otelhttp: Deprecate DefaultClient (#8140)

Co-authored-by: Flc゛ <[email protected]>
Co-authored-by: Robert Pająk <[email protected]>
Co-authored-by: Damien Mathieu <[email protected]>

Author: 4 people

CHANGELOG.md

@@ -32,6 +32,8 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - `WithRouteTag` in `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp` is deprecated.
   The route is already added automatically for spans.
   For metrics, the alternative is to use the `WithMetricAttributesFn` option. (#8117)
+- `DefaultClient` in `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp` is deprecated.  
+  Use a custom `*http.Client` with `otelhttp.NewTransport(http.DefaultTransport)` instead. (#8140)
 
 ### Removed
 

instrumentation/net/http/otelhttp/client.go

@@ -14,6 +14,10 @@ import (
 // DefaultClient is the default Client and is used by Get, Head, Post and PostForm.
 // Please be careful of initialization order - for example, if you change
 // the global propagator, the DefaultClient might still be using the old one.
+//
+// Deprecated: [DefaultClient] will be removed in a future release.
+// Create your own *http.Client with Transport = otelhttp.NewTransport(http.DefaultTransport)
+// instead of relying on this global variable.
 var DefaultClient = &http.Client{Transport: NewTransport(http.DefaultTransport)}
 
 // Get is a convenient replacement for http.Get that adds a span around the request.