Public cloud is multi-tenant (AWS, GCP, Azure). Private cloud is single-tenant (on-prem or hosted). Hybrid cloud is a mix. The right pick depends on compliance requirements, scale, and budget.
Table of contents
- Public cloud
- Private cloud
- Hybrid cloud
- The decision
- The cost comparison
- The migration path between them
- The compliance landscape
- FAQ
Public cloud
Multi-tenant infrastructure shared with other customers. AWS, GCP, Azure, DigitalOcean, RunxBuild.
Pros:
- Pay for what you use.
- No upfront capital.
- Elastic scaling.
- Managed services (databases, queues, AI).
Cons:
- Less control over the underlying infrastructure.
- Compliance limitations for some industries.
- Ongoing operational cost (vs. capital expense).
The team that picks public cloud has the fastest path to production. The team that needs compliance or sovereignty picks private cloud.
Private cloud
Single-tenant infrastructure, usually on-prem but can be hosted. OpenStack, VMware, or a hosted private cloud (RunxBuild Dedicated, AWS Outposts).
Pros:
- Full control over the infrastructure.
- Compliance-friendly (data doesn’t leave the boundary).
- Predictable cost at scale.
Cons:
- High upfront capital expense.
- Operational overhead (the team runs the infrastructure).
- Slow to scale.
The team that picks private cloud has specific compliance, sovereignty, or scale requirements. The team that picks private cloud without a specific reason is doing extra work.
Hybrid cloud
A mix of public and private, usually with data or applications moving between them.
The common pattern:
- Public cloud for elastic workloads. Web tier, API tier, batch jobs.
- Private cloud for sensitive data. Customer data, regulated data, on-prem databases.
- A connection between them. VPN, Direct Connect, ExpressRoute.
Pros:
- Best of both worlds.
- Sensitive data stays on-prem.
- Elastic workloads scale in the public cloud.
Cons:
- Complex to operate.
- Latency between public and private.
- Two infrastructure stacks to maintain.
The team that picks hybrid cloud has a specific reason. The team that picks hybrid without a specific reason is the team that ends up paying for both.
The decision
The right pick:
- Default to public cloud. AWS, GCP, Azure, or RunxBuild. The team that starts with public cloud moves to hybrid or private if a specific need emerges.
- Private cloud if compliance demands it. Healthcare (HIPAA in some cases), government (FedRAMP), finance (PCI-DSS for some workloads).
- Hybrid cloud if you have existing on-prem investment. The team that has spent $10M on a data center doesn’t decommission it overnight; hybrid is the path.
- Multi-cloud if you have a specific reason. Best-of-breed services, vendor leverage, regional presence.
The cost comparison
Real numbers for a 100-CPU, 1 TB RAM workload:
- Public cloud. $5-10K/month. No upfront. Pay as you go.
- Private cloud (capital expense). $200-500K upfront for the hardware. Plus $5-10K/month for power, cooling, and ops.
- Hosted private cloud. $8-15K/month. No upfront. The team that picks hosted private has the capital-experience of on-prem with the operating-experience of public.
The break-even for private vs public is usually 3-5 years. The team that needs to be running in 3 months picks public; the team that needs to run for 10 years and has specific compliance picks private.
The migration path between them
The team that needs to migrate between cloud models:
Public to private. Rarely worth it. The team that moves from public to private usually has a specific compliance or cost reason. The migration is essentially building a private cloud from scratch.
Public to hybrid. Move sensitive workloads to private; keep elastic workloads in public. The team that has compliance requirements uses this pattern.
Hybrid to public. Move all workloads to public; decommission the private infrastructure. The team that finds the private cloud underutilized uses this.
Private to public. Common migration. The team that wants to exit the data center business uses this. Lift-and-shift or re-platform depending on the workload.
Each migration has different cost, risk, and timeline profiles. The team that plans ahead of time has a smooth migration.
The compliance landscape
Compliance is the main driver of cloud model choice:
Public cloud. Shared responsibility model. Cloud provider handles physical security; team handles configuration. Certifications (SOC 2, ISO 27001, HIPAA, PCI-DSS) are usually available.
Private cloud. Full control. The team can implement any compliance framework without depending on a provider’s certifications. The cost: building the infrastructure to support the framework.
Hybrid cloud. Mixed compliance posture. Some workloads in public (with provider’s certifications); some in private (with full control). The right choice when different workloads have different compliance requirements.
Government clouds. AWS GovCloud, Azure Government, GCP Government. Isolated regions with specific compliance certifications (FedRAMP, IL4, IL5). The team that sells to the US government uses these.
The team that maps workloads to compliance requirements picks the right cloud model. The team that picks the cloud model first and figures out compliance later has surprises.
FAQ
What is public cloud?
Multi-tenant infrastructure shared with other customers. AWS, GCP, Azure, DigitalOcean. The team that uses public cloud shares the underlying hardware with other customers (but in isolated virtual networks).
What is private cloud?
Single-tenant infrastructure dedicated to one customer. On-prem or hosted. The team that uses private cloud has its own hardware, isolated from other customers.
What is hybrid cloud?
A mix of public and private cloud, connected by a VPN or direct connection. The team that uses hybrid has some workloads on public cloud and some on private.
Which cloud model is best for a startup?
Public cloud. The team that picks public cloud has no upfront capital, scales elastically, and pays for what it uses. The team that picks private cloud for a startup has a specific reason (rare).
What is sovereign cloud?
A cloud provider that stores and processes data within a specific country’s borders. AWS European Sovereign Cloud, Google Sovereign Cloud, Microsoft Cloud Sovereignty. The team that has data sovereignty requirements uses these.
Is multi-cloud the same as hybrid cloud?
No. Multi-cloud is using multiple public clouds (AWS + GCP). Hybrid is mixing public and private. The two are often combined (hybrid multi-cloud), but they address different needs.
How long does a public-to-private migration take?
6-18 months depending on the workload count. The team that uses a phased migration (one app at a time) has lower risk than the team that tries to migrate everything at once.
If you are sizing the infrastructure for the kind of project this post covers, the RunxBuild hosting calculator is the right place to model the line items. The compute, the memory, the storage, the bandwidth, the database - each one is a separate number, and the team’s mental model for the platform is the sum of those numbers. The RunxBuild dashboard is where the team sees the actual usage in one place.
Useful related references: