OpenTracing API for Go
This package is a Go platform API for OpenTracing.
Required Reading
In order to understand the Go platform API, one must first be familiar with the OpenTracing project and terminology more specifically.
API overview for those adding instrumentation
Everyday consumers of this opentracing package really only need to worry
about a couple of key abstractions: the StartSpan function, the Span
interface, and binding a Tracer at main()-time. Here are code snippets
demonstrating some important use cases.
Singleton initialization
The simplest starting point is ./default_tracer.go. As early as possible, call
import "github.com/opentracing/opentracing-go"
import ".../some_tracing_impl"
func main() {
opentracing.SetGlobalTracer(
// tracing impl specific:
some_tracing_impl.New(...),
)
...
}Non-Singleton initialization
If you prefer direct control to singletons, manage ownership of the
opentracing.Tracer implementation explicitly.
Creating a Span given an existing Go context.Context
If you use context.Context in your application, OpenTracing's Go library will
happily rely on it for Span propagation. To start a new (blocking child)
Span, you can use StartSpanFromContext.
func xyz(ctx context.Context, ...) {
...
span, ctx := opentracing.StartSpanFromContext(ctx, "operation_name")
defer span.Finish()
span.LogFields(
log.String("event", "soft error"),
log.String("type", "cache timeout"),
log.Int("waited.millis", 1500))
...
}Starting an empty trace by creating a "root span"
It's always possible to create a "root" Span with no parent or other causal
reference.
func xyz() {
...
sp := opentracing.StartSpan("operation_name")
defer sp.Finish()
...
}Creating a (child) Span given an existing (parent) Span
func xyz(parentSpan opentracing.Span, ...) {
...
sp := opentracing.StartSpan(
"operation_name",
opentracing.ChildOf(parentSpan.Context()))
defer sp.Finish()
...
}Serializing to the wire
func makeSomeRequest(ctx context.Context) ... {
if span := opentracing.SpanFromContext(ctx); span != nil {
httpClient := &http.Client{}
httpReq, _ := http.NewRequest("GET", "http://myservice/", nil)
// Transmit the span's TraceContext as HTTP headers on our
// outbound request.
opentracing.GlobalTracer().Inject(
span.Context(),
opentracing.HTTPHeaders,
opentracing.HTTPHeadersCarrier(httpReq.Header))
resp, err := httpClient.Do(httpReq)
...
}
...
}Deserializing from the wire
http.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
var serverSpan opentracing.Span
appSpecificOperationName := ...
wireContext, err := opentracing.GlobalTracer().Extract(
opentracing.HTTPHeaders,
opentracing.HTTPHeadersCarrier(req.Header))
if err != nil {
// Optionally record something about err here
}
// Create the span referring to the RPC client if available.
// If wireContext == nil, a root span will be created.
serverSpan = opentracing.StartSpan(
appSpecificOperationName,
ext.RPCServerOption(wireContext))
defer serverSpan.Finish()
ctx := opentracing.ContextWithSpan(context.Background(), serverSpan)
...
}Conditionally capture a field using log.Noop
In some situations, you may want to dynamically decide whether or not to log a field. For example, you may want to capture additional data, such as a customer ID, in non-production environments:
func Customer(order *Order) log.Field {
if os.Getenv("ENVIRONMENT") == "dev" {
return log.String("customer", order.Customer.ID)
}
return log.Noop()
}Goroutine-safety
The entire public API is goroutine-safe and does not require external synchronization.
API pointers for those implementing a tracing system
Tracing system implementors may be able to reuse or copy-paste-modify the basictracer package, found here. In particular, see basictracer.New(...).
API compatibility
For the time being, "mild" backwards-incompatible changes may be made without changing the major version number. As OpenTracing and opentracing-go mature, backwards compatibility will become more of a priority.
Tracer test suite
A test suite is available in the harness package that can assist Tracer implementors to assert that their Tracer is working correctly.