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backendcritical PriorityID: bun-worker-resource-ceiling-sandboxing-standard

Bun 1.2 Multi-Tenant Worker Resource Ceiling and Sandbox Isolation

Enforces deterministic memory quotas and strict execution boundaries on Bun workers to prevent multi-tenant noisy-neighbor starvation and host process out-of-memory crashes. Mandates explicit resourceLimits configuration, aggressive watchdog timeouts, and mediated host-worker IPC protocols instead of direct host system access.

Prohibited Anti-Pattern: Unconstrained Worker Allocation and Unsandboxed Execution Causing Host Process OOM and Event Loop Starvation

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---
description: Bun 1.2 Multi-Tenant Worker Resource Ceiling and Sandbox Isolation - Enforces deterministic memory quotas and strict execution boundaries on Bun workers to prevent multi-tenant noisy-neighbor starvation and host process out-of-memory crashes. Mandates explicit resourceLimits configuration, aggressive watchdog timeouts, and mediated host-worker IPC protocols instead of direct host system access.
globs: src/**/*.{ts,js}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/bun-worker-resource-ceiling-sandboxing-standard"
---

# Bun 1.2 Multi-Tenant Worker Resource Ceiling and Sandbox Isolation

> **Severity**: CRITICAL | **Category**: backend
> **Anti-Pattern Warning**: Unconstrained Worker Allocation and Unsandboxed Execution Causing Host Process OOM and Event Loop Starvation

## System Constraints
You are a Principal Engineer enforcing the Bun 1.2 Worker Resource Ceiling & Sandboxing Standard. You must mandate strict memory limits, watchdog termination timers, and restricted IPC boundaries on every micro-worker spawned within multi-tenant Bun applications. Reject any raw worker instantiation lacking resourceLimits, structured error handling, or deterministic lifecycle guarantees.

## Strict Guidelines
- Engineers MUST ALWAYS supply explicit `resourceLimits` (`maxOldGenerationSizeMb`, `maxYoungGenerationSizeMb`) when instantiating `new Worker()` for tenant workloads.
- Engineers MUST NOT allow multi-tenant worker scripts direct host filesystem or network access without host-mediated IPC authorization layers.
- Services MUST attach an aggressive watchdog termination timer (via `setTimeout` or `AbortSignal`) to every worker task, invoking `worker.terminate()` immediately upon deadline expiration.
- Services MUST monitor `worker.on('error')` and standard exit codes to handle abrupt JavaScriptCore out-of-memory termination without taking down the primary event loop.
- Code SHOULD prefer worker pools with pre-allocated, recycled worker slots over unbounded, per-request worker instantiation to avoid allocation latency spikes.
- Components NEVER execute raw eval or untrusted user scripts in workers without strict schema-validated IPC boundaries and disabled eval configurations.

## Bad vs Good Implementations
### Unbounded Worker Spawning vs. Resource-Constrained Sandbox Execution

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: The worker is initialized without resourceLimits, allowing a malicious or buggy tenant script to allocate memory uncontrollably, causing JavaScriptCore to exhaust host system RAM and crash the primary Bun process. The lack of a timeout can indefinitely stall the promise and leak the worker thread.
```typescript
import { Worker } from 'bun';

export async function executeTenantJob(tenantId: string, taskPayload: unknown) {
  // Anti-pattern: No resource limits, no execution timeout, raw host access
  const worker = new Worker(new URL('./tenant-evaluator.ts', import.meta.url).href);

  return new Promise((resolve) => {
    worker.onmessage = (event) => {
      resolve(event.data);
    };
    // Unbounded payload transmission: Worker can exhaust host RAM
    worker.postMessage({ tenantId, payload: taskPayload });
  });
}
```

#### Production Standard (Correct)
> **Standard**: Applies explicit `resourceLimits` (64MB heap ceiling, 16MB young generation) to prevent noisy-neighbor memory leakage. Enforces a 5-second watchdog timer that immediately terminates runaway worker threads, cleans up resources deterministically, and guarantees graceful error handling without terminating the primary process.
```typescript
import { Worker } from 'bun';

interface TaskResult {
  success: boolean;
  data?: unknown;
  error?: string;
}

const WORKER_TIMEOUT_MS = 5000;
const MAX_HEAP_MB = 64;

export async function executeTenantJob(tenantId: string, taskPayload: unknown): Promise<TaskResult> {
  const workerUrl = new URL('./tenant-evaluator.ts', import.meta.url).href;
  
  // Enforce deterministic heap ceilings and smol mode if applicable
  const worker = new Worker(workerUrl, {
    smol: true,
    resourceLimits: {
      maxOldGenerationSizeMb: MAX_HEAP_MB,
      maxYoungGenerationSizeMb: 16,
      codeRangeSizeMb: 16
    }
  });

  return new Promise<TaskResult>((resolve) => {
    let isSettled = false;

    const cleanup = () => {
      if (!isSettled) {
        isSettled = true;
        clearTimeout(timer);
        worker.terminate();
      }
    };

    const timer = setTimeout(() => {
      cleanup();
      resolve({ success: false, error: `Execution timed out after ${WORKER_TIMEOUT_MS}ms` });
    }, WORKER_TIMEOUT_MS);

    worker.onmessage = (event: MessageEvent<TaskResult>) => {
      cleanup();
      resolve(event.data);
    };

    worker.onerror = (event: ErrorEvent) => {
      cleanup();
      resolve({ success: false, error: event.message || 'Worker isolate memory limit exceeded' });
    };

    worker.postMessage({ tenantId, payload: taskPayload });
  });
}
```
Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

Bun Runtime Inspector
Provides low-level inspection of Bun process memory, thread pools, and active worker isolates.
Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

Bun Heap Profiler CLI
Inspects and asserts memory boundaries, active isolates, and GC heap statistics across multi-worker deployments.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Bun 1.2 Multi-Tenant Worker Resource Ceiling and Sandbox Isolation

Bun 1.2 Multi-Tenant Worker Resource Ceiling and Sandbox Isolation defines an industrial-grade behavioral standard for backend engineering. Enforces deterministic memory quotas and strict execution boundaries on Bun workers to prevent multi-tenant noisy-neighbor starvation and host process out-of-memory crashes. Mandates explicit resourceLimits configuration, aggressive watchdog timeouts, and mediated host-worker IPC protocols instead of direct host system access. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Unconstrained Worker Allocation and Unsandboxed Execution Causing Host Process OOM and Event Loop Starvation Without an explicit system instruction file, developers spend hours debugging silent failures.
Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure ModeAI Symptom (The Anti-Pattern)SeverityProduction Impact & Remedy
AI Hallucination & Deprecation DriftUnconstrained Worker Allocation and Unsandboxed Execution Causing Host Process OOM and Event Loop StarvationCritical
Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production.
Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture InconsistencyAI assistants produce mixed paradigms across files, creating fragmented codebase conventions.Medium
Increases cognitive load during code reviews and leads to maintenance debt across engineering teams.
Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.
Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

1

Engineers MUST ALWAYS supply explicit `resourceLimits` (`maxOldGenerationSizeMb`, `maxYoungGenerationSizeMb`) when instantiating `new Worker()` for tenant workloads.

Engineers MUST ALWAYS supply explicit `resourceLimits` (`maxOldGenerationSizeMb`, `maxYoungGenerationSizeMb`) when instantiating `new Worker()` for tenant workloads.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
2

Engineers MUST NOT allow multi-tenant worker scripts direct host filesystem or network access without host-mediated IPC authorization layers.

Engineers MUST NOT allow multi-tenant worker scripts direct host filesystem or network access without host-mediated IPC authorization layers.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
3

Services MUST attach an aggressive watchdog termination timer (via `setTimeout` or `AbortSignal`) to every worker task, invoking `worker.terminate()` immediately upon deadline expiration.

Services MUST attach an aggressive watchdog termination timer (via `setTimeout` or `AbortSignal`) to every worker task, invoking `worker.terminate()` immediately upon deadline expiration.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
4

Services MUST monitor `worker.on('error')` and standard exit codes to handle abrupt JavaScriptCore out-of-memory termination without taking down the primary event loop.

Services MUST monitor `worker.on('error')` and standard exit codes to handle abrupt JavaScriptCore out-of-memory termination without taking down the primary event loop.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
5

Code SHOULD prefer worker pools with pre-allocated, recycled worker slots over unbounded, per-request worker instantiation to avoid allocation latency spikes.

Code SHOULD prefer worker pools with pre-allocated, recycled worker slots over unbounded, per-request worker instantiation to avoid allocation latency spikes.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
6

Components NEVER execute raw eval or untrusted user scripts in workers without strict schema-validated IPC boundaries and disabled eval configurations.

Components NEVER execute raw eval or untrusted user scripts in workers without strict schema-validated IPC boundaries and disabled eval configurations.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Bun 1.2 Multi-Tenant Worker Resource Ceiling and Sandbox Isolation critical for AI coding assistants?

Enforces deterministic memory quotas and strict execution boundaries on Bun workers to prevent multi-tenant noisy-neighbor starvation and host process out-of-memory crashes. Mandates explicit resourceLimits configuration, aggressive watchdog timeouts, and mediated host-worker IPC protocols instead of direct host system access. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (Unconstrained Worker Allocation and Unsandboxed Execution Causing Host Process OOM and Event Loop Starvation) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

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