Choosing between the open-source sovereign stack and managed public cloud

The decision and who faces it

Every engineering leader running EU workloads eventually asks the same question: do we keep renting compute from a hyperscaler, or do we build our own stack on hardware we control? The open-source sovereign stack, Proxmox for virtualization, Ceph for storage, OpenStack for cloud orchestration, and Kubernetes for container scheduling, gives you a way to run something functionally close to AWS or Azure, but on infrastructure you own or lease from an EU-based data center.

This decision usually surfaces for three types of teams: SaaS companies that hit a scaling point where cloud bills stop making sense, regulated businesses (fintech, healthcare, government contractors) that need to prove data never leaves EU jurisdiction, and platform teams that got burned by a pricing change or an outage they couldn't influence. None of these are edge cases anymore. We've written before about how cloud becomes more expensive than bare metal at certain scale, and the sovereign stack is often the mechanism teams use to make that switch real.

This isn't a binary choice between "open source" and "cloud." It's a choice between two operating models: build and operate your own platform, or consume infrastructure management services from a partner (or hyperscaler) who operates it for you. Both are valid. The right answer depends on team size, growth trajectory, and how much of your engineering time you're willing to spend on plumbing instead of product.

Option A: the open-source sovereign stack, explained fairly

The stack breaks down into four layers, each solving a different problem:

• Proxmox VE: virtualization layer. Runs KVM virtual machines and LXC containers with a web UI, clustering, and built-in backup. It's the layer most teams start with because it directly replaces VMware or bare-metal hypervisors.
• Ceph: distributed storage. Provides block, object, and file storage across a cluster of disks with no single point of failure. This is what lets you lose a node and keep serving reads and writes.
• OpenStack: cloud orchestration. Adds the API layer for compute, networking (Neutron), and identity (Keystone) that turns a pile of Proxmox/KVM hosts into something you can provision programmatically, the way you'd provision an EC2 instance.
• Kubernetes: container orchestration, usually running on top of VMs provisioned by the layers below.

Together, these give you a private cloud with self-service provisioning, live migration, snapshotting, and horizontal scaling, without a hyperscaler contract. Real examples: a fintech we worked with cut cloud costs by 65% moving core services onto a Proxmox and Ceph cluster, keeping only edge and CDN functions on public cloud (we covered the numbers in how a fintech startup cut cloud costs 65% with an open-source sovereign stack). Government and defense-adjacent contractors use this stack specifically because OpenStack's API compatibility lets them build tooling that looks like AWS automation but runs on hardware physically located in an EU data center, with no CLOUD Act exposure.

Real strengths

• No licensing lock-in. Proxmox has a subscription for support, not a per-core tax like VMware. Ceph and OpenStack are Apache-licensed.
• Full data sovereignty. You control the physical location, the network path, and who has access. No US parent company, no subpoena exposure.
• Cost predictability at scale. Once you're past a certain compute footprint (roughly 15-20+ VMs or equivalent, sustained), the economics of owned or leased hardware plus open-source software usually beat metered cloud pricing.
• No API rate limits or surprise deprecations. You're not waiting on a vendor's roadmap.

Real limits

• Operational burden is real and constant. Ceph in particular punishes teams that don't understand placement groups, replication factors, and failure domains. A misconfigured CRUSH map can turn a single disk failure into cluster-wide latency.
• You own the upgrade path. OpenStack releases every six months. Skipping releases makes upgrades harder, not easier. This is not "set and forget" software.
• Talent is scarce and expensive. Engineers who can debug a Ceph OSD flapping under load, or trace a Neutron networking issue through OVS, are a small pool. You either build this expertise in-house or hire a partner who already has it.
• Time to production-ready is measured in months, not days. Standing up a resilient three-node Ceph cluster with proper monitoring, backup, and disaster recovery testing is a project, not a weekend task.

Option B: managed public cloud (or managed cloud infrastructure via a partner)

The alternative is consuming infrastructure as a service, either directly from a hyperscaler (AWS, Azure, GCP, or an EU-based alternative like Scaleway or OVHcloud), or through a managed infrastructure partner who operates the underlying platform, sovereign stack or otherwise, on your behalf.

Real strengths

• Speed to provision. New compute, storage, and managed databases are available in minutes, not weeks.
• Managed services reduce operational surface. Managed Kubernetes (EKS, AKS, GKE, or an EU equivalent), managed databases, and managed load balancers remove entire categories of failure modes from your team's plate.
• Elastic scaling. Traffic spikes, seasonal e-commerce loads, and unpredictable SaaS growth are handled by autoscaling groups instead of manual capacity planning.
• Global reach without building it yourself. If you genuinely need presence in multiple continents, hyperscalers already have the points of presence.

Real limits

• Costs scale linearly, or worse, with usage. Egress fees, IOPS charges, and managed service premiums add up in ways that are hard to forecast. We've documented this in detail in cheap hosting vs managed cloud infrastructure: the real cost difference.
• Data sovereignty is harder to guarantee than the region toggle suggests. A US-headquartered provider's EU region doesn't remove CLOUD Act exposure. This is worth understanding fully before committing, and we've covered why EU region toggles don't solve data sovereignty on their own.
• Vendor roadmap risk. Pricing changes, feature deprecations, and API changes happen on the vendor's schedule, not yours.
• Less architectural control. You're working within the abstractions the provider gives you. Deep customization of networking or storage behavior is limited or unavailable.

Direct comparison

A decision framework

Use this to cut through the abstract debate and get to a concrete answer for your situation.

If you have fewer than 3 dedicated infrastructure engineers, running Ceph and OpenStack yourself is a risk you're probably underestimating. Either stay on managed public cloud, or bring in a partner who operates the sovereign stack for you as infrastructure management services, giving you the sovereignty benefit without the staffing requirement.

If your compute footprint is under roughly 10-15 VMs, the capex and operational overhead of a private Ceph/OpenStack cluster won't pay back quickly. Public cloud or a straightforward managed VPS setup is the more rational choice at this size.

If you're contractually or legally required to prove EU-only data residency (government tenders, DORA-regulated fintech, healthcare data under strict interpretations of GDPR), the sovereign stack, either self-run or via a managed infrastructure partner, is usually the only architecture that fully closes the CLOUD Act gap. Region toggles from US-headquartered providers do not satisfy this requirement on their own.

If your workload is bursty and unpredictable (flash sales, seasonal SaaS onboarding waves, marketing-driven traffic spikes), elastic public cloud, or a hybrid pattern with sovereign stack for baseline load and cloud for burst, will serve you better than a fixed-capacity private cluster.

If you're already spending 30%+ of cloud costs on egress, IOPS, or managed service premiums for steady-state workloads, model the sovereign stack seriously. This is the exact profile of teams who've cut costs 50-65% by moving core services onto owned infrastructure, as we detailed in our fintech cost optimization case study.

If you want the control of a sovereign stack without hiring a Ceph specialist, this is where a managed infrastructure partner earns its keep: you get OpenStack's API compatibility and EU data residency, but the 2am Ceph OSD alert goes to someone who's debugged it a hundred times before, not to your on-call engineer learning it live.

None of these paths is a permanent commitment. Plenty of teams run public cloud for years, then migrate core workloads to a sovereign stack once volume and compliance requirements justify it. The migration itself doesn't have to mean downtime, if you plan it as a phased cutover rather than a single event, an approach we walk through in our 6-phase zero downtime migration playbook.

Where this leaves you

The sovereign stack and managed public cloud aren't competing ideologies, they're tools that fit different operating constraints. Teams with the headcount and the compliance requirement get real value from owning Proxmox, Ceph, OpenStack, and Kubernetes end to end. Teams without that headcount get the same sovereignty and cost benefits by working with a partner who already operates that stack as a service.

Still weighing options for your stack? Book a 30-minute architecture call, no sales pitch.