redis is listed at https://docs.dify.ai/getting-started/install-self-hosted/environments as follows. But it's not clear what exactly redis is used for. For example ...

Nginx web server with production-ready optimization MySQL 8.0+ with secure setup and performance tuning PHP 8.3+ with FPM, OPcache and WordPress extensions Ubuntu/Debian family support (20.04, 22.04, ...