Spring Boot tracing across RestClient: construct the client from Boot's builder

Keep the trace chain

The parcel API calls the rate service after accepting a request. Spring Boot instruments clients created from its auto-configured RestClient.Builder; creating a separate RestClient from scratch can omit propagation interceptors. The downstream service then logs a different trace ID, making one operation look like two. Request-factory selection and timeouts still apply to the same client; tracing is not a replacement for a deadline.

Avoid trusting client-supplied trace claims

Trace headers help correlate work; they are not authentication or authorization data. A malicious caller can supply a trace ID, so keep tenant and identity checks in the security boundary. Do not place tokens or parcel addresses in span attributes. Instrument a stable operation name and bounded low-cardinality tags.

Follow one request

Call the parcel API, let it call the rate service, and compare trace IDs and parent-child spans in the collector. Repeat with the client created outside the managed builder to demonstrate the gap. This bean is only a client-construction sketch; tracing dependencies, exporter and sampling still need configuration.

Implementation sketch

@Bean
RestClient rateClient(RestClient.Builder builder) {
    return builder.baseUrl("https://rate-service.internal")
        .build();
}

Cost and verification

Tracing adds context propagation and exporter traffic. A low sample rate reduces storage but can hide individual failures; use logs and metrics for unsampled requests.

Common Mistakes

• Do not construct a new unmanaged RestClient and assume Boot propagation follows it.
• Do not treat trace headers as an identity source.
• Do not put secrets or high-cardinality personal data into span tags.

Read next

Spring Boot observation context across @Async and Reactor handoffs, Spring async trace context: follow work across executor threads, Spring RestClient request factories: pin the transport you test, Spring Boot metrics: bound tag values instead of tracking each receipt.