paymentservice.md

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 can not be processed.

Payment service source

Initializing OpenTelemetry

It is recommended to use a Node required module when starting your NodeJS application to initialize the SDK and auto-instrumentation. When initializing the OpenTelemetry NodeJS SDK, you optionally specify which auto-instrumentation libraries to leverage, or make use of the getNodeAutoInstrumentations() function which includes most popular frameworks. The tracing.js contains all code required to initialize the SDK and auto-instrumentation based on standard OpenTelemetry environment variables for OTLP export, resource attributes, and service name.

const opentelemetry = require("@opentelemetry/sdk-node")
const { getNodeAutoInstrumentations } = require("@opentelemetry/auto-instrumentations-node")
const { OTLPTraceExporter } =  require('@opentelemetry/exporter-trace-otlp-grpc')

const sdk = new opentelemetry.NodeSDK({
  traceExporter: new OTLPTraceExporter(),
  instrumentations: [ getNodeAutoInstrumentations() ]
})

sdk.start()

Node required modules are loaded using the --require command line argument. This can be done in the ENTRYPOINT command for the service's Dockerfile.

ENTRYPOINT [ "node", "--require", "./tracing.js", "./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({
      'app.payment.amount': parseFloat(`${amount.units}.${amount.nanos}`)
    })

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 chargeServiceHandler function

    span.recordException(err)
    span.setStatus({ code: opentelemetry.SpanStatusCode.ERROR })

Metrics

TBD

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('app.payment.charged', false);
  } else {
    span.setAttribute('app.payment.charged', true);
  }