Kubernetes automatically manages clusters to align with their desired state through the Kubernetes control plane. The master node will then communicate the desired state to the worker nodes via the API. This developer interaction uses the command line interface (kubectl) or leverages the API to directly interact with the cluster to manually set the desired state.
To define a desired state, JSON or YAML files (called manifests) are used to specify the application type and the number of replicas needed to run the system.ĭevelopers use the Kubernetes API to define a cluster’s desired state. Resources that should be provided for these apps.Images that these applications will need to use.Applications and workloads that should be running.The desired state of a Kubernetes cluster defines many operational elements, including: To work with a Kubernetes cluster, you must first determine its desired state. The master node runs the API server, scheduler and controller manager, and the worker nodes run the kubelet and kube-proxy. These six components can each run on Linux or as Docker containers. Consistent and highly available Kubernetes backing store. Implements the Kubernetes Service concept across every node in a given cluster. Kube-proxy: Manages network connectivity and maintains network rules across nodes.Takes a set of provided PodSpecs and ensures that their corresponding containers are fully operational. Kubelet: Ensures that containers are running in a Pod by interacting with the Docker engine , the default program for creating and managing containers.Manages controllers such as node controllers, endpoints controllers and replication controllers. Controller manager: Runs controller processes and reconciles the cluster’s actual state with its desired specifications.Makes note of Pods with no assigned node, and selects nodes for them to run on. Scheduler: Places containers according to resource requirements and metrics.Serves as the front end of the Kubernetes control plane. API server: Exposes a REST interface to all Kubernetes resources.For this reason, they are ideal in situations involving complex projects or multiple teams.Ī Kubernetes cluster contains six main components: Namespaces enable users to divide cluster resources within the physical cluster among different teams via resource quotas. For testing, the components can all run on the same physical or virtual node.Ī namespace is a way for a Kubernetes user to organize many different clusters within just one physical cluster. For production and staging, the cluster is distributed across multiple worker nodes. There must be a minimum of one master node and one worker node for a Kubernetes cluster to be operational. They can either be virtual machines or physical computers, all operating as part of one system. Worker nodes perform tasks assigned by the master node. The worker nodes are the components that run these applications. The master node is the origin for all task assignments. The master node controls the state of the cluster for example, which applications are running and their corresponding container images. These nodes can either be physical computers or virtual machines, depending on the cluster.
Kubernetes clusters are comprised of one master node and a number of worker nodes. Instead, they are able to share operating systems and run anywhere. Kubernetes containers are not restricted to a specific operating system, unlike virtual machines. Kubernetes clusters allow containers to run across multiple machines and environments: virtual, physical, cloud-based, and on-premises. In this way, Kubernetes clusters allow for applications to be more easily developed, moved and managed. They are more lightweight and flexible than virtual machines. Containerizing applications packages an app with its dependences and some necessary services. A Kubernetes cluster is a set of nodes that run containerized applications.