Docker

Overview Docker packages an application and its dependencies into a portable container image and runs it on a single host, while Kubernetes schedules, scales, and heals many containers across a cluster of machines. They aren’t direct substitutes — Kubernetes typically runs containers built by Docker (or another OCI-compatible tool), sitting one layer above it. Comparison Diagram DockerKubernetesSingle Hostapp Aapp Bapp Cidledocker runmanual, per-hostif host dies, all lostControl PlaneNode 1Node 2Node 3scheduler places podsauto-reschedules on failuredeclarative, cluster-wide Comparison Table Aspect Docker Kubernetes Core purpose Build, package, and run containers from a single image spec Orchestrate and manage many containers across a fleet of machines Unit of work Container, defined by a Dockerfile and run via docker run Pod, a group of one or more containers scheduled together Deployment scope Single host (or manually scripted across hosts) Multi-node cluster with a control plane scheduling workloads Configuration model Imperative CLI commands or docker-compose.yml Declarative YAML manifests reconciled continuously toward desired state Networking & discovery User-defined bridge networks and container name resolution Cluster-wide Services, DNS, and Ingress across nodes Scaling Manual — start more containers or use docker-compose scale Automated via ReplicaSets and Horizontal Pod Autoscaler Failure recovery No built-in restart across host failure; relies on restart policies per host Self-healing — reschedules pods automatically if a node or container fails Rollouts & updates Rebuild image and manually restart containers Rolling updates and rollbacks managed declaratively per Deployment Key Differences Docker operates at the level of a single container; Kubernetes operates at the level of a cluster. Kubernetes doesn’t replace Docker — it typically schedules containers that Docker (or another container runtime) built and runs. Docker’s model is largely imperative, while Kubernetes is fundamentally declarative, continuously reconciling actual state to desired state. Kubernetes adds self-healing and autoscaling that plain Docker has no native concept of. For a single app on one machine, Kubernetes’ control plane overhead is often unjustified complexity. When to Use Each Docker ...