quoteservice.md

Quote Service

This service is responsible for calculating shipping costs, based on the number of items to be shipped. The quote service is called from Shipping Service via HTTP.

The Quote Service is implemented using the Slim framework and php-di for managing the Dependency Injection.

The PHP instrumentation may vary when using a different framework.

Quote service source

Traces

Initializing Tracing

The OpenTelemetry SDK is initialized from index.

    $tracerProvider = (new TracerProviderFactory('quoteservice'))->create();
    ShutdownHandler::register([$tracerProvider, 'shutdown']);
    $tracer = $tracerProvider->getTracer('io.opentelemetry.contrib.php');

    $containerBuilder->addDefinitions([
        Tracer::class => $tracer
    ]);

You should call $tracerProvider->shutdown() when your service is shutdown to ensure all spans are exported.

Adding HTTP instrumentation

This service receives HTTP requests, which are instrumented in the middleware.

The middleware starts root span based on route pattern, sets span status from http code.

    $app->add(function (Request $request, RequestHandler $handler) use ($tracer) {
        $parent = TraceContextPropagator::getInstance()->extract($request->getHeaders());
        $routeContext = RouteContext::fromRequest($request);
        $route = $routeContext->getRoute();
        $root = $tracer->spanBuilder($route->getPattern())
            ->setStartTimestamp((int) ($request->getServerParams()['REQUEST_TIME_FLOAT'] * 1e9))
            ->setParent($parent)
            ->setSpanKind(SpanKind::KIND_SERVER)
            ->startSpan();
        $scope = $root->activate();

        try {
            $response = $handler->handle($request);
            $root->setStatus($response->getStatusCode() < 500 ? StatusCode::STATUS_OK : StatusCode::STATUS_ERROR);
        } finally {
            $root->end();
            $scope->detach();
        }

        return $response;
    });

This is enough to get a new span every time a new request is received by the service.

Note that the root span is created with setParent($parent) which is coming from the request headers. This is required to ensure Context Propagation.

Add span attributes

Within the definition of routes, you can get current span using OpenTelemetry\API\Trace\AbstractSpan.

    $span = AbstractSpan::getCurrent();

Adding attributes to a span is accomplished using setAttribute on the span object. In the calculateQuote function 2 attributes are added to the childSpan.

    $childSpan->setAttribute('app.quote.items.count', $numberOfItems);
    $childSpan->setAttribute('app.quote.cost.total', $quote);

Add span events

Adding span events is accomplished using addEvent on the span object. In the getquote route span events are added. Some events have additional attributes, others do not.

Adding a span event without attributes:

    $span->addEvent('Received get quote request, processing it');

Adding a span event with additional attributes:

    $span->addEvent('Quote processed, response sent back', [
        'app.quote.cost.total' => $payload
    ]);

Metrics

TBD

Logs

TBD