Workers - iii

How workers expand iii

Workers add capability to an iii system. Each one contributes functions and triggers the engine can route to. This page covers deploying and wiring workers into a project. Once connected, a worker exposes:

Functions, callable by function_id from anywhere in the system (see Using iii / Functions).
Triggers it advertises, which other workers can bind their functions to (see Using iii / Triggers).

For the full SDK surface each Worker can use when interacting with iii, see the complete SDK reference by language: Node, Python, Rust, or Browser.

Scaffold a new worker

iii worker init creates a new standalone worker from scratch. The command writes a language-specific project directory with the iii SDK installed, an iii.worker.yaml manifest, and example function and trigger registrations you can replace with your own.

# Interactive: prompts for the language
iii worker init my-worker

# Fully scripted: pass --language to skip the prompt
iii worker init my-worker --language typescript

Supported languages: typescript (ts), javascript (js), python (py), rust (rs). The positional NAME is the target directory; pass --directory to override it. Re-running iii worker init on a directory that already holds an iii worker (ie. has .iii/worker.ini) will make no changes to the worker. Worker init will fail by default when targeting a non-empty directory, use --allow-non-empty to scaffold into any other non-empty directory.

To install an existing worker from the registry instead of scaffolding a new one, use iii worker add. See Using iii / Workers for the registry surface.

Connecting to the engine

A worker connects to the engine over WebSocket. The convention is to set the engine URL via the III_URL environment variable, but it can also be passed explicitly to register_worker. The connection string is the only coupling between a worker and the iii instance it joins, so the worker process can be deployed anywhere reachable on the network.

Node / TypeScript
Python
Rust

import { registerWorker } from "iii-sdk";

const url = process.env.III_URL;
if (!url) throw new Error("III_URL must be set");
const worker = registerWorker(url, {
  workerName: "my-worker",
  workerDescription: "One-line summary of what this worker does",
});

import os
from iii import register_worker, InitOptions

worker = register_worker(
    os.environ.get("III_URL"),
    InitOptions(
        worker_name="my-worker",
        worker_description="One-line summary of what this worker does",
    ),
)

use iii_sdk::{InitOptions, WorkerMetadata, register_worker};

let url = std::env::var("III_URL").expect("III_URL must be set");
let worker = register_worker(
    &url,
    InitOptions {
        metadata: Some(WorkerMetadata {
            name: "my-worker".into(),
            description: Some("One-line summary of what this worker does".into()),
            ..Default::default()
        }),
        ..Default::default()
    },
);

Worker lifecycle

States

Workers transition through a small set of states after connecting: connecting → connected → available / busy → disconnected. connecting is the WebSocket handshake. connected means the Worker has joined the Engine’s registry. available and busy describe whether the Worker is currently handling invocations. disconnected is the terminal state when the WebSocket closes. The Engine tracks these transitions and surfaces them to other Workers and tooling through its discovery functions, so the rest of the system can react.

Inspecting the live registry

To see what’s currently connected to the Engine, invoke one of the engine::*::list Functions to get the current state of the registry. Each returns a list:

Function	What it returns
`engine::workers::list`	Every connected Worker with metrics.
`engine::functions::list`	Every registered Function. Filterable by `include_internal`.
`engine::triggers::list`	Every registered Trigger. Filterable by `include_internal`.
`engine::trigger-types::list`	Every advertised Trigger type with its config and call schemas.

Example: list registry contents

Node / TypeScript
Python
Rust

// engine::workers::list, pass { worker_id: "<uuid>" } to look up one worker
const { workers } = await worker.trigger({
  function_id: "engine::workers::list",
  payload: {},
});

// engine::functions::list
const { functions } = await worker.trigger({
  function_id: "engine::functions::list",
  payload: { include_internal: false },
});

// engine::triggers::list
const { triggers } = await worker.trigger({
  function_id: "engine::triggers::list",
  payload: { include_internal: false },
});

// engine::trigger-types::list
const { trigger_types } = await worker.trigger({
  function_id: "engine::trigger-types::list",
  payload: { include_internal: false },
});

# engine::workers::list, pass {"worker_id": "<uuid>"} to look up one worker
workers = worker.trigger({
    "function_id": "engine::workers::list",
    "payload": {},
})["workers"]

# engine::functions::list
functions = worker.trigger({
    "function_id": "engine::functions::list",
    "payload": {"include_internal": False},
})["functions"]

# engine::triggers::list
triggers = worker.trigger({
    "function_id": "engine::triggers::list",
    "payload": {"include_internal": False},
})["triggers"]

# engine::trigger-types::list
trigger_types = worker.trigger({
    "function_id": "engine::trigger-types::list",
    "payload": {"include_internal": False},
})["trigger_types"]

use iii_sdk::TriggerRequest;
use serde_json::json;

// engine::workers::list, pass json!({ "worker_id": "<uuid>" }) to look up one worker
let workers = worker
    .trigger(TriggerRequest {
        function_id: "engine::workers::list".into(),
        payload: json!({}),
        action: None,
        timeout_ms: None,
    })
    .await?;

// engine::functions::list
let functions = worker
    .trigger(TriggerRequest {
        function_id: "engine::functions::list".into(),
        payload: json!({ "include_internal": false }),
        action: None,
        timeout_ms: None,
    })
    .await?;

// engine::triggers::list
let triggers = worker
    .trigger(TriggerRequest {
        function_id: "engine::triggers::list".into(),
        payload: json!({ "include_internal": false }),
        action: None,
        timeout_ms: None,
    })
    .await?;

// engine::trigger-types::list
let trigger_types = worker
    .trigger(TriggerRequest {
        function_id: "engine::trigger-types::list".into(),
        payload: json!({ "include_internal": false }),
        action: None,
        timeout_ms: None,
    })
    .await?;

Handling Worker disconnects

When a Worker’s WebSocket closes, the Engine cleans up after it automatically. Its Functions and Triggers leave the live registry, and any in-flight invocations of those Functions are cancelled.

In flight requests

In flight requests will get a invocation_stopped error, catch these errors and treat them like a cancellation. Retrying will fail until the Worker that owns this function reconnects.

Example: catch `invocation_stopped`

Node / TypeScript
Python
Rust

import { IIIInvocationError } from "iii-sdk";

try {
  const result = await worker.trigger({
    function_id: "math::add",
    payload: { a: 1, b: 2 },
  });
} catch (err) {
  if (err instanceof IIIInvocationError && err.code === "invocation_stopped") {
    // Worker disconnected mid-invocation. Subscribe to `engine::functions-available`
    // (see "Subscribe to changes" below) to know when to retry.
    return;
  }
  throw err;
}

from iii import IIIInvocationError

try:
    result = worker.trigger({
        "function_id": "math::add",
        "payload": {"a": 1, "b": 2},
    })
except IIIInvocationError as err:
    if err.code == "invocation_stopped":
        # Worker disconnected mid-invocation. Subscribe to `engine::functions-available`
        # (see "Subscribe to changes" below) to know when to retry.
        return
    raise

use iii_sdk::{IIIError, TriggerRequest};
use serde_json::json;

let result = worker
    .trigger(TriggerRequest {
        function_id: "math::add".into(),
        payload: json!({ "a": 1, "b": 2 }),
        action: None,
        timeout_ms: None,
    })
    .await;

match result {
    Err(IIIError::Remote { code, .. }) if code == "invocation_stopped" => {
        // Worker disconnected mid-invocation. Subscribe to `engine::functions-available`
        // (see "Subscribe to changes" below) to know when to retry.
    }
    Err(e) => return Err(e.into()),
    Ok(value) => { /* use value */ }
}

You can register a Trigger against one of the engine’s discovery events to react to topology changes as they happen. This is particularly useful for continuing work when a Worker comes back online.

Trigger	When it fires
`engine::workers-available`	A Worker connects or disconnects.
`engine::functions-available`	A Function is registered or unregistered.

Node / TypeScript
Python
Rust

worker.registerFunction(
  "discovery::on-workers",
  async (data: { event: string; worker_id: string }) => {
    if (data.event === "worker_connected") {
      // A Worker joined the registry; its Functions are callable now.
    }
  },
);
worker.registerTrigger({
  type: "engine::workers-available",
  function_id: "discovery::on-workers",
  config: {},
});

worker.registerFunction(
  "discovery::on-functions",
  async (data: { event: string; functions: { function_id: string }[] }) => {
    // `functions` is the full snapshot after the change.
    const ids = data.functions.map((f) => f.function_id);
  },
);
worker.registerTrigger({
  type: "engine::functions-available",
  function_id: "discovery::on-functions",
  config: {},
});

async def on_workers(data: dict) -> None:
    if data["event"] == "worker_connected":
        # A Worker joined the registry; its Functions are callable now.
        pass

worker.register_function("discovery::on-workers", on_workers)
worker.register_trigger({
    "type": "engine::workers-available",
    "function_id": "discovery::on-workers",
    "config": {},
})

async def on_functions(data: dict) -> None:
    # `functions` is the full snapshot after the change.
    ids = [f["function_id"] for f in data.get("functions", [])]

worker.register_function("discovery::on-functions", on_functions)
worker.register_trigger({
    "type": "engine::functions-available",
    "function_id": "discovery::on-functions",
    "config": {},
})

use iii_sdk::{RegisterFunction, RegisterTriggerInput};
use schemars::JsonSchema;
use serde::Deserialize;
use serde_json::{Value, json};

#[derive(Deserialize, JsonSchema)]
struct WorkersAvailable { event: String, worker_id: String }

#[derive(Deserialize, JsonSchema)]
struct FunctionsAvailable { event: String, functions: Vec<Value> }

worker.register_function(RegisterFunction::new_async(
    "discovery::on-workers",
    |input: WorkersAvailable| async move {
        if input.event == "worker_connected" {
            // A Worker joined the registry; its Functions are callable now.
        }
        Ok::<_, String>(())
    },
));
worker.register_trigger(RegisterTriggerInput {
    trigger_type: "engine::workers-available".into(),
    function_id: "discovery::on-workers".into(),
    config: json!({}),
    metadata: None,
})?;

worker.register_function(RegisterFunction::new_async(
    "discovery::on-functions",
    |input: FunctionsAvailable| async move {
        // `functions` is the full snapshot after the change.
        let _count = input.functions.len();
        Ok::<_, String>(())
    },
));
worker.register_trigger(RegisterTriggerInput {
    trigger_type: "engine::functions-available".into(),
    function_id: "discovery::on-functions".into(),
    config: json!({}),
    metadata: None,
})?;

Worker manifest

iii.worker.yaml is the manifest at the worker’s root that tells iii how to install dependencies, run the worker, and pass through configuration. This applies to both the iii worker CLI commands (e.g. start, stop, restart) and to workers that iii starts automatically when they’re specified in iii’s config.yaml.

name: math-worker
description: Evaluate math expressions over iii functions.
runtime:
  # Base OCI image used as the worker rootfs. Override to pin a version.
  base_image: docker.io/iiidev/python:latest
scripts:
  install: "pip install -e ."
  start: "watchfiles 'python src/math_worker.py'"

description is an optional one-line, human/LLM-readable summary of what the worker does; the iii CLI displays it when installing or inspecting the worker. scripts.install runs once to fetch dependencies and scripts.start launches the worker. Here, watchfiles reloads it whenever you edit a source file. runtime.base_image selects the OCI image iii uses as the worker’s rootfs. The manifest is metadata about starting the Worker. Once the Worker is running iii treats them all the same. A Worker started by iii via its config.yaml, via iii worker start, or a manually run process that uses the iii SDK all behave identically with the Engine.

If a worker isn’t starting correctly then make sure to check its manifest and iii worker logs.

Shutting down a worker

Call the SDK’s shutdown to close the WebSocket cleanly. The engine removes the worker’s Functions and Triggers from the registry, fires engine::workers-available with worker_disconnected, and cancels in-flight invocations targeting them with invocation_stopped. Without shutdown, an abrupt process exit reaches the same state once the engine notices the dropped socket; graceful shutdown makes it deterministic and faster.

Node / TypeScript
Python
Rust

process.on("SIGTERM", async () => {
  await worker.shutdown();
  process.exit(0);
});

import signal

def _on_term(*_):
    worker.shutdown()
    raise SystemExit(0)

signal.signal(signal.SIGTERM, _on_term)

// Rust threads do not keep the process alive on their own; await this
// before `main` returns so the connection thread exits cleanly.
worker.shutdown_async().await;

Shutdown is useful for One-shot / ephemeral workers. Kubernetes Jobs, serverless containers, or scheduled scripts can connect like any other Worker, do their work, and shutdown() (shutdown_async().await in Rust).

​How workers expand iii

​Scaffold a new worker

​Connecting to the engine

​Worker lifecycle

​States

​Inspecting the live registry

​Handling Worker disconnects

​In flight requests

​Subscribe to changes

​Worker manifest

​Shutting down a worker

How workers expand iii

Scaffold a new worker

Connecting to the engine

Worker lifecycle

States

Inspecting the live registry

Handling Worker disconnects

In flight requests

Subscribe to changes

Worker manifest

Shutting down a worker