> For the complete documentation index, see [llms.txt](https://experience-digital-transform.gitbook.io/experience-digital-transformation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://experience-digital-transform.gitbook.io/experience-digital-transformation/cloud-for-dpi/chapter-4/why-kubernetes.md).

# Why Kubernetes

A **virtual machine** provides an operating system, CPU, memory and network interfaces. It does not place application processes, maintain copies or roll out new versions.

**Containers** change the packaging unit. A **container image** carries an application and its userspace dependencies, while containers normally share the host kernel. One virtual machine can run several isolated containers without a guest operating system for every copy. Workload behaviour, security and isolation still determine the suitable boundary. [\[19\]](https://csrc.nist.gov/pubs/sp/800/190/final)

<figure><img src="https://1406653965-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FkZFMZ3jCMUwHtTN0sL4J%2Fuploads%2Fgit-blob-267741292bb18b2273730f46be3a22fdc5ca5cd2%2Ffinal.png?alt=media" alt="Several virtual machines each package an application with a guest operating system, while one virtual machine can host several containers above a shared kernel."><figcaption><p>Figure 1. Virtual machines isolate complete guest systems. Containers let several packaged applications share one host kernel while retaining separate runtime boundaries.</p></figcaption></figure>

**Kubernetes** adds a common lifecycle system for containers. Its smallest deployable workload unit is a **Pod**, which holds one or more tightly related containers. A **Node** is a machine that can run Pods. A **Deployment** states the desired number of interchangeable application copies and the update strategy. A **Service** gives a changing set of Pods a stable network identity. [\[9\]](https://kubernetes.io/docs/concepts/services-networking/service/)[\[16\]](https://kubernetes.io/docs/concepts/workloads/controllers/deployment/)[\[18\]](https://kubernetes.io/docs/concepts/workloads/pods/)

The Kubernetes **scheduler** selects eligible Nodes for Pods. **Controllers** compare **declared state** with **observed state**. They can replace a failed Pod when capacity exists; missing Node capacity still requires the infrastructure lifecycle. [\[14\]](https://kubernetes.io/docs/concepts/overview/)[\[15\]](https://kubernetes.io/docs/concepts/overview/components/)

**Video companion:** [C4-I1, From virtual machines to a Kubernetes platform](https://git.vanillacore.net/giga/content/src/branch/main/chapter-4/VIDEO_SCOPES.md#c4-i1-from-virtual-machines-to-a-kubernetes-platform)

Kubernetes is a workload platform above IaaS. Teams use Kubernetes resources, while storage, load balancing, failure domains, accelerators and capacity still depend on IaaS capabilities.


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