README.md

OpenTelemetry Tracing Enhancements in Backend Fibonacci Route Observability

This README file describes the changes made to an Express.js API server routes.js file (compared to uninstrumented routes.js) to introduce OpenTelemetry tracing capabilities.

It showcases custom instrumentation capabilities with granular control over the spans and traces created.

Added OpenTelemetry Module

const opentelemetry = require("@opentelemetry/api");
const tracer = opentelemetry.trace.getTracer("otel-node-server");

The OpenTelemetry API module was added to the code. It provides interfaces and classes necessary for implementing tracing. A tracer object was also instantiated with the name "otel-node-server". (the name is arbitrary, but should be descriptive of the service being instrumented, it also matches the name of our service so it'll show up in the observability tool as one service).

Modified fibonacci Function

The fibonacci function now accepts a second parameter, parentSpan. This allows the function to link its operations to the trace of the incoming HTTP request that invoked it.

const fibonacci = (n, parentSpan) => {

A new span is started at the beginning of the function. This span is set as the child of the passed parentSpan, and an attribute n is added to it.

const span = tracer.startSpan("fibonacci", {
  parent: parentSpan,
  attributes: { n },
});

If an error occurs (when n is not in the range 1 to 90), the status of the span is updated to reflect the error before the span is ended and the error is thrown.

if (n < 1 || n > 90) {
  span.setStatus({
    code: opentelemetry.SpanStatusCode.ERROR,
    message: "n must be 1 <= n <= 90",
  });
  span.end();
  throw new Error("n must be 1 <= n <= 90");
}

Within the calculation loop of the Fibonacci sequence, a new span is created for each number pushed to the sequence array. This span is named push sequence ${i}, where i is the current index. This span is also linked to the main Fibonacci function span, establishing a hierarchy of spans. Once the number is added to the sequence, the span is ended.

if (n > 2) {
  for (let i = 2; i < n; i++) {
    const pushSpan = tracer.startSpan(push sequence ${i}, {
      parent: span,
    });
    sequence.push(sequence[i - 1] + sequence[i - 2]);
    pushSpan.end();
  }
}

Finally, once the Fibonacci calculation is complete, the main Fibonacci span is ended.

span.end();

Modified /fibonacci/:n Route Handler

The route handler for GET /fibonacci/:n now creates a parent span for the incoming request. This span is named "GET /fibonacci/:n".

const parentSpan = tracer.startSpan("GET /fibonacci/:n");

The parentSpan is then passed to the fibonacci function when it is invoked.

const result = fibonacci(n, parentSpan);

Once the response has been sent, the parent span is ended.

parentSpan.end();

These changes allow for detailed tracing of the operations of the Fibonacci server. Each incoming request, the Fibonacci calculation, and the individual sequence number calculations now have their own spans, which are linked in a parent-child relationship, providing visibility into the operation and performance of the server.