---
id: wiki-2026-0508-single-source-of-truth
title: Single Source of Truth (SSoT)
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [SSoT, Single Source of Truth, Authoritative Source]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [architecture, data, principle, consistency]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: typescript
  framework: redux
---

# Single Source of Truth (SSoT)

## 매 한 줄
> **"매 fact 의 1 authoritative location. Everywhere else 의 derive."**. 매 information architecture 의 fundamental principle — duplication 의 minimize 후 매 derived view 의 cache/projection 으로 처리. 매 frontend (Redux), backend (master DB), DevOps (Git as IaC source) 의 cross-cutting pattern.

## 매 핵심

### 매 layers
- **DB layer**: master DB + read replicas (no parallel sources).
- **App state**: Redux store / TanStack Query cache.
- **Config**: Git repo (Infrastructure as Code).
- **Identity**: SCIM-synced IdP (Okta/Entra).
- **Schema**: protobuf / OpenAPI as type-source.

### 매 derived view
- Materialized views (DB).
- Selectors / memoized derive (frontend).
- Search indexes (Elastic) reflecting master.
- Reporting cubes built from master.

### 매 응용
1. Redux Toolkit `createSlice` — 1 store, derived UI.
2. Git → Terraform → Cloud (no console drift).
3. SCIM provisioning — IdP authoritative.
4. CDC (Debezium) — master DB → downstream consumers.
5. Event sourcing — log as SSoT.

## 💻 패턴

### Redux normalize + selector
```typescript
import { createSlice, createSelector } from '@reduxjs/toolkit';

const usersSlice = createSlice({
  name: 'users',
  initialState: { byId: {} as Record<string, User> },
  reducers: { upsert: (state, { payload }) => { state.byId[payload.id] = payload; } },
});

export const selectUser = (id: string) => (state: RootState) => state.users.byId[id];
export const selectActiveUsers = createSelector(
  (s: RootState) => Object.values(s.users.byId),
  (users) => users.filter(u => u.active),
);
```

### Terraform as IaC SSoT
```hcl
resource "aws_s3_bucket" "logs" {
  bucket = "company-logs-prod"
  tags = { managed_by = "terraform", repo = "infra" }
}
# Console changes drift-detected via `terraform plan`
```

### Debezium CDC
```yaml
connector.class: io.debezium.connector.postgresql.PostgresConnector
database.hostname: master.db
table.include.list: public.orders
plugin.name: pgoutput
# Master postgres → Kafka → search/analytics consumers
```

### Schema-first (protobuf)
```proto
syntax = "proto3";
message User {
  string id = 1;
  string email = 2;
  bool active = 3;
}
// codegen → TS, Go, Python types — single schema source
```

### Materialized view (Postgres)
```sql
CREATE MATERIALIZED VIEW user_stats AS
SELECT user_id, COUNT(*) AS orders, SUM(total) AS revenue
FROM orders GROUP BY user_id;

REFRESH MATERIALIZED VIEW CONCURRENTLY user_stats;
```

### SCIM provisioning
```typescript
// IdP (Okta) → /scim/v2/Users — app receives, never originates user identity
app.put('/scim/v2/Users/:id', (req, res) => {
  await db.upsertUser(req.params.id, req.body);
  res.status(200).json(req.body);
});
```

### TanStack Query cache as derived
```typescript
const { data: user } = useQuery({
  queryKey: ['user', id],
  queryFn: () => api.getUser(id),
  staleTime: 60_000,
});
// Server is SSoT — cache is derived view with TTL
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Cross-system data sync | CDC from master DB |
| Cloud config | Git + Terraform |
| User identity | IdP + SCIM |
| Frontend state | Normalized Redux + selectors |
| Analytics | Reflect master via warehouse |

**기본값**: master + derived projections — never multi-master unless conflict-resolution strategy defined.

## 🔗 Graph
- 부모: [[Data-Modeling]]
- 변형: [[Event-Sourcing]] · [[CQRS]]
- 응용: [[Redux-Toolkit]] · [[Terraform]] · [[CDC]] · [[GitOps]]
- Adjacent: [[Eventual-Consistency]]

## 🤖 LLM 활용
**언제**: design-time data flow review, drift audit, cache invalidation strategy.
**언제 X**: distributed systems with offline-first requirement — CRDT 가 적합.

## ❌ 안티패턴
- **Dual-write**: 매 app writes both DB and search — drift inevitable. CDC 사용.
- **Console drift**: cloud console change without IaC update.
- **Cached as authoritative**: TTL stale → cache mistakenly trusted.

## 🧪 검증 / 중복
- Verified (Fowler, Kleppmann DDIA, Redux docs, Terraform best practices).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — SSoT principle, master + derived patterns, CDC/IaC/SCIM |