Symfony 5 "The connection was reset" (net::ERR_CONNECTION_RESET) if build missing caused by monolog

I ran into a really mad problem on a customer's local intranet running on Windows XAMPP (well yes it's not for production, I know, but wasn't my choice, but I have to deal with it).

The Symfony 5 application was running successfully on the development server (symfony serve), but on XAMPP it didn't want to work.

TL;DR:

See https://github.com/symfony/monolog-bundle/issues/412

Browsers showed:

Problem loading page: The connection was reset (net::ERR_CONNECTION_RESET)

after it loaded and loaded...

Errorlog said:

 [mpm_winnt:notice] [pid 7864:tid 548] AH00428: Parent: child process 1272 exited with status 3221225725 -- Restarting.

So I set the application up on other environments and it simply worked. Bot not on XAMPP on windows.

3 Things you should check!

1. If you're using symfony/webpack-encore-bundle, you should ensure that you run

yarn install
yarn run build

or via npm

npm i
npm run build

as I had a similar error when the CSS / JS was missing in a test.

2. Read / follow the issue I created here in https://github.com/symfony/monolog-bundle: https://github.com/symfony/monolog-bundle/issues/412

3. Increase the following values like this, as this will presumably fix the problem while it's still unclear why monolog needs these resources even in prod

<IfModule mpm_winnt_module>
    ThreadsPerChild        250
    MaxConnectionsPerChild   0
    ThreadStackSize 8388608
</IfModule>

as documented here:

• https://stackoverflow.com/a/43120319/10031165
• https://serverfault.com/questions/105908/how-do-you-increase-the-apache…
• https://stackoverflow.com/questions/5058845/how-do-i-increase-the-stack…

I hope I was able to save you from this nightmare... really mad issue, which made me tired ;)

UPDATE

Also note this related Symfony Bug on windows:

https://github.com/symfony/symfony/issues/42242