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title: FrankenPHP Classic Mode: Drop-in PHP-FPM Replacement
description: Run FrankenPHP in classic mode as a drop-in replacement for PHP-FPM or Apache mod_php, with a fixed or autoscaling thread pool serving PHP files directly.
---
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 avoid this, you can use the max_wait_time configuration in FrankenPHP's global configuration to limit the duration a request can 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.