This is a very simple Docker container that logs incoming POST requests to a file. In fact, any requests are logged.
To make the log directory persistent, mount a persistent volume onto /var/www/html/logs.
Make sure the mounted directory allows writing by another user, ie. chmod -R 777.
Do your request to the root path, ie. /.
Logs are available under /logs/. Each request is stored in its own file, with headers and the PHP $_SERVER object.