Arc 1 Recap — Make Shared State Visible (Chapters 1–4)
Arc 1 moves from business responsibility boundaries to two-node visibility. Concurrent conflict, repair, and production networking remain for later arcs.
Understanding established in this arc
- Chapter 1 keeps orders, payments, and event history in their authoritative systems and assigns only repairable coordination state to DSM.
- Chapter 2 establishes Runtime lifecycle and limits successful
putto local commit. - Chapter 3 defines stable identity through locator, entry key, entity, metadata, codec, and schema.
- Chapter 4 observes online delta and eventual visibility on node B.
Verifiable learning outcomes
- Decide whether state can be repaired from peers or rebuilt from an authority.
- Build and close a single-node Runtime with a registered collection.
- Choose a stable key and explicit schema for
RouteHint. - Prove controlled two-node propagation with a condition and
REMOTE_DELTA.
How this arc realizes DSM's value
Arc 1 turns “shared state” into inspectable responsibility boundaries, stable identity, Runtime lifecycle, and remote visibility. Services reuse registration, encoding, and basic propagation while retaining responsibility for state suitability and the point at which remote results become safe to depend on.
Four distinct moments
| Moment | Proven | Not proven |
|---|---|---|
runtime.start() returns |
Local Runtime entered its operational lifecycle | Peer discovery or collection synchronization |
register.put() returns |
Local node accepted the change | Any remote node applied it |
Node B get() hits |
B currently sees the value | Every node agrees or no future conflict |
| Two-node test passes | Fixed source satisfies assertions under fake membership | Real networking, production capacity, or fault repair |
Common errors
| Error | Correction |
|---|---|
| Treat DSM as a transactional database | Reclassify from irreversible commitments and audit responsibility |
| Use a new entry key for every publication | Use stable business identity so Register updates one logical entry |
Verify replication with sleep |
Wait for the target condition with an explicit timeout |
| Treat a green test as production readiness | Record topology, transport, and uncovered boundaries |
Transfer exercise
Design a temporary feature flag twice. In the first design, an authoritative configuration service exists and DSM stores a rebuildable hint. In the second, no authority exists and the flag directly controls a monetary action. Explain why the first may fit DSM and the second needs stronger fact and audit guarantees.
Next
Continue to Arc 2, where Register, Lease, and CRDT address current value, ownership, and mergeable updates.