Fix Payment Gateway Propagation

In this step, you’ll edit application code in the payment gateway proxy so it forwards W3C Trace Context to payment-api then rebuild and redeploy the service.

In Splunk APM you’ll see this behaviour:

• frontend-api → payment-gateway - connected
• payment-gateway → payment-api - disconnected

The payment gateway still creates its own spans (so it shows in the service map), but the upstream call starts a new trace on payment-api. This mirrors real teams who add a custom BFF/proxy and forget to propagate context on outbound HTTP calls - or when code uses suppressTracing() trying to avoid “double spans” which accidentally breaks propagation.

The Fix #

Open the server.js file and locate buildUpstreamHeaders().

cd ~/workshop/context-propagation
vi services/payment-gateway/server.js

Inject W3C trace context into upstream headers #

1. Uncomment/add propagation.inject() before the return:
2. Remove suppressTracing on the upstream fetch

function buildUpstreamHeaders() {
  const headers = {
    'Content-Type': 'application/json',
  };
  return headers;
}

const upstreamContext = suppressTracing(context.active());

function buildUpstreamHeaders() {
  const headers = {
    'Content-Type': 'application/json',
  };

  propagation.inject(context.active(), headers, {
    set: (carrier, key, value) => {
      carrier[key] = value;
    },
  });

  return headers;
}

const upstreamContext = context.active();

cp ./services/payment-gateway/server-fixed.js ./services/payment-gateway/server.js

diff ./services/payment-gateway/server.js ./services/payment-gateway/server-fixed.js