Auto configuration of the java agent and adding custom pass through propagator

[grahamia]

I am trying to propagate custom headers in a application using the PassThroughPropagator (following the changes made here - typelevel/otel4s#277).

I had it all working by instanciating the otel instance within code, i.e.

AutoConfiguredOpenTelemetrySdk
        .builder()
        .addPropagatorCustomizer { (autoConfigured, _) =>
          TextMapPropagator.composite(autoConfigured,
                                      PassThroughPropagator.create(propagationConfig.ciHeaders.map(_.toString).asJava))
        }
...

But then when trying to enable java agent to get jvm metrics etc I obviously ran into issue of agent starting the global instance and then the code also starting it, even with setting global to false still run into issue of multiple prometheus servers starting (yes, want prometheus exporter).

So after a lot of digging came across ConfigurablePropagatorProvider but then had to struggle to get that working in a otel.javaagent.extensions as the jars provided here seem to have to be self container and I assume since PassThroughPropagator is in incubator it isn't within the javaagent jar I had to go down the path of creating a fat jar containing my simple PassThroughConfigurablePropagator and include the opentelemetry-extension-incubator. Then in code just do a simple GlobalOpenTelemetry.get to obtain a handle to the global otel instance.

Is there any plan on providing a PassThroughConfigurablePropagator like other propagators that can be created through config?

My simple code is as follows:

class PassThroughConfigurablePropagator implements ConfigurablePropagatorProvider {

    @Override
    public TextMapPropagator getPropagator(ConfigProperties config) {
        return PassThroughPropagator.create(config.getList("otel.passthrough.headers"));
    }

    @Override
    public String getName() {
        return "passthrough";
    }
}

The above can then be used by adding passthrough to the env var list OTEL_PROPAGATORS and defining a list of headers in new env var OTEL_PASSTHROUGH_HEADERS

[trask]

hi @grahamia! we'd probably want to see open-telemetry/opentelemetry-specification#1717 make it into the specification, and the name defined in the specification under OTEL_PROPAGATORS before adding support for it in the out-of-the-box Java agent

[grahamia]

Thanks @trask glad I wasn't incorrect in how I got round the issues, will use what I have implemented and hopefully in the future the implementation within OpenTelemetry isnt a million miles different.