Specifying peer.service in automatic fetch() OTEL instrumentation

[demostanis]

symfony-auto-instrumentation sets peer.service in their HTTP client instrumentation (here), which allows Grafana to show this:

Deno currently only shows the method name, which makes the trace harder to understand when there are a lot of spans.

Note: I can't test this myself since trying to build Deno results in it getting OOM'ed (even in GitHub codespaces) or getting weird linker errors.

[demostanis]

should be just a matter of:

From caaadf21570aff95d0391682d176979b2bdc7953 Mon Sep 17 00:00:00 2001
From: demostanis <demostanis@protonmail.com>
Date: Fri, 26 Sep 2025 09:30:16 +0200
Subject: [PATCH] specify peer.service in automatic HTTP client OTEL
 instrumentation

---
 ext/telemetry/util.ts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/ext/telemetry/util.ts b/ext/telemetry/util.ts
index 54612a4..c354698 100644
--- a/ext/telemetry/util.ts
+++ b/ext/telemetry/util.ts
@@ -17,6 +17,7 @@ export function updateSpanFromRequest(span: Span, request: Request) {
   );
   span.setAttribute("url.path", url.pathname);
   span.setAttribute("url.query", StringPrototypeSlice(url.search, 1));
+  span.setAttribute("peer.service", url.host);
 }
 
 export function updateSpanFromResponse(span: Span, response: Response) {
-- 
2.50.0

[lucacasonato]

I think this only works if the url.host is the actual peer's service name? SemConv says this:

The service.name of the remote service. SHOULD be equal to the actual service.name resource attribute of the remote service if any.

https://opentelemetry.io/docs/specs/semconv/registry/attributes/peer/#peer-service

[demostanis]

I don't think there's a better way to automatically get the peer's service name for a HTTP request other than by checking the url.host, as symfony-auto-instrumentation currently does.

[demostanis]

What other solution would there be, instead of only showing the HTTP method?
Currently:

ipinfo.io and the service inside my cluster have more understandable names than "POST"

[demostanis]

I was able to temporarily get the same result by applying this Grafana Alloy filter:
set(attributes["peer.service"], URL(attributes["url.full"])["url.domain"]) where attributes["url.full"] != nil

However I still think having this by default in Deno isn't a bad idea.