Custom instrumentation

To report on the performance of transactions served by your application, use the Go agentR17;s API. Instrumentation refers to modifying your application code to report a:

Transaction - A top-level operation in your application, such as an HTTP or RPC request.
Span within a transaction - An operation within a transaction, such as a database query, or a request to another service.
Error - May refer to Go errors or panics.

To report these, use a apm.Tracer̴1;R12;̴1;typically apm.DefaultTracer(), which is configured via environment variables. In the code examples below, we will refer to apm.DefaultTracer(). Please refer to the API documentation for a more thorough description of the types and methods.

Transactions

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To report a transaction, call apm.DefaultTracer().StartTransaction with the transaction name and type. This returns a Transaction object; the transaction can be customized with additional context before you call its End method to indicate that the transaction has completed. Once the transactionR17;s End method is called, it will be enqueued for sending to the Elastic APM server, and made available to the APM app.

tx := apm.DefaultTracer().StartTransaction("GET /api/v1", "request")
defer tx.End()
...
tx.Result = "HTTP 2xx"
tx.Context.SetLabel("region", "us-east-1")

The agent supports sampling transactions: non-sampled transactions will be still be reported, but with limited context and without any spans. To determine whether a transaction is sampled, use the Transaction.Sampled method; if it returns false, you should avoid unnecessary storage or processing required for setting transaction context.

Once you have started a transaction, you can include it in a context object for propagating throughout the application. See context propagation for more details.

ctx = apm.ContextWithTransaction(ctx, tx)

Spans

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To report an operation within a transaction, use Transaction.StartSpan or apm.StartSpan to start a span given a transaction or a context containing a transaction, respectively. Like a transaction, a span has a name and a type. A span can have a parent span within the same transaction. If the context provided to apm.StartSpan contains a span, then that will be considered the parent. See context propagation for more details.

span, ctx := apm.StartSpan(ctx, "SELECT FROM foo", "db.mysql.query")
defer span.End()

Transaction.StartSpan and apm.StartSpan will always return a non-nil Span, even if the transaction is nil. It is always safe to defer a call to the spanR17;s End method. If setting the spanR17;s context would incur significant overhead, you may want to check if the span is dropped first, by calling the Span.Dropped method.

Panic recovery and errors

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To recover panics and report them along with your transaction, use the Tracer.Recovered method in a recovery function. There are also methods for reporting non-panic errors: Tracer.NewError, Tracer.NewErrorLog, and apm.CaptureError.

defer func() {
	if v := recover(); v != nil {
		e := apm.DefaultTracer().Recovered()
		e.SetTransaction(tx) // or e.SetSpan(span)
		e.Send()
	}
}()

See the Error API for details and examples of the other methods.

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