Observability

Kaelum provides built-in middleware for common observability needs, making it easier to trace requests across microservices and measure performance metrics without adding external dependencies.

Request ID

The Request ID middleware automatically attaches a unique X-Request-Id header (using standard UUID v4) to every incoming request and outgoing response.

This is essential for:

• Tracing a single request’s lifecycle across multiple services
• Correlating log entries (by logging req.id)
• Error tracking

const kaelum = require('kaelum');
const app = kaelum();

// Enable request IDs for all requests
app.requestId();

app.get('/', (req, res) => {
  console.log(`Processing request: ${req.id}`);
  res.send('Hello World');
});

If an upstream proxy, load balancer, or API Gateway already provides an X-Request-Id header, Kaelum automatically detects and preserves it, ensuring continuous distributed tracing.

See app.requestId() API Reference for options like custom header names or generators.

Server Timing

The Timing middleware injects a Server-Timing header into the response, following the official W3C Server-Timing Specification.

This header records the exact total processing duration of the request in milliseconds and allows browsers’ developer tools (Network tab) to display backend timing metrics natively.

// Enable server timing metrics
app.timing();

The header format looks like:

Server-Timing: total;dur=12.34

See app.timing() API Reference for configuration options.