Using Classic Mode

Without any additional configuration, FrankenPHP operates in classic mode. In this mode, FrankenPHP functions like a traditional PHP server, directly serving PHP files. This makes it a seamless drop-in replacement for PHP-FPM or Apache with mod_php.

Similar to Caddy, FrankenPHP accepts an unlimited number of connections and uses a fixed number of threads to serve them. The number of accepted and queued connections is limited only by the available system resources. The PHP thread pool operates with a fixed number of threads initialized at startup, comparable to the static mode of PHP-FPM. It’s also possible to let threads scale automatically at runtime, similar to the dynamic mode of PHP-FPM.

Queued connections will wait indefinitely until a PHP thread is available to serve them. To prevent that, you can use the max_wait_time configuration to limit how long a request may wait for a free PHP thread before being rejected. Additionally, you can set a reasonable write timeout in Caddy.

Each Caddy instance will only spin up one FrankenPHP thread pool, which will be shared across all php_server blocks.