Engine

The engine is the router

The engine receives function calls, routes them to connected workers, and routes results back to callers. Project workers have their own lifecycle under Compose; config.yaml is not a general process manager.

Engine configuration

The engine reads config.yaml from the project root. Pass --config <path> to select another file. When the file is missing, interactive sessions offer to create it and non-interactive sessions create an empty one automatically.

iii --config config.yaml

Only workers coupled to the engine lifecycle may be declared in this file:

configuration
iii-worker-manager
iii-http-functions
iii-stream
iii-sandbox

The engine injects iii-engine-functions, iii-telemetry, and iii-observability automatically; do not declare them. Any other name makes initial startup or config reload fail with UNSUPPORTED_CONFIG_WORKERS and a link to the manual migration guide.

workers:
  - name: iii-stream
    config:
      port: ${STREAM_PORT:3112}
      host: 127.0.0.1
      adapter:
        name: kv
        config:
          store_method: file_based
          file_path: ./data/stream_store

  - name: configuration
    config:
      adapter:
        name: fs
        config:
          directory: ./config

The engine watches this file. A valid change reloads the affected engine worker; an invalid change stops the engine so it cannot continue with a configuration different from the file on disk.

Project workers

HTTP, cron, queue, state, pubsub, bridge, application workers, and other registry workers belong in worker-compose.yaml. For the normal managed lifecycle, move the five engine configs into its direct engine.workers map and start the single file:

iii compose --namespace dev --up --file worker-compose.yaml

Keep the list-shaped config.yaml only when another supervisor owns the engine. In that case omit engine: from the Compose file, run the processes separately, and connect with --engine <ws-url> or III_URL. See Workers for Compose lifecycle operations and Move workers from config.yaml to Compose for existing projects.

Environment variable expansion

Values in direct config.yaml and engine.workers support ${VAR:default}; the engine expands them before typing the generated YAML. Compose-owned fields such as engine.url use ${VAR:-default}. config_override is likewise carried to the configuration worker without Compose expanding it.

Default configuration

The generated file contains workers: []. Mandatory engine services still start, but no project worker does. Add project workers to worker-compose.yaml and use iii compose --up; do not add them to the empty engine list. Workers may also be started by another supervisor or on another machine. Any SDK process that connects and registers is a worker, independent of Compose.

Getting Started

Upgrading

Using iii

Understanding iii

Creating Workers

The engine is the router

Engine configuration

Project workers

Environment variable expansion

Default configuration

​The engine is the router

​Engine configuration

​Project workers

​Environment variable expansion

​Default configuration

The engine is the router

Engine configuration

Project workers

Environment variable expansion

Default configuration