If you’ve encountered issues with Xdebug while working on a Symfony project ( particularly when PHPStorm is listening for Xdebug), you might have come across a “502 Bad Gateway” error from Nginx server. In this post, I’ll share how I resolved this problem.

My environment

I’m currently working on a Symfony 6.1 application within a dockerized environment:

  • nginx 1.19
  • php 8.1 fpm

Upon attempting to listen for Xdebug in PHPStorm, I encountered the following error in the FPM container:

[05-Mar-2024 09:56:20] WARNING: [pool www] child 9 exited on signal 11 (SIGSEGV - core dumped) after 10.753537 seconds from start,

Simultaneously, the browser displayed the following error:

ngnix error

The solution

After several hours of investigation, I pinpointed the root cause of the issue and discovered a solution. It turns out that there’s a bug within Xdebug 3.3.*, which has been documented in various tickets:

Given that I’m working in a dockerized environment, I needed to downgrade Xdebug within the Docker container, not on the host system.

Here’s what my Dockerfile looked like after the downgrade:

# ...

COPY --from=mlocati/php-extension-installer /usr/bin/install-php-extensions /usr/bin/install-php-extensions
RUN install-php-extensions \
        pdo \
        pdo_pgsql \
        pgsql \
        xdebug-3.2.2 \
        xsl \

# ...

Note how you specify the Xdebug version to use to 3.2.2. Remember, you’ll need to rebuild and restart your container for the changes to be applied.


The root cause of the problem lies in a bug within Xdebug 3.3.*. Downgrading to Xdebug 3.2.2 effectively resolved the issue.