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nicomedina
nicomedina

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How I built a high-performance Social API with Bun & ElysiaJS on a $5 VPS (handling 3.6k reqs/min)

#bunjs #api #javascript #programming

The Goal

I wanted to build a "Micro-Social" API—a backend service capable of handling Twitter-like feeds, follows, and likes—without breaking the bank. My constraints were simple:

  • Budget:** $5 - $20 / month.
  • Performance:** Sub-300ms latency.
  • Scale:** Must handle concurrent load (stress testing). Most tutorials show you Hello World. This post shows you what happens when you actually hit Hello World with 25 concurrent users on a cheap VPS. (Spoiler: It crashes). Here is how I fixed it. ## The Stack 🛠️ I chose Bun over Node.js for its startup speed and built-in tooling.
  • Runtime: Bun
  • Framework: ElysiaJS (Fastest Bun framework)
  • Database: PostgreSQL (via Dokploy)
  • ORM: Drizzle (Lightweight & Type-safe)
  • Hosting: VPS with Dokploy (Docker Compose)

The "Oh Sh*t" Moment 🚨

I deployed my first version. It worked fine for me.
Then I ran a load test using k6 to simulate 25 virtual users browsing various feeds.

k6 run tests/stress-test.js
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Result:

✗ http_req_failed................: 86.44%
✗ status is 429..................: 86.44%
The server wasn't crashing, but it was rejecting almost everyone.

Diagnosis

I initially blamed Traefik (the reverse proxy). But digging into the code, I found the culprit was me.

// src/index.ts
// OLD CONFIGURATION
.use(rateLimit({
  duration: 60_000, 
  max: 100 // 💀 100 requests per minute... GLOBAL per IP?
}))
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Since my stress test (and likely any future NATed corporate office) sent all requests from a single IP, I was essentially DDOSing myself.

The Fixes 🔧

1. Tuning the Rate Limiter

I bumped the limit to 2,500 req/min. This prevents abuse while allowing heavy legitimate traffic (or load balancers).

// src/index.ts
.use(rateLimit({
  duration: 60_000, 
  max: 2500 // Much better for standard reliable APIs
}))
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2. Database Connection Pooling

The default Postgres pool size is often small (e.g., 10 or 20).
My VPS has 4GB RAM. PostgreSQL needs RAM for connections, but not that much.
I bumped the pool to 80 connections.

// src/db/index.ts
const client = postgres(process.env.DATABASE_URL, { 
    max: 80 
});
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3. Horizontal Scaling with Docker

Node/Bun is single-threaded. A single container uses 1 CPU core effectivey.
My VPS has 2 vCPUs.
I added a replicas instruction to my docker-compose.dokploy.yml:

  api:
    build: .
    restart: always
    deploy:
      replicas: 2 # One for each core!
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This instantly doubled my throughput capacity. Traefik automatically load-balances between the two containers.

The Final Result 🟢

Ran k6 again:

  ✓ checks_succeeded...: 100.00%
  ✓ http_req_duration..: p(95)=200.45ms
  ✓ http_req_failed....: 0.00% (excluding auth checks)
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0 errors. 200ms latency. On a cheap VPS.

Takeaway

You don't need Kubernetes for a side project. You just need to understand where your bottlenecks are:

  1. Application Layer: Check your Rate Limits.
  2. Database Layer: Check your Connection Pool.
  3. Hardware: Use all your cores (Replicas). If you want to try the API, I published it on RapidAPI as Micro-Social API. https://rapidapi.com/ismamed4/api/micro-social

Happy coding! 🚀

Top comments (1)

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olivia-john profile image
Olivia John •

Great article!