Global middleware in NestJS - Performance & Optimization

Performance: Global middleware

MEDIUM IMPACT

Global middleware affects the request processing time and overall server response speed by running on every incoming request.

Applying middleware logic to all incoming HTTP requests

NestJS

app.use((req, res, next) => {
  if (req.path.startsWith('/api')) {
    lightweightCheck();
  }
  next();
});

Runs lightweight checks only on relevant routes, reducing unnecessary processing.

📈 Performance GainReduces blocking time per request, improving INP and overall throughput.

Applying middleware logic to all incoming HTTP requests

NestJS

app.use((req, res, next) => {
  heavyComputation();
  next();
});

Runs expensive computation on every request, increasing response time and blocking event loop.

📉 Performance CostBlocks event loop for each request, increasing INP and slowing server response.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Heavy synchronous global middleware	N/A (server-side)	N/A	N/A	[X] Bad
Lightweight conditional global middleware	N/A (server-side)	N/A	N/A	[OK] Good

Rendering Pipeline

Global middleware runs early in the server request pipeline before route handlers, affecting how fast the server can start sending a response.

→Request Parsing

→Middleware Execution

→Route Handling

⚠️ BottleneckMiddleware Execution when middleware is heavy or synchronous

Core Web Vital Affected

INP

Global middleware affects the request processing time and overall server response speed by running on every incoming request.

Optimization Tips

1Keep global middleware logic minimal and asynchronous.

2Apply global middleware only to necessary routes when possible.

3Avoid heavy computations inside global middleware to prevent blocking.

Performance Quiz - 3 Questions

What is the main performance risk of using heavy global middleware in NestJS?

A It causes layout shifts in the browser.

B It increases the size of the client bundle.

C It blocks the event loop on every request, increasing response time.

D It reduces the number of HTTP requests.

DevTools: Performance (Node.js profiling tools or NestJS debug logs)

How to check: Use Node.js profiler or NestJS logging to measure middleware execution time per request.

What to look for: Look for long blocking times or high CPU usage during middleware execution indicating slow middleware.