service.name tag of OTEL default value is not set by default to process.env.OTEL_SERVICE_NAME.

[tskorupka]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

5.2.1

Plugin version

0.2.0

Node.js version

22.12.0

Operating system

Linux

Operating system version (i.e. 20.04, 11.3, 10)

alpine 3.21.2

Description

Hey,

I think this is a bug, when I am sending my otel data via grpc to new relic endpoint, instead of seeing all traces defined under service.name equal to my OTEL_SERVICE_NAME, I see them divided into mine OTEL_SERVICE_NAME and fastify service.name.

This ends up in having two different entities in my new relic dashboard, I can fix this by doing something like this.

export const fastifyOtelInstrumentation = new FastifyOtelInstrumentation({
  servername: process.env.OTEL_SERVICE_NAME,
});

I would expect this library to behave as defined in General SDK Configuration (Documentation) of OTEL.
https://opentelemetry.io/docs/languages/sdk-configuration/general/#otel_service_name

Kind Regards,
Tomasz.

Link to code that reproduces the bug

None

Expected Behavior

If I do not provide any configuration options for FastifyOtelInstrumentation, it should set servername default configuration option to environment variable OTEL_SERVICE_NAME, as a result it will create spans with service.name equal to it.

[metcoder95]

Thanks for the report! Would you like to send a PR for it?

[tskorupka]

Yeah I can do.