Kubernetes (often abbreviated as k8s) is open source system started by Google to fill this need. When an application grow beyond a single host , a need arisen for what has come to be called an orchestration system. An orchestration system helps users view a set of hosts as unified programmable relaible cluster
Kubernetes cluster include following:
Kubernetes master service: These centralized services provide an API collect and surface the current state of the cluster and assign pods to node. Users mostly connect to the master API, this provides a unified view
Master Storage [etcd]: This is persistent storage. Currently all the state are preserved and store in etcd
Kubelet: This agent runs on every node, and is responsible for driving Docker, reporting status to the master and setting up node-level resources.
Proxy: This also run in each node and provides local container a single network endpoint to reach an array of pods.
pods: A group of containers that must be placed on a single node and work together as a team. Allowing a set of containers work closely together on a single node.
As user interacts with a Kubernetes master through kuectl that calls Kubernetes API. The master is responsible for storing a description of what users want to run.On each worker node in a cluster kubelet and proxy would be running. Kubelet is responsible for driving Docker and setting up other node-specific states like storage volumes. Proxy is responsible for providing local end point.
Kuberentes works to manage pods. Pods are a grouping of compute resource that provides context for a set of containers. Users can use pods to force a set of containers that work as a team to be scheduled on a single physical node.
Pods define a shared network interface. Unlike regular containers, containers in a pod all share the same network interface. This allows easy access across container using localhost. It also means that different containers in same pod cannot use the same network port.
Storage volume are defined as part of the pod. These volumes can be mapped into multiple containers as needed.