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Xar Hang
Xar Hang

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Why i Built BS9: A Self-Healing Process Manager for Bun

#webdev #bunjs #devops #javascript

Bun is fast. Extremely fast.

However, running Bun HTTP services in long-running production environments introduces familiar operational challenges:

  • Zero-Downtime Reloads: How do you reload workers when shipping code without dropping in-flight traffic?
  • Fault Tolerance: How do you recover cleanly if an unhandled exception or SIGKILL crashes a process?
  • Cross-Platform Daemons: How do you manage persistent daemons cleanly across Linux (systemd), macOS (launchd), and Windows?

While legacy tools like PM2 exist, they were architected around Node.js multi-process clustering paradigms and often hit friction when managing Bun native features.

Enter BS9 (Bun Sentinel 9).

⚡ What is BS9?

BS9 is an open-source process supervisor and high-availability clustering manager tailored specifically for Bun.

It is designed to be:

  • 🚀 Lightweight with near-zero overhead
  • 🔒 Secure (non-root by design)
  • 🛡️ Resilient against unexpected worker failures and memory spikes

🎯 What Makes BS9 Different?

1. Replace-First Rolling Reloads

Traditional process managers often terminate the old process before the new one is fully initialized and bound to the socket. BS9 uses a Replace-First strategy:

  1. Spawns generation g(n+1) in an isolated slot.
  2. Waits for genuine HTTP / IPC readiness checks to pass.
  3. Safely drains in-flight requests on generation g(n) with a configurable drain timeout.
  4. Decommissions the old worker only after the traffic handoff succeeds.

2. Same-Host State Hub

Need atomic locks, distributed leases with fencing tokens, or state persistence across worker restarts without setting up an external Redis cluster?

BS9 includes a built-in State Hub with:

  • Write-Ahead Logging (WAL)
  • Compare-And-Swap (CAS) primitives
  • Zero external infrastructure required

3. Built-in Chaos & Verification CLI

BS9 comes with verify-ha out of the box. You can test your application scripts against automated chaos experiments and rolling reloads:

bs9 verify-ha ./server.ts --concurrency 20
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It bombards your application with continuous HTTP traffic while simultaneously injecting rolling reloads and violent SIGKILL crashes, returning an actionable latency and availability report.

🚀 Getting Started

Installation

You can install BS9 via the verified installer script or directly with Bun:

# Via curl
curl -fsSLO https://github.com/xarhang/bs9/releases/download/v1.6.6/setup.sh
sha256sum setup.sh && bash setup.sh

# Or via package manager
bun install -g bs9
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Starting a Clustered Service 

# Start your service with all available CPU cores
bs9 start app.ts --name my-api -i max

# Check process cluster status
bs9 status

# Open the real-time terminal dashboard
bs9 monit
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🔗 Links & Resources

Give it a spin on your Bun projects! If you find it helpful, feel free to drop a star ⭐ on GitHub or leave your feedback and feature requests in the comments below.

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