Question about setting the endpoint url

[dubonzi]

Hi, I've been having some problems setting up the http exporter endpoint. The problem happens when I try to use an IP address as the endpoint.

Whenever I set my endpoint to '127.0.0.1:4318', I get the following error during tracer startup:

"msg"="parse url" "error"="parse \"127.0.0.1:4318\": first path segment in URL cannot contain colon" "input"="127.0.0.1:4318"

I traced the error to this point .

If I try to use 'http://127.0.0.1:4318' instead, the url ends up being modified by the SDK and I get an error when it tries to export traces (not on startup):

traces export: parse "http://http:%2F%2F127.0.0.1:4318/v1/traces": invalid URL escape "%2F"

Seems like the schema gets duplicated and ends up creating an invalid URL, which is happening here.

Im starting the exporter with these options:

otlptracehttp.WithEndpoint(endpoint),
otlptracehttp.WithInsecure()

Am I forgetting something?

[dmathieu]

I wonder if this is a parsing error due to using an IP address. What if you replace the IP with localhost?

[dubonzi]

Using localhost:4318 works, but http://localhost:4318/ produces the same error. In production we use an IP as endpoint, so thats why I'm testing with 127.0.0.1. Seems like the schema should be set before anything else and the url shouldn't be modified later like happens in the second case.

[dmathieu]

Using localhost:4318 works, but http://localhost:4318/ produces the same error.

You should not set the protocol when using WithEndpoint. So it's expected that http://localhost won't work.

So, I have been trying this out with the namedtracer example: https://github.com/open-telemetry/opentelemetry-go/blob/main/example/namedtracer/main.go

Replacing the stdoutexporter with otlp:

func initTracer() error {
	exp, err := otlptracehttp.New(context.Background(),
		otlptracehttp.WithEndpoint("127.0.0.1:4318"),
	)

	if err != nil {
		return fmt.Errorf("failed to initialize stdouttrace exporter: %w", err)
	}
	bsp := sdktrace.NewBatchSpanProcessor(exp)
	tp = sdktrace.NewTracerProvider(
		sdktrace.WithSampler(sdktrace.AlwaysSample()),
		sdktrace.WithSpanProcessor(bsp),
	)
	otel.SetTracerProvider(tp)
	return nil
}

And I'm not getting any parsing error, either using the HTTP exporter, or the gRPC one.
I don't have anything running on that port, so I'm getting a connection refused error, but that's expected.

[dubonzi]

Your example worked but it broke when I passed the endpoint as an environment variable OTEL_EXPORTER_OTLP_ENDPOINT=127.0.0.1:4318, can you try it like that? Apparently the variable is taking precedence over WithEndpoint in this case.

Looking at the code, the env var is parsed as an URL while in WithEndpoint the value is assigned directly as a string without the parse.

[dmathieu]

True, the environment variable requires a protocol. The following works:

OTEL_EXPORTER_OTLP_ENDPOINT=http://127.0.0.1:4318 go run main.go

This behavior matches the specification requirement though: https://github.com/open-telemetry/opentelemetry-specification/blob/102b00daef366e48d99f672f343fe78f777fd3af/specification/protocol/exporter.md?plain=1#L11

I wonder if we should do the same for WithEndpoint, so it matches the environment variable.

[dubonzi]

Humm I see, so I shouldn't use WithEndpoint while the environment variable is set. What I'm doing is using the same value from the environment variable in WithEndpoint, so I end up in a scenario where one breaks if the url has a schema, the other if it doesn't.

I wonder if we should do the same for WithEndpoint, so it matches the environment variable.

I think that would be ideal to keep the behaviour consistent.

[dmathieu]

See this issue: #3730

[dubonzi]

Thanks! I'll mark this as answered and follow the issue for updates.