The service models are just a sliding scale of who patches what:

Model	Provider runs	You run	Examples
IaaS	hardware, DC, virtualisation	OS, patches, apps, data	EC2, Azure VM, GCE
PaaS	+ OS/runtime/middleware	app + data	App Service, Cloud Run
SaaS	everything incl. the app	users, data, config	mail, CRM

Shared responsibility: you always keep data, and the higher the model the less you control underneath. Deployment models: public, private, hybrid (the enterprise default in practice), community.

Network implications: VPC/VNet + subnets + security rules replace racks and patch panels; connectivity via site-to-site VPN or private circuits (Direct Connect/ExpressRoute); scale mechanisms are load balancers and auto-scaling groups.