How to add request header values as attribute to a Span?

Question

The OTLP agent has a feature where you can add the values of request headers to a span as an attribute automatically through some configuration. How would you achieve this when using the tracing support provided by micrometer/spring boot?

The property supported by the agent is

otel.instrumentation.http.server.capture-response-headers

i'm curious if overriding getHighCardinalityKeyValues in the observation convention is the right path to go down? — Michael McFadyen
– Michael McFadyen, Commented Jul 1 at 15:30

Jonatan Ivanov · Accepted Answer · 2025-07-18 18:03:04Z

1

You can either override the ObservationConvention or write an ObservationFilter:

@Bean
ObservationFilter headerInfoFilter() {
    return context -> {
        if (context instanceof ServerRequestObservationContext serverContext) {
            String host = serverContext.getCarrier().getHeader("Host");
            context.addHighCardinalityKeyValue(KeyValue.of("host", host != null ? host : KeyValue.NONE_VALUE));
        }
        return context;
    };
}

answered Jul 18 at 18:03

Jonatan Ivanov

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1 Comment

Michael McFadyen Jul 22 at 13:19

Thanks Jonathon. Can always rely on you for a great answer.

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