Currency Service
This service provides functionality to convert amounts between different currencies.
Traces
Initializing Tracing
The OpenTelemetry SDK is initialized from main using the initTracer function
defined in tacer_common.h
void initTracer()
{
auto exporter = opentelemetry::exporter::otlp::OtlpGrpcExporterFactory::Create();
auto processor =
opentelemetry::sdk::trace::SimpleSpanProcessorFactory::Create(std::move(exporter));
std::vector<std::unique_ptr<opentelemetry::sdk::trace::SpanProcessor>> processors;
processors.push_back(std::move(processor));
std::shared_ptr<opentelemetry::sdk::trace::TracerContext> context =
opentelemetry::sdk::trace::TracerContextFactory::Create(std::move(processors));
std::shared_ptr<opentelemetry::trace::TracerProvider> provider =
opentelemetry::sdk::trace::TracerProviderFactory::Create(context);
// Set the global trace provider
opentelemetry::trace::Provider::SetTracerProvider(provider);
// set global propagator
opentelemetry::context::propagation::GlobalTextMapPropagator::SetGlobalPropagator(
opentelemetry::nostd::shared_ptr<opentelemetry::context::propagation::TextMapPropagator>(
new opentelemetry::trace::propagation::HttpTraceContext()));
}
Create new spans
New spans can be created and started using
Tracer->StartSpan("spanName", attributes, options). After a span is created
you need to start and put it into active context using
Tracer->WithActiveSpan(span). You can find an example of this in the Convert
function.
std::string span_name = "CurrencyService/Convert";
auto span =
get_tracer("currencyservice")->StartSpan(span_name,
{{SemanticConventions::kRpcSystem, "grpc"},
{SemanticConventions::kRpcService, "CurrencyService"},
{SemanticConventions::kRpcMethod, "Convert"},
{SemanticConventions::kRpcGrpcStatusCode, 0}},
options);
auto scope = get_tracer("currencyservice")->WithActiveSpan(span);
Adding attributes to spans
You can add an attribute to a span using Span->SetAttribute(key, value).
span->SetAttribute("app.currency.conversion.from", from_code);
span->SetAttribute("app.currency.conversion.to", to_code);
Add span events
Adding span events is accomplished using Span->AddEvent(name).
span->AddEvent("Conversion successful, response sent back");
Set span status
Make sure to set your span status to Ok, or Error accordingly. You can do this
using Span->SetStatus(status)
span->SetStatus(StatusCode::kOk);
Tracing context propagation
In C++ propagation is not automatically handled. You need to extract it from the
caller and inject the propagation context into subsequent spans. The
GrpcServerCarrier class defines a method to extract context from inbound gRPC
requests which is leveraged in the service call implementations.
The GrpcServerCarrier class is defined in tracer_common.h as follows:
class GrpcServerCarrier : public opentelemetry::context::propagation::TextMapCarrier
{
public:
GrpcServerCarrier(ServerContext *context) : context_(context) {}
GrpcServerCarrier() = default;
virtual opentelemetry::nostd::string_view Get(
opentelemetry::nostd::string_view key) const noexcept override
{
auto it = context_->client_metadata().find(key.data());
if (it != context_->client_metadata().end())
{
return it->second.data();
}
return "";
}
virtual void Set(opentelemetry::nostd::string_view key,
opentelemetry::nostd::string_view value) noexcept override
{
// Not required for server
}
ServerContext *context_;
};
This class is leveraged in the Convert method to extract context and create a
StartSpanOptions object to contain the right context which is used when
creating new spans.
StartSpanOptions options;
options.kind = SpanKind::kServer;
GrpcServerCarrier carrier(context);
auto prop = context::propagation::GlobalTextMapPropagator::GetGlobalPropagator();
auto current_ctx = context::RuntimeContext::GetCurrent();
auto new_context = prop->Extract(carrier, current_ctx);
options.parent = GetSpan(new_context)->GetContext();
Metrics
TBD
Logs
TBD