Trace context not propagated between MVC span and routing span (using SCG MVC + OTel Spring Starter)

[henry-jo]

Hello,

I'm using Spring cloud gateway (MVC) integrated with the OpenTelemetry spring starter for tracing.
However, a single incoming request generates two separate traces.

• io.opentelemetry.spring-webmvc-6.0 (server span)
• io.opentelemetry.spring-web-3.1 (client span)

Each has a different trace ID, so the routing span is not linked to the incoming one.

Below code is a part of the routing method.

    private fun buildServiceRoute(
       ...
    ): RouterFunction<ServerResponse> {
        val builder =
            route(serviceName)
                .before(uri(endpoint.url))
                .filter(
                    circuitBreaker { config ->
                        config
                            .setId(circuitBreakerId)
                            .setFallbackUri(fallbackUri)
                        if (!statusCodes.isNullOrEmpty()) {
                            config.setStatusCodes(statusCodes)
                        }
                    },
                )

        builder.route(predicate, http())

        return builder.build()
    }

I expected these two spans to be single trace.
Is this a known limitation or missing instrumentation for SCG MVC when using the Otel starter?
If not, what is the recommended way to propagate the trace context between the incoming request and routing span?

Environment

• Spring Boot: 3.5.6
• Spring Cloud: 2025.0.0
• OpenTelemetry Spring Boot Starter: 2.21.0
• JDK 24
• Propagators: tracecontext, baggage

Thank you!

[laurit]

Does it work with the agent? If it does I'd guess you'll need some spring cloud gateway specific instrumentation or reactor instrumentation to make it work with the spring starter.

[henry-jo]

@laurit
Hi, With the Java agent, I get a single trace per incoming request. (server span and routing client span are linked correctly)

However, using the Otel spring starter only (I'm on SCG MVC, no Reactor involved) and when routing via a custom RouterFunction<ServerResponse>, the routing span(= client span) starts a new trace.

Is MVC function routing(RouterFunction) currently not covered by the starter's instrumentation?
Do I need a specific instrumentation module to keep the client span as a child of the inbound server span?

[laurit]

Do I need a specific instrumentation module to keep the client span as a child of the inbound server span?

If it doesn't work out of the box it is likely that an instrumentation that is present in the agent is missing from the starter. Unfortunately it is not possible to tell what might be missing without reproducing the issue. If you wish for someone to take a look then please provide a minimal application that reproduces the issue along with any necessary instructions.