51 lines
3.1 KiB
Go
51 lines
3.1 KiB
Go
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// Package tracer contains Datadog's core tracing client. It is used to trace
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// requests as they flow across web servers, databases and microservices, giving
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// developers visibility into bottlenecks and troublesome requests. To start the
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// tracer, simply call the start method along with an optional set of options.
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// By default, the trace agent is considered to be found at "localhost:8126". In a
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// setup where this would be different (let's say 127.0.0.1:1234), we could do:
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// tracer.Start(tracer.WithAgentAddr("127.0.0.1:1234"))
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// defer tracer.Stop()
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//
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// The tracing client can perform trace sampling. While the trace agent
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// already samples traces to reduce bandwidth usage, client sampling reduces
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// performance overhead. To make use of it, the package comes with a ready-to-use
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// rate sampler that can be passed to the tracer. To use it and keep only 30% of the
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// requests, one would do:
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// s := tracer.NewRateSampler(0.3)
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// tracer.Start(tracer.WithSampler(s))
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//
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// All spans created by the tracer contain a context hereby referred to as the span
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// context. Note that this is different from Go's context. The span context is used
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// to package essential information from a span, which is needed when creating child
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// spans that inherit from it. Thus, a child span is created from a span's span context.
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// The span context can originate from within the same process, but also a
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// different process or even a different machine in the case of distributed tracing.
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//
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// To make use of distributed tracing, a span's context may be injected via a carrier
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// into a transport (HTTP, RPC, etc.) to be extracted on the other end and used to
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// create spans that are direct descendants of it. A couple of carrier interfaces
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// which should cover most of the use-case scenarios are readily provided, such as
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// HTTPCarrier and TextMapCarrier. Users are free to create their own, which will work
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// with our propagation algorithm as long as they implement the TextMapReader and TextMapWriter
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// interfaces. An example alternate implementation is the MDCarrier in our gRPC integration.
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//
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// As an example, injecting a span's context into an HTTP request would look like this:
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// req, err := http.NewRequest("GET", "http://example.com", nil)
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// // ...
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// err := tracer.Inject(span.Context(), tracer.HTTPHeadersCarrier(req.Header))
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// // ...
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// http.DefaultClient.Do(req)
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// Then, on the server side, to continue the trace one would do:
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// sctx, err := tracer.Extract(tracer.HTTPHeadersCarrier(req.Header))
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// // ...
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// span := tracer.StartSpan("child.span", tracer.ChildOf(sctx))
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// In the same manner, any means can be used as a carrier to inject a context into a transport. Go's
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// context can also be used as a means to transport spans within the same process. The methods
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// StartSpanFromContext, ContextWithSpan and SpanFromContext exist for this reason.
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//
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// Some libraries and frameworks are supported out-of-the-box by using one
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// of our integrations. You can see a list of supported integrations here:
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// https://godoc.org/gopkg.in/DataDog/dd-trace-go.v1/contrib
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package tracer // import "gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer"
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