Local Provider

The reventless-local package implements all Reventless adapter interfaces using in-memory data structures. It is designed for local development and testing — no cloud infrastructure, no deployment, no costs.

Key Features

• Shared Event Bus — LocalBus provides event fan-out (PubSub) and command dispatch using Effect's PubSub and Queue primitives
• Synchronous Processing — events flow through the entire system within a single process, making tests deterministic
• Test Runner — TestRunner.setup() activates Pulumi mock mode so components can be instantiated in Jest
• Built-in GraphQL Server — starts automatically on port 4000 after all plugins are constructed
• Built-in MCP Server — provides AI-native access to commands and read models

Architecture

Unlike the AWS provider which creates separate Lambda functions connected by SQS and SNS, the Local provider runs everything in a single Node.js process:

Platform.Make()
  ├── LocalBus (shared event + command bus)
  ├── Aggregate Builders → EventLogStorage_InMemory + LocalCommandTopicChannel + ...
  ├── ReadModel Builders → QueryDbStorage_InMemory + LocalEventCollectorChannel + ...
  ├── DCB Builders → DcbEventLogStorage_InMemory + ...
  ├── GraphQL Server (port 4000)
  └── MCP Server

The bus acts as the glue: aggregates publish events to the bus, and read models subscribe to the bus for event delivery. Command handlers are registered on the bus and invoked directly.

Service Mappings

Component	Local Implementation	Data Structure
EventLog	EventLogStorage_InMemory	Dict<string, array<JSON.t>> via STM TRef
CommandTopic	LocalCommandTopicChannel	Bus command dispatch (direct handler call)
EventTopic	LocalEventTopicPublisher	Bus PubSub fan-out
EventCollector	LocalEventCollectorChannel	Bus event subscription
QueryDb	QueryDbStorage_InMemory	Dict<string, JSON.t> via STM TRef
Task	LocalTaskBucket	Dict<string, string> via STM TRef
CommandGenerator	LocalCommandGeneratorResolvers	Direct function binding
Counter	LocalCounterHandler	Dict<string, int> via STM TRef
Heartbeat	LocalHeartbeatRunner	setInterval timer
QueryEngine	LocalQueryEngine	In-memory scan + filter over QueryDb
ScheduledPublisher	LocalScheduledPublisher	setInterval timer + Bus dispatch
SideEffectHandler	LocalSideEffectHandler	Bus event subscription with handler callback
DcbEventLog	DcbEventLogStorage_InMemory	array<event> with tag-based filtering

Differences from AWS

Aspect	Local	AWS
Persistence	None — data lost on process exit	DynamoDB, S3
Event delivery	Synchronous (2-3 microtask ticks)	Asynchronous (SQS/SNS)
Concurrency	Single-threaded	Multi-Lambda concurrent execution
Infrastructure	None	Pulumi-managed AWS resources
Cost	Free	Pay-per-use AWS pricing
Ordering	Guaranteed (single process)	FIFO queues provide per-aggregate ordering

Next Steps

• Getting Started — set up and run with the Local provider
• Adapter details — how each adapter works internally