Serverless with Bun

⚡ Introduction to Serverless with Bun

Serverless architecture has become a go-to solution for building highly scalable, cost-efficient applications. Combine that with the raw speed of Bun — and you've got a powerful combo! In this blog, we’ll dive into how you can run Bun-powered apps in a serverless environment, including examples with providers like Vercel, Cloudflare Workers, and custom setups using Docker.

🧠 What is Serverless Anyway?

Serverless doesn't mean "no server" — it means you don’t manage the servers. Your code runs in isolated, event-driven functions that scale automatically. No worrying about OS patches, infrastructure, or idle costs.

🛠️ Why Use Bun in Serverless?

• ⚡ Extremely fast cold starts
• 📦 Lightweight runtime
• 🚀 Faster dev-to-deploy cycle
• 🔋 First-class TypeScript support

🔗 Running Bun in Edge Functions (Cloudflare Workers)

Cloudflare Workers don't directly support Bun yet, but you can transpile Bun code into vanilla JS or use frameworks like Hono to bridge the gap.

// src/index.ts
import { Hono } from 'hono'

const app = new Hono()

app.get('/', (c) => c.text('🚀 Hello from Bun + Hono + Cloudflare!'))

export default app

# wrangler.toml
name = "bun-serverless"
compatibility_date = "2024-06-01"

Deploy with: npx wrangler deploy

🌐 Deploying Bun to Vercel Functions

Vercel currently doesn’t support Bun as a runtime, but you can build edge-ready functions using vanilla JS and deploy using Vercel’s edge runtime.

// api/index.ts
export const config = {
  runtime: 'edge',
}

export default async function handler(req: Request) {
  return new Response('🧨 Bun-style logic on Vercel edge!')
}

🐳 Docker-Based Serverless with OpenFaaS or AWS Lambda

Want full control? Use Bun inside a Docker container and deploy on platforms like OpenFaaS or AWS Lambda (via container image).

# Dockerfile
FROM oven/bun

WORKDIR /app
COPY . .
RUN bun install
CMD ["bun", "index.ts"]

Once containerized, you can push this to AWS ECR or any Docker registry and deploy it as a Lambda container function.

🧪 Example: Bun + Express-style Route in Serverless

Using elysia.js, a Bun-native web framework, you can easily wrap logic for serverless:

import { Elysia } from 'elysia'

const app = new Elysia()

app.get('/', () => 'Hello Serverless 🌍')

export default app

Then build and adapt your function for the target serverless environment. Bun's fast startup time makes it ideal for these use cases.

📦 Packaging Your Bun Function

When targeting serverless:

• 📁 Keep your entry file minimal
• 🔒 Avoid heavy dependencies or native binaries
• ⏱ Optimize cold start time by preloading as little as possible

🧑‍💻 GitHub Actions + Serverless

Automate your deployment using GitHub Actions. Here's a basic outline:

# .github/workflows/deploy.yml
name: Deploy Bun Function

on:
  push:
    branches: [ "main" ]

jobs:
  build-deploy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Setup Bun
        run: curl -fsSL https://bun.sh/install | bash
      - name: Install Deps
        run: bun install
      - name: Run Lint/Test
        run: bun test
      - name: Deploy to Serverless
        run: npx wrangler deploy  # or custom script

✅ Final Thoughts

Serverless with Bun is still maturing, but it's already promising. Whether you're deploying edge logic with Hono or building custom Docker-based microservices, Bun's startup time, performance, and DX make it a killer choice for modern serverless apps.

As the ecosystem evolves, expect tighter integrations with providers like Netlify, Vercel, and AWS. For now, smart abstractions like Hono and Elysia let you start building production-ready Bun functions — without compromise. 🚀