Payment Service

This service is responsible to process credit card payments for orders. It will return an error if the credit card is invalid or the payment cannot be processed.

Payment service source

Zero-code instrumentation

This Node.js based service makes use of the OpenTelemetry Node.js Zero-code Instrumentation, setting up by requiring the @opentelemetry/auto-instrumentations-node/register module at startup. Export endpoints, resource attributes, and service name are automatically set based on environment variables. This can be done in the service’s package.json start script or via NODE_OPTIONS.

"scripts": {
  "start": "node --require @opentelemetry/auto-instrumentations-node/register index.js"
}

Traces

Add attributes to auto-instrumented spans

Within the execution of auto-instrumented code you can get current span from context.

const span = opentelemetry.trace.getActiveSpan();

Adding attributes to a span is accomplished using setAttributes on the span object. In the chargeServiceHandler function an attributes is added to the span as an anonymous object (map) for the attribute key/values pair.

span?.setAttributes({
  'demo.payment.amount': parseFloat(`${amount.units}.${amount.nanos}`).toFixed(
    2,
  ),
});

Span Exceptions and status

You can use the span object’s recordException function to create a span event with the full stack trace of a handled error. When recording an exception also be sure to set the span’s status accordingly. You can see this in the charge function in charge.js.

span.recordException(err);
span.setStatus({ code: SpanStatusCode.ERROR, message: err.message });

Metrics

Creating Meters and Instruments

Meters can be created using the @opentelemetry/api package. You can create meters as seen below, and then use the created meter to create instruments.

const { metrics } = require('@opentelemetry/api');

const meter = metrics.getMeter('payment');
const transactionsCounter = meter.createCounter('demo.payment.transactions');

Meters and Instruments are supposed to stick around. This means you should get a Meter or an Instrument once , and then re-use it as needed, if possible.

Logs

TBD

Baggage

OpenTelemetry Baggage is leveraged in this service to check if the request is synthetic (from the load generator). Synthetic requests will not be charged, which is indicated with a span attribute. The charge.js file which does the actual payment processing, has logic to check the baggage.

// check baggage for synthetic_request=true, and add charged attribute accordingly
const baggage = propagation.getBaggage(context.active());
if (
  baggage &&
  baggage.getEntry('synthetic_request') &&
  baggage.getEntry('synthetic_request').value === 'true'
) {
  span.setAttribute('demo.payment.charged', false);
} else {
  span.setAttribute('demo.payment.charged', true);
}