Cloud service types and deployment models explained
SaaS, PaaS, IaaS and public, private and hybrid cloud - what each means and how to choose for 2026.
By the Telappliant team
Cloud has stopped being a single decision. UK businesses now run a mix of SaaS, IaaS and PaaS across public, private and hybrid deployments, and getting the combination wrong shows up as cost overruns, compliance gaps or applications that simply feel slow.
The three service types, in practical terms
- SaaS (Software as a Service): Microsoft 365, your CRM, your finance system - you consume the application, the provider runs everything underneath it
- PaaS (Platform as a Service): Azure App Service, managed databases - your developers deploy code without managing servers or patching
- IaaS (Infrastructure as a Service): Azure or AWS virtual machines, storage and networking - you still manage the operating system and above
The deployment models and where each fits
Public cloud (Azure, AWS, Google Cloud) is the default for most SMEs because it removes capital spend and scales on demand. Private cloud, whether hosted or on your own hardware, still matters where a specific regulatory or latency requirement rules out shared infrastructure. Hybrid cloud, keeping some workloads on-premise and some in public cloud, is common where legacy line-of-business systems cannot move yet or where data residency needs a UK-only environment.
How UK businesses actually mix these
- Email, collaboration and core productivity on Microsoft 365 SaaS
- Line-of-business applications on IaaS virtual machines, either lifted from an old server room or rebuilt cloud-native
- Custom development on PaaS to cut infrastructure management for the development team
- A private or hybrid slice for anything with strict data residency, latency or legacy dependency requirements
The cost trap nobody warns you about
Public cloud IaaS billed like an always-on server is usually more expensive than the server it replaced, unless you actively manage it: right-sizing instances, shutting down non-production environments out of hours, and using reserved pricing where usage is predictable. SaaS costs creep through unused licences and duplicate tools bought by different teams. Neither problem is solved by moving to cloud; both are solved by governance.
Security and compliance responsibility is shared, not transferred
Every deployment model divides responsibility between you and the provider. In SaaS, the provider secures the platform but you configure access, MFA and data sharing. In IaaS, you are responsible for almost everything above the physical hardware, including patching the operating system. Businesses that assume cloud means someone else handles security consistently fail Cyber Essentials and cyber insurance audits on exactly this point.
How to choose without a lengthy consulting exercise
- List each application and classify it: buy as SaaS if a good one exists, build on PaaS if you are developing custom software, lift to IaaS only when nothing else fits
- Flag anything with a genuine data residency or regulatory constraint before choosing a region or provider
- Decide hybrid only where there is a real technical or contractual reason, not as a default compromise
- Set a review point at month six, because most estates drift from the original plan within a year
