How to pass opentracing data using json

Question

My API-gateway starts a tracer and a span for validate email. Then its passed to user-service for validation.

I want to pass this span details to user-service as a json object and start another span as a

tracer.start_span('Validate Email', child_of=API_gateway_span)

To do it, I have used following struct:

type checkEmail struct {
    GatewayTracerSpan opentracing.SpanContext `json: gatewayTracerSpan`
    Email             string                  `json: email`
    Uuid              string                  `json: uuid`
}

In function()

validateEmailSpan := apitracer.tracer.StartSpan("Validate Email")

emailJson := checkEmail{
            GatewayTracerSpan: validateEmailSpan.Context(),
            Email:             email,
            Uuid:              uuid,
        }

But always GatewayTracerSpan is empty value. I have just started distributed-tracing. Here I selected to use json over native http-headers as its easy for upgrade any protocol change.

Is this possible? If so, am I doing it right? Or what mistakes did I make?

Answer 1

One way to link spans from different services is to use uber-trace-id from the parent span. If you have LogSpans set to true in your ReporterConfig, uber-trace-id is what gets printed out ("Reporting span xxx-xxx-xxx").

Here is how it might look like in the code:

//API Gateway
carrier := opentracing.TextMapCarrier{} //you can use any type of carrier or even create your own
ctx, _ := opentracing.GlobalTracer().Extract(opentracing.TextMap, carrier)
span := apitracer.tracer.StartSpan(name, ext.RPCServerOption(ctx))
_ := span.Tracer().Inject(span.Context(), opentracing.TextMap, carrier)
uberTraceID := carrier["uber-trace-id"]

You can now pass uberTraceID instead of validateEmailSpan.Context() to your other services.

You can use this function in your other services:

//Email service
func NewChildSpanThatFollows(name, uberTraceID string) opentracing.Span {
    carrier := opentracing.TextMapCarrier{}
    carrier.Set("uber-trace-id", uberTraceID)
    ctx, _ := opentracing.GlobalTracer().Extract(opentracing.TextMap, carrier)
    span := opentracing.StartSpan(name, opentracing.FollowsFrom(ctx))
    _ := span.Tracer().Inject(span.Context(), opentracing.TextMap, carrier)

    return span
}

This works for me if I need to see spans between services linked together in a parent-child manner. If other information needs to be passed as well, I would suggest passing it as regular data in the JSON object, then either create my own Carrier or use tags if needed to do a search with that passed data.

span.SetTag("request_id", requestID)

EDIT:

Here you can find a great tutorial on using opentracing. It uses HTTPHeadersCarrier, it has a step by step walkthrough, but it's basically the same process as above.