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Faster environment with xDebug and Docker

I have to admit that I've always been lazy when it came to set up xDebug as it felt tedious the few times I've to do it. It made me an almost perpetual member of the var_dump debug team.

Nevertheless, the last time I had to set it up was more straightforward, thanks to PhpStorm, and I don't think the difficulty to set up is a valid excuse anymore.

I then had a debugger…

And I had a speed issue. My tests were running slower than before, and every request took way too much time. Using Docker on OSX didn't help at all.

I found a few tips that helped me go back to the same state as before.

So …

Tips 1: Do not start xDebug

Ahah… Yes, you can thank me for this one. The best way to avoid xDebug slowing everything down is by not having xDebug running. So, disable it by commenting the path to the extension in the .ini file loading it. Another idea is that if you have an xdebug.ini file in the PHP configuration directory, rename it to something else, xdebug.ini.back, for instance.

This being said, how can we manage to start xDebug when needed?

Tips 2: Use the on-demand PhpStorm mode when debugging tests

As explained in the PhpStorm documentation, an "on-demand" mode is available. It will enable xDebug only when debugging tests, which will allow running your test at full speed most of the time.

I'll let you dig in the documentation as it will be better explained than if I do it myself.

Tips 3: Use the on-demand mode without PhpStorm

PhpStorm is not doing magic for the "on-demand" mode but taking advantage of the -d PHP CLI option. The -d allows defining an entry in the PHP configuration. When starting the "on-demand" mode, PhpStorm adds -d to the PHP CLI options, which enables the extension. You can do the same thing if you're running your tests without PhpStorm.

As an example here is how you can run PhpUnit with xDebug activated:

php -d ./vendor/bin/phpunit
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You'll probably need to pass more options if you want to connect xDebug to a debugger client, so this not as convenient as running it through PhpStorm as it sets everything needed to work out the box. As an example, here are all the option passed by PhpStorm when I start tests in debug mode :

-d -d xdebug.remote_enable=1 \
-d xdebug.remote_mode=req -d xdebug.remote_port=9100 \
-d xdebug.remote_host=host.docker.internal
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This is still a good option if you need xDebug without a client listening. I guess the primary use case would be for coverage reports.

Tips 4: Enable xDebug with an environment variable in your docker container

Going in the container and modifying files every time you need to enable or disable xDebug is cumbersome. I've tested another option for the last few weeks, and it works very well.

I've modified my PHP Dockerfile to add an entry point script, which is run when the container starts and can access environment variables.

The entry point script looks for an environment variable and decides to rename, or not, the xdebug.ini file in the PHP configuration directory.

As an example, here is the file I'm using in a php5.6 container. You'll probably need to adapt it to suit your container.

set -e

if [[ ! -z "$DISABLE_XDEBUG" && "$DISABLE_XDEBUG" = true && -f "/etc/php/5.6/mods-available/xdebug.ini" ]]; then

mv /etc/php/5.6/mods-available/xdebug.ini /etc/php/5.6/mods-available/xdebug.ini.back

cat >&2 <<EOF
⚠️  xDebug is disabled

elif [[ -z "$DISABLE_XDEBUG" || "$DISABLE_XDEBUG" = false && -f "/etc/php/5.6/mods-available/xdebug.ini.back" ]]; then
mv /etc/php/5.6/mods-available/xdebug.ini.back /etc/php/5.6/mods-available/xdebug.ini

exec "$@"
And the Dockefile is edited to include the entry point:

COPY ./ /
CMD ["php-fpm5.6"]
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The container can be started either with docker-compose or docker run and xDebug activated by setting the environment variable DISABLE_XDEBUG to false and disabled by setting it to true. When the variable is missing, xDebug will stay activated.

We now have a convenient way to enable xDebug only when needed and save some precious time not waiting in front of loading pages. The only thing required is to change the value of the variable and restart the container.

Extra tip

xDebug settings can be overridden using the XDEBUG_CONFIG environment variable, which means there is no need to update the xDebug config file every time you have to change a setting or if you and your teammates need different settings.

The best example is probably the remote_host. According to how you run docker, this setting could be a changing IP address or host.docker.internal if you're using Docker for Mac.

In order to set the remote host to host.docker.internal the XDEBUG_CONFIG should be set remote_host=host.docker.internal.

I hope all these tips will help you improve the speed of your development environment.

This post was originally posted on my blog

Picture by Paolo Candelo

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