Stop Optimizing Code If Your Infrastructure Is the Bottleneck

It is September 2025. If you are still running latency-critical microservices on Node.js v18 because "it works," you are hemorrhaging CPU cycles. The runtime war has shifted. Bun has matured from a chaotic disruptor to a stable, viable alternative for production workloads, specifically here in the Nordic region where latency to the end-user is scrutinized down to the millisecond.

I recently audited a middleware service for a FinTech client in Oslo. They were handling webhook ingestion with a standard Node.js Express stack. The code was clean, but the throughput was abysmal during peak trading hours. They blamed the event loop. I blamed the hardware.

We migrated the service to Bun and moved it from a generic European cloud provider to a localized CoolVDS instance with dedicated NVMe storage. The result? A 4x drop in Time to First Byte (TTFB). Here is why that happened and how you can replicate it.

The Architecture of Speed: JavaScriptCore vs. V8

Node.js runs on V8 (Google Chrome's engine). Bun runs on JavaScriptCore (Apple Safari's engine). While V8 is optimized for sustained throughput in a browser, JavaScriptCore is aggressively tuned for faster startup times and lower memory footprints. This distinction is critical for containerized environments where pods spin up and down dynamically.

However, this speed is useless if your I/O is choked. Bun's `Bun.file()` API is a direct wrapper around the `read()` syscall, bypassing much of the overhead Node.js introduces. But if that syscall hits a spinning HDD or a network-attached storage (NAS) volume competing with 500 other neighbors, the runtime advantage evaporates.

Pro Tip: Always verify your disk I/O before blaming the runtime. Run fio --name=random-write --ioengine=posixaio --rw=randwrite --bs=4k --size=4g --numjobs=1 --iodepth=1 --runtime=60 --time_based --end_fsync=1. If your IOPS are under 10k, your hosting provider is throttling you. CoolVDS NVMe instances typically benchmark significantly higher, ensuring the disk keeps up with Bun's ingestion rate.

Benchmark: The "Hello World" Lie vs. Real World I/O

Synthetics are dangerous, but they illustrate the baseline. Let's look at a simple HTTP server. In Node.js, you might use Fastify or Express. In Bun, you use the native `Bun.serve`.

1. The Native Bun Server

// index.ts
const port = 3000;
console.log(`Listening on port ${port}`);

Bun.serve({
  port,
  fetch(req) {
    const url = new URL(req.url);
    if (url.pathname === "/") return new Response("Velkommen til CoolVDS!");
    if (url.pathname === "/health") return new Response("OK");
    return new Response("404!", { status: 404 });
  },
});

To run this, you simply execute:

bun run index.ts

2. The File System BottleNeck

Real apps read files. Let's say you are serving a static config or a template. In Node, `fs.readFile` is the standard. In Bun, we map the file directly into memory.

// file-ops.ts
const file = Bun.file("heavy-data.json");

// This is lazy. It doesn't read until you await the content.
const text = await file.text();
console.log(`File size: ${file.size} bytes`);

On a shared VPS with "noisy neighbors" (CPU stealing), the context switch required to read that file can lag. Bun is multi-threaded at the engine level for I/O, but it cannot invent CPU cycles that the hypervisor has stolen from you. This is why we enforce strict KVM isolation at CoolVDS. Your cores are your cores.

Migration Strategy: Replacing npm with Bun

One of the immediate wins for DevOps teams is CI/CD pipeline speed. `bun install` is orders of magnitude faster than `npm install` because it uses a binary lockfile format and aggressive caching.

Here is a standard Dockerfile optimization we use for Norwegian clients deploying to our Oslo nodes. It leverages Bun for the build step to cut deployment time:

# Dockerfile
FROM oven/bun:1.1 as base
WORKDIR /usr/src/app

# Install dependencies into temp folder
# caching is handled by the bind mount in more complex setups
FROM base AS install
RUN mkdir -p /temp/dev
COPY package.json bun.lockb /temp/dev/
RUN cd /temp/dev && bun install --frozen-lockfile

# Copy source and prerelease
FROM base AS prerelease
COPY --from=install /temp/dev/node_modules node_modules
COPY . .

# Optimizing for production
ENV NODE_ENV=production
RUN bun test
RUN bun build ./index.ts --outdir ./out --target bun

# Final minimal image
FROM base AS release
COPY --from=prerelease /usr/src/app/out/index.js .
ENTRYPOINT [ "bun", "run", "index.js" ]

By using this multi-stage build, you strip away the bloat. Deploying this container on a CoolVDS instance ensures that the startup time remains under 200ms, which is vital for auto-scaling events.

The Compliance Angle: GDPR and Data Residency

Performance isn't just about speed; sometimes it's about legal risk. If you are using Bun to process user data (like `Bun.password.hash` for authentication), where does that data live?

Using US-based cloud giants introduces Schrems II complexity. By hosting your high-performance Bun runtime on CoolVDS, you ensure data persistence remains within Norwegian borders, satisfying Datatilsynet requirements. We peer directly at NIX (Norwegian Internet Exchange), meaning your packets often don't even leave the country to reach your Oslo-based users.

Configuring Bun for Secure Headers

Don't forget security. Bun makes it easy to add headers, but you must be explicit.

Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response("Secure Data", {
      headers: {
        "X-Content-Type-Options": "nosniff",
        "X-Frame-Options": "DENY",
        "Strict-Transport-Security": "max-age=63072000; includeSubDomains; preload"
      }
    });
  }
});

Combine this with a localized reverse proxy (Nginx or Caddy) on your VPS for SSL termination, and you have a fortress.

Conclusion: Speed Requires Foundations

Bun is an incredible tool. It solves the bloated node_modules problem and drastically reduces cold starts. But a race car engine in a golf cart frame will simply rattle itself to pieces. To truly leverage Bun's non-blocking I/O and rapid startup, you need infrastructure that guarantees low-latency disk access and zero CPU steal time.

If you are building the next generation of real-time apps for the Norwegian market, stop settling for oversold shared hosting.

Ready to test the difference? Deploy a CoolVDS NVMe instance in Oslo today and run your own `bun install` benchmark. If it's not at least 3x faster than your current provider, you are overpaying.