denoland/deno · error · Error

Bad cluster.schedulingPolicy: ${schedulingPolicy}

Error message

Bad cluster.schedulingPolicy: ${schedulingPolicy}

What it means

cluster.setupPrimary() (alias setupMaster) copies cluster.schedulingPolicy into a local and requires it to be exactly SCHED_NONE or SCHED_RR, the numeric constants exported by the cluster module; anything else throws a plain Error with this message. The default derives from NODE_CLUSTER_SCHED, so an unexpected value usually means code or config assigned a string like "rr" or left the policy undefined.

Source

Thrown at ext/node/polyfills/internal/cluster/primary.ts:117

    const settings = {
      args: ArrayPrototypeSlice(process.argv, 2),
      exec: process.argv[1],
      execArgv: process.execArgv,
      silent: false,
      ...cluster.settings,
      ...options,
    };

    cluster.settings = settings;

    if (setupCalled === true) {
      return process.nextTick(setupSettingsNT, settings);
    }

    setupCalled = true;
    schedulingPolicy = cluster.schedulingPolicy;
    if (schedulingPolicy !== SCHED_NONE && schedulingPolicy !== SCHED_RR) {
      throw new Error(`Bad cluster.schedulingPolicy: ${schedulingPolicy}`);
    }

    process.nextTick(setupSettingsNT, settings);
  };
  cluster.setupMaster = cluster.setupPrimary;

  function setupSettingsNT(settings: any) {
    cluster.emit("setup", settings);
  }

  function createWorkerProcess(id: number, env: any) {
    const workerEnv: any = {
      ...(process as any).env,
      ...env,
      NODE_UNIQUE_ID: `${id}`,
    };
    if (schedulingPolicy === SCHED_RR) {
      workerEnv.NODE_CLUSTER_SCHED_POLICY = "rr";

View on GitHub (pinned to 9ad36f7a2c)

Solutions

1. Use the exported constants: cluster.SCHED_RR / cluster.SCHED_NONE
2. Validate before setup: if (p !== cluster.SCHED_RR && p !== cluster.SCHED_NONE) throw
3. Map config strings to constants in one place: "rr" -> cluster.SCHED_RR, "none" -> cluster.SCHED_NONE

Example fix

// before
cluster.schedulingPolicy = process.env.CLUSTER_SCHED; // "rr" -> throws
cluster.setupPrimary();

// after
const policy = process.env.CLUSTER_SCHED === "none"
  ? cluster.SCHED_NONE
  : cluster.SCHED_RR;
cluster.schedulingPolicy = policy;
cluster.setupPrimary();

const policy = cluster.schedulingPolicy;
if (policy !== cluster.SCHED_RR && policy !== cluster.SCHED_NONE) {
  throw new Error(`invalid schedulingPolicy: ${policy}`);
}
cluster.setupPrimary();

const isValidSchedulingPolicy = (p) => p === cluster.SCHED_RR || p === cluster.SCHED_NONE;

When it happens

Trigger: cluster.schedulingPolicy = "rr" followed by setupPrimary(); setupPrimary({ schedulingPolicy: Number(process.env.SCHED) }) where the env var is unset (NaN) or not 1/2.

Common situations: Docs or blog snippets that use string policy names; env-driven config with a typo or missing value; hard-coded numeric constants ported between versions.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• ERR_OUT_OF_RANGE
• ERR_TLS_PROTOCOL_VERSION_CONFLICT
• ERR_TLS_INVALID_PROTOCOL_VERSION
• ERR_INVALID_ARG_TYPE
• ${name} must be 'an integer' but was ${value}

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/069a64a5defe7c09. Report an issue: GitHub.