Public Cloud
A public cloud is owned and operated by a third-party cloud provider — like Microsoft Azure, Amazon Web Services, or Google Cloud. The infrastructure is shared among multiple customers (tenants) over the public internet.
When most people say "the cloud," they mean the public cloud. You sign up, provide a credit card, and start using resources in minutes. Everything is managed by the provider — you just consume it.
Key Characteristics
- Owned and operated by the cloud provider (Microsoft, Amazon, Google)
- Shared infrastructure — multiple organisations on the same hardware
- Accessible over the public internet
- Pay-as-you-go pricing — no upfront capital investment
- Massive scale — resources available on demand, globally
Advantages
- No upfront cost — No hardware to buy, no data centre to build
- Infinite scale — Need 10,000 servers? Azure has them ready
- No maintenance — The provider handles hardware failures, updates, security
- Global reach — Deploy in 60+ regions worldwide with a few clicks
- High reliability — Built-in redundancy and SLA-backed uptime
Disadvantages
- Less control — You can't physically access the hardware
- Data sovereignty concerns — Your data lives in the provider's data centres
- Compliance challenges — Some industries (banking, defence) have strict data residency laws
- Internet dependency — Requires reliable internet connectivity
Private Cloud
A private cloud is cloud infrastructure that is dedicated exclusively to a single organisation. It's not shared with anyone else. The organisation either owns it and runs it in their own data centre, or pays a provider to host a dedicated environment just for them.
Think of it as owning your own building vs renting space in a shared office tower. More expensive, more control, more security.
Key Characteristics
- Dedicated to a single organisation — no shared tenancy
- Can be hosted on-premises (in your own data centre) or hosted by a provider
- Organisation has full control over hardware, security, and configuration
- Higher cost — you pay for dedicated resources whether or not you use them
Advantages
- Full control — You control every layer of the stack
- Data sovereignty — Your data never leaves your own infrastructure
- Regulatory compliance — Meets strict government and financial regulations
- Custom security policies — Implement any security controls you need
Disadvantages
- High upfront cost — You're buying hardware and building infrastructure
- Limited scale — You can only scale as far as your hardware allows
- Maintenance burden — Your team is responsible for everything
- Slower to deploy — Procurement and setup take weeks or months
Hybrid Cloud
Hybrid cloud combines public cloud and private cloud (or on-premises infrastructure), connected together so that data and applications can flow between them. It's the best of both worlds — keep sensitive workloads on-premises or in a private cloud, and burst to the public cloud when you need extra capacity or want to run less sensitive workloads.
Key Characteristics
- Combination of public cloud and private cloud / on-premises
- Workloads can move between environments based on need
- Connected via secure network links (VPN or ExpressRoute)
- Organisations can choose where each workload runs
Advantages
- Flexibility — Run sensitive data on-prem, burst to cloud for extra capacity
- Compliance — Keep regulated data on private infrastructure
- Cost optimisation — Use cloud only when needed; avoid over-provisioning on-prem
- Gradual migration — Move workloads to cloud at your own pace
Disadvantages
- Complexity — Managing two environments is significantly harder
- Higher cost — You still pay for on-premises infrastructure plus cloud usage
- Security complexity — Data moving between environments must be secured
- Network dependency — Reliable connectivity between environments is critical
Multi-Cloud
Multi-cloud is a strategy where an organisation uses cloud services from more than one public cloud provider — for example, using both Azure and AWS simultaneously.
Side-by-Side Comparison
| Factor | Public Cloud | Private Cloud | Hybrid Cloud |
|---|---|---|---|
| Ownership | Cloud provider | Organisation | Both |
| Tenancy | Multi-tenant (shared) | Single-tenant (dedicated) | Both |
| Cost model | Pay-as-you-go (OpEx) | Upfront investment (CapEx) | Mixed |
| Scalability | Virtually unlimited | Limited by hardware | Flexible |
| Control | Low | Full | Mixed |
| Security control | Shared with provider | Full control | Mixed |
| Setup time | Minutes | Weeks to months | Varies |
| Best for | Startups, agile teams | Banks, govt, defence | Enterprise migration |
When to Use Which?
| Scenario | Best Model | Why |
|---|---|---|
| Startup launching a new product | Public | Zero upfront cost, fast deployment, easy scaling |
| Bank storing customer financial data | Private | Data sovereignty, regulatory compliance |
| Enterprise migrating to cloud gradually | Hybrid | Move workloads at own pace, keep sensitive data on-prem |
| Government defence application | Private | Classified data cannot go to shared infrastructure |
| E-commerce site with seasonal peaks | Public or Hybrid | Scale out during sales events, scale back after |
| Hospital — patient portal + patient records | Hybrid | Portal on public cloud, records on private for compliance |