Workers

Built-in and external workers in iii.

Workers are the units that add capability to a iii system.

Worker types

Type	Examples	Description
Built-in workers	iii-http, iii-queue, iii-state, iii-stream, iii-cron, iii-observability	Rust workers shipped with the engine and enabled in config.yaml.
External workers	Node.js, Python, Rust, browser workers	SDK processes that connect to the engine and register application functions.
Managed workers	Local directories or OCI images added with iii worker add	Workers started and supervised by the iii worker manager.

Configuration

Built-in and managed workers are configured under the workers key:

workers:
  - name: iii-http
    config:
      port: 3111

  - name: iii-queue

External SDK workers usually configure only their engine address:

const iii = registerWorker(process.env.III_URL ?? 'ws://localhost:49134')

Older docs and configs may use “module” for built-in workers. In current iii, “worker” is the canonical term.

Workers are the interface between the Engine and the rest of the application. They are responsible for establishing connections to services, implementing trigger types, and supplying application Context.

Every capability in iii (HTTP endpoints, cron scheduling, state management, queues, streams, observability) is implemented as a Worker. This modular architecture means the Engine itself stays small and focused on orchestration, while Workers handle all external concerns.

Built-in Workers

Worker	Provides	Config key
HTTP	HTTP trigger type, request/response handling	rest_api
Queue	Async message processing with retries	queue
Cron	Scheduled task execution	cron
State	Key-value state storage with atomic updates	state
Stream	Real-time data streams with WebSocket push	stream
PubSub	Publish/subscribe messaging	pubsub
Observability	Structured logging, tracing, and metrics	observability
Exec	Shell command execution	exec
Bridge	WebSocket bridge for SDK connections	bridge

How Workers Work

A Worker has two responsibilities:

1. Register trigger types: A Worker can introduce new ways to invoke Functions. For example, the HTTP worker registers the http trigger type, and the Cron worker registers the cron trigger type.

2. Supply Context: A Worker can add capabilities to the Context object that gets passed to every Function. For example, the State worker adds state::get, state::set, and other state operations.

Workers are configured in config.yaml (the engine default). Use -c iii-config.yaml to specify a custom path:

workers:
  - name: iii-http
    config:
      port: 3111
      host: 0.0.0.0
  - name: iii-state
    config:
      adapter:
        name: kv
        config:
          store_method: in_memory
  - name: iii-queue
    config:
      adapter:
        name: builtin
        config:
          store_method: in_memory

You can build your own Workers to integrate any service or infrastructure. See Custom Workers for a detailed guide.