# Data Flow

## Primary Flows

| Flow | Source | Destination | Notes |
|---|---|---|---|
| Web persistence | Routes/services/stores | PostgreSQL adapter -> RDS | Parameterized SQL; related statements share one Pool client transaction. |
| Worker processing | Worker process | Internal Web Service `/api/internal/worker/tick` | Authenticated by internal token; Worker has no RDS credentials. |
| Schema rollout | ACK migration Job | RDS PostgreSQL | Versioned checksummed migrations under an advisory lock. |
| Readiness | ACK probe | Web `/api/ready` -> RDS | Verifies connection, 11 runtime tables, required privileges, and 2 functions. |

## State Ownership

- Production relational state belongs to RDS PostgreSQL when `ZHINIAN_DATA_BACKEND=postgres`.
- Local JSON under the runtime directory is an explicit development/test backend, not a production fallback.
- Uploads/generated files remain runtime/object-storage state and are not made shared by the PostgreSQL migration.

## External Interfaces

- Alibaba Cloud RDS PostgreSQL via its internal endpoint and verified TLS CA.
- Alibaba Cloud ACK resources under `deploy/ack/`.
- Internal Worker HTTP endpoint is cluster-internal and blocked from public Ingress routing.

## Last Updated

2026-08-12