Three SaaS clients on the same shared Kubernetes cluster at the host. A container escapes (privileged: true or runc CVE): neighbourhood at risk. Same load on dedicated VMs on hardened hypervisor: blast radius stops at the VM — at RAM and operations cost.
Container = process isolation. VM = machine isolation. The chosen boundary defines your trust model.
Containers: density and velocity
Docker, containerd — immutable image, fast deployment. Strengths: density, CI/CD, microservices, same kernel. Weaknesses: shared kernel, config error (mounted docker.sock), vulnerable image propagation. Hosting: managed Kubernetes, Docker on VPS, container PaaS.
VM: virtual hardware boundary
KVM, VMware, Hyper-V — full guest OS. Strengths: strong isolation, different kernels, compliance, hostile multi-tenant. Weaknesses: RAM/CPU overhead, slow boot, patch per machine. Hosting: VPS, cloud IaaS, Kubernetes worker nodes.
| Criterion | Container | VM |
|---|---|---|
| Isolation | Process | Machine |
| Density | High | Low |
| Kernel patch | Once on host | Per guest + host |
| Hostile multi-tenant | Risky alone | Preferred |
Frequent boundary mistakes
Root container with host network. Exposed Docker socket. Undersized VM sharing disk without encryption. Assumed "isolation" without image scanning.
The climax: boundary follows trust level
Decide and move forward without blind spots
First classify workloads: same trust zone or not. Choose containers if Kubernetes is mature in your organisation; VMs if tenants are separate. Ban privileged mode and docker.sock mount in production. Finally compare managed EU Kubernetes or KVM VPS by criticality via the compare tool and directory.
Frequently asked questions
Container = VM isolation?
No — shared kernel; VM isolates at hypervisor with full guest OS.
When choose VM?
Hostile multi-tenant, strict compliance, heterogeneous OS, or legacy needing virtual hardware isolation.
Docker between trusted microservices?
Yes with good practices — standard internal Kubernetes where container security is mastered.
Hosting impact?
VM uses more RAM; containers densify; Kubernetes often combines both on VM nodes.
The right boundary is not the lightest — it is where compromise stops before the neighbour.