions
├── Will affect future development
└── Worth documenting

STEP 2: Draft ADR
├── Author creates draft
├── Includes context and constraints
├── Lists alternatives considered
├── Proposes decision
└── Status: "Proposed"

STEP 3: Review
├── Share with affected teams
├── Collect feedback (comments/PR)
├── Technical discussion
├── May revise based on input
└── Time-box: 1 week typical

STEP 4: Decide
├── Team meeting or async vote
├── Make final decision
├── Update ADR with decision
└── Status: "Accepted"

STEP 5: Communicate
├── Announce decision
├── Link from relevant code/docs
├── Reference in implementation PRs
└── Add to onboarding materials

Organizing ADRs

Folder Structure

ADR ORGANIZATION
════════════════

IN REPOSITORY:
─────────────────────────────────────
project/
├── docs/
│   └── adr/
│       ├── README.md (index)
│       ├── 0001-record-architecture-decisions.md
│       ├── 0002-use-typescript.md
│       ├── 0003-graphql-api-design.md
│       ├── 0004-microservices-vs-monolith.md
│       └── 0005-postgresql-database.md
├── src/
└── ...

README.md INDEX:
─────────────────────────────────────
# Architecture Decision Records

| # | Title | Status | Date |
|---|-------|--------|------|
| 1 | Record architecture decisions | Accepted | 2024-01-01 |
| 2 | Use TypeScript | Accepted | 2024-01-05 |
| 3 | GraphQL API design | Accepted | 2024-01-10 |
| 4 | Microservices vs monolith | Accepted | 2024-01-15 |
| 5 | PostgreSQL database | Accepted | 2024-01-15 |

NUMBERING:
├── Sequential: 0001, 0002, 0003...
├── Never reuse numbers
├── Deprecated ADRs keep numbers
└── Superseded points to replacement

In GitScrum NoteVault

ADRS IN NOTEVAULT
═════════════════

ORGANIZATION:
├── Create "Architecture Decisions" space
├── Tag ADRs with #adr
├── Link to related projects
├── Link to implementation tasks
└── Search across all ADRs

LINKING:
├── ADR → Task that implements it
├── Task → ADR that explains why
├── Project → Key ADRs
└── Bidirectional references

TEMPLATES:
├── Save ADR template in NoteVault
├── Create new ADR from template
├── Consistent structure
└── Required fields enforced

Maintaining ADRs

Lifecycle Management

ADR LIFECYCLE
═════════════

PROPOSED:
├── Draft stage
├── Open for discussion
├── Not yet decided
└── May be rejected

ACCEPTED:
├── Decision made
├── Implementation can proceed
├── Reference in code
└── Most common final state

DEPRECATED:
├── No longer relevant
├── Technology changed
├── Business changed
├── Keep for history
└── Note why deprecated

SUPERSEDED:
├── Replaced by newer ADR
├── Link to replacement
├── Original still valuable for history
└── "Superseded by ADR-XXX"

EXAMPLE:
# ADR-003: Use REST API
## Status
Superseded by ADR-015 (GraphQL migration)

[Original content preserved for history]

Best Practices

For ADRs

1. Write at decision time — Context fresh
2. Keep them short — Focused on decision
3. Store with code — Easy to find
4. Never delete — History matters
5. Reference in code — Link implementation

Anti-Patterns

ADR MISTAKES:
✗ Writing months after decision
✗ Too long (multiple pages)
✗ Storing separately from code
✗ Deleting deprecated ADRs
✗ No alternatives documented
✗ No consequences listed
✗ No review process
✗ Never referenced again

Related Solutions

• Documenting project decisions in NoteVault
• Developer knowledge base
• Building knowledge-sharing teams