[opentelemetry-php-contrib] Incorrect trace boundaries for Symfony HttpKernel auto instrumentation

[petrisorciprian-vitals]

Describe your environment

PHP 8.2.24 (cli) (built: Sep 27 2024 04:16:10) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.2.24, Copyright (c) Zend Technologies
    with Zend OPcache v8.2.24, Copyright (c), by Zend Technologies
    with Xdebug v3.3.1, Copyright (c) 2002-2023, by Derick Rethans

Relevant packages:

• open-telemetry/opentelemetry-auto-symfony
• open-telemetry/opentelemetry-auto-psr14

Steps to reproduce
Install both packages in a Symfony project, enable otel SDK autoloader and fire a request to the application.

What is the expected behavior?
A single trace for the request.

What is the actual behavior?
Two traces, one for the request itself, and one for the Symfony\Component\HttpKernel\Event\TerminateEvent emitted by Symfony at the end of Symfony\Component\Runtime\Runner\Symfony\HttpKernelRunner.

Additional context

The problem seems to be the hooks set up in open-telemetry/opentelemetry-auto-symfony:
It hooks into the HttpKernel::handle method. The post hook detaches the scope via scope->detach().

The TerminateEvent is emitted by Symfony however after the post hook runs for HttpKernel::handle, at which point it no longer has a context with a traceId available, so a new one seems to be generated.

Potential solution

Since the HttpKernel extends TerminableInterface which exposes a terminate function, I propose removing the post hook from HttpKernel::handle and registering it on HttpKernel::terminate instead, so that this event is captured properly by opentelemetry-auto-psr14 and part of the same request trace instead of an individual one.