DSM

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Service Discovery & Routing ​

This cookbook shows how to use a register collection for service discovery hints, route tables, and gateway-visible endpoint metadata.

When This Pattern Fits ​

Use this pattern when:

  • one logical key maps to one latest route value
  • reads should stay local and cheap
  • writers do not need multi-node merge semantics
  • the data is coordination metadata, not system-of-record business data

Typical examples:

  • gateway route hints
  • active upstream endpoint metadata
  • per-region ingress targets
  • collection type: REGISTER
  • locator example: shared/gateway/route-hints
  • entity type: immutable DsmEntity<E> record
  • persistence default: ephemeral

Mental Model ​

Service discovery and routing flow

Entity Model ​

java
public record RouteHint(
        String entryKey,
        EntityMetadata metadata,
        String address)
        implements DsmEntity<RouteHint> {

    @Override
    public RouteHint withMetadata(EntityMetadata metadata) {
        return new RouteHint(entryKey, metadata, address);
    }
}

Use the route name, upstream logical name, or shard key as entryKey().

Registration Pattern ​

java
DsmRegister<RouteHint> routeHints = runtime.register(
    CollectionSpecBuilder.<RouteHint>register(
            "shared",
            "gateway",
            "route-hints")
        .schemaId("route-hints/v1")
        .codec(new RouteHintCodec())
        .build());

Read/Write Pattern ​

java
routeHints.put(new RouteHint("orders", null, "10.0.0.12:8443"));

Optional<RouteHint> hint = routeHints.get("orders");
List<RouteHint> snapshot = routeHints.all();

Operational Flow ​

The operational flow is local-first: node-a puts a route hint, the local register updates, runtime metadata is stamped, steady-state replication sends the delta, and lagging peers are repaired later by replay or snapshot.

Design Rules ​

  • keep values small and routing-oriented
  • do not store large endpoint catalogs or heavy health details in DSM entities
  • prefer one route hint collection per application domain instead of one giant mixed-purpose register
  • change schemaId when route payload semantics change incompatibly

Common Mistakes ​

Using A Register For Ownership ​

If the real question is "which worker currently owns shard-17", this should be a lease collection, not a register.

Storing Primary Service Data ​

Route hints are coordination metadata. Do not treat DSM as the source of truth for customer or order data.

Overloading One Collection ​

Do not mix unrelated routing, feature flags, and operational toggles into one collection just because they are all "metadata".

Spring Boot Shape ​

yaml
dsm:
  collections:
    - bean-name: routeHintsCollection
      tenant-id: shared
      application-id: gateway
      collection-id: route-hints
      schema-id: route-hints/v1
      type: REGISTER
      consistency-tier: REGISTER
      codec-bean: routeHintCodec