**Kubernetes** is the open source container orchestration system that schedules, scales, and manages containerised workloads across clusters of machines. Originally from Google (built on Borg), it is now the de facto standard for running production services in any cloud — public, private, or hybrid. --- ### First Principle: Every workload should declare what resources it needs. The platform decides where it runs. Kubernetes separates the concerns of *what to run* (the application spec) from *where to run it* (the scheduler's decision). Operators declare desired state; Kubernetes continuously reconciles actual state to match it — restarting crashed containers, rescheduling evicted pods, scaling replicas up and down automatically. --- ### Key Considerations - **Control Plane**: API Server, etcd (distributed state store), Scheduler (assigns pods to nodes), Controller Manager (reconciliation loops), and Cloud Controller (cloud provider integration). - **Data Plane**: kubelet (agent on each node) and kube-proxy (service networking) run on every worker node, executing the scheduler's decisions. - **Workload Types**: Deployments (stateless), StatefulSets (stateful, ordered), DaemonSets (one per node), Jobs (batch), CronJobs (scheduled batch). - **Extensibility**: The API is extensible via Custom Resource Definitions (CRDs) and operators — enabling [[ArgoCD]], [[KubeVirt]], [[Longhorn]], [[Cilium]], and [[cert-manager]] to integrate deeply. - **Networking**: [[Cilium]], Calico, or Flannel handle pod networking. [[MetalLB]] provides load balancer services on bare metal. - **At Hyperscaler Scale**: Every major cloud offers managed Kubernetes. [[OKD]]/OpenShift and [[Rancher]] are the main open source management layers. --- ### How It Fits ``` [[Bare Metal]] / [[VMs]] (physical or virtual nodes) → Kubernetes (scheduling, orchestration, self-healing) → [[Cilium]] (networking) | [[Longhorn]] (storage) → [[ArgoCD]] (GitOps) | [[Prometheus]] (monitoring) ``` [[Docker Containers]] | [[KubeVirt]] | [[Rancher]] | [[ArgoCD]] | [[Cilium]] | [[Longhorn]] | [[Open Source Hyperscaler MoC]]