Architecture Documentation, ADRs, and Runbooks

Documentation explains how a system works, why a decision was made, and what to do first during an outage. Diagram freshness, decision records, and operational procedures should share one ownership model.

Quick Decision

Need	Document	Watch out
Explain system boundaries	Context/container/component diagram	Include source and review date
Explain request or event flow	Sequence/data-flow diagram	Show sync/async boundaries
Record an architecture choice	ADR	State decision, alternatives, and outcome
Repeat an operation safely	Runbook	Include preconditions, commands, rollback
Catalog services	Service map	Owner, SLO, dependencies, and data owner

Production Checklist

• Problem: Which decision or operational step does the document accelerate?
• Solution: Are owner, audience, scope, last-reviewed date, and source of truth clear?
• Trade-off: Detailed documentation is valuable; stale documentation creates false confidence.
• Failure mode: Handle stale diagrams, missing rollback, wrong alert steps, and hidden dependencies.
• Measurement: Track ADR review age, runbook success, incident MTTR, and broken links.
• Security/cost: Do not put secrets, private endpoints, or customer data in documents.

Architecture Views

Maintain these views when needed:

• Context: Users, external systems, and system boundary.
• Container/service: Services, queues, databases, caches, and ownership.
• Component: Modules inside a critical service and dependency direction.
• Sequence: Success, error/retry, async completion, and failover flows.
• Data flow: Movement from source of truth to projections, cache, backups, or analytics.

Every arrow should be meaningful through a protocol or event name, timeout/retry boundary, and failure boundary. Keep Mermaid diagrams easy to update; reduce drift with diagrams-as-code or source links when infrastructure changes.

Service Map and API Catalog

A service map should show owner/team, repository, runtime, region, SLO, data owner, inbound/outbound dependencies, auth method, deployment method, and alert links. An API catalog adds endpoint/schema owner, lifecycle, version, rate limits, examples, and deprecation date.

Use the same service ID across API Contracts and Tooling, observability, and incident processes.

ADR Format

An ADR is a short, durable decision record:

# ADR-0042: Use a queue for order completion
Status: Accepted
Date: 2026-09-03
Context: The work exceeds the request latency budget.
Decision: Use queue + worker + job status.
Alternatives: Synchronous call, scheduled batch
Consequences: Eventual consistency, retry, and DLQ operations

An ADR is not a copy of the implementation or a long tutorial. Its status may evolve through proposed, accepted, deprecated, and superseded; link a new decision rather than silently deleting the old one.

Runbook Design

Every runbook should follow this order:

1. Impact: Which users, SLO, or region is affected?
2. Signal: Where are the alert, dashboard, logs, and traces?
3. Safety: Authorization, blast radius, maintenance window, and stop conditions.
4. Diagnosis: Lowest-risk checks first.
5. Mitigation: Actions and expected signals.
6. Recovery: Rollback, replay, failover, or traffic shift.
7. Verification: Validate SLO, errors, queue age, and user flow.
8. Follow-up: Incident record, ADR, or permanent fix.

Use placeholders and dry-run output for commands; never include passwords, tokens, or broad destructive commands. Exercise runbooks regularly with production access owners.

Lifecycle

A code or infrastructure change should update its diagram, service map, ADR, or runbook in the same review. Quarterly reviews, post-incident validation, and broken-link checks reduce stale documents. Remove documents that no longer carry decision or operational value after cleaning their links.