Controller: The management node of a cloud environment. Typically, you have one controller per cloud region or more in high-availability (HA) environments. The controller manages all subsequent models in each environment.
Charm: The definition of a service, including its metadata, dependencies with other services, required packages, and application management logic. It contains all the operational knowledge of deploying a Kubernetes cluster. Included charm examples are kubernetes-core, easy-rsa, kibana etc.
Kubectl: The command line configuration tool for Kubernetes.
Kubelet: A service that runs on nodes and reads the container manifests to ensure the defined containers are started and running.
Machine: A physical node that can be either bare metal nodes or virtual machines provided by a cloud.
Master: The machine that controls Kubernetes nodes and where all task assignments originate. This controls all the nodes in Kubernetes.
Model—A collection of charms and their relationships that define a deployment. This includes machines and units. A controller can host multiple models.
Node—These are machines that perform the requested or assigned tasks. The Kubernetes master controls them.
Pod—A group of one or more containers deployed to a single node. All containers in a pod share an IP address, IPC (interprocess communication), hostname, and other resources. This ensures you can move containers around the cluster more easily.
Replication controller—This controls how many identical copies of a pod you can have in a cluster.
Service—This decouples work definitions from the pods. Kubernetes service proxies automatically get service requests to the right pod—no matter where it moves to in the cluster or even if it’s been replaced.
Unit—A given instance of a service. These may or may not use up a whole machine, and may be collocated on the same machine. So, for example, you might have a kubernetes-worker, and file beat, and top beat units running on a single machine, but they are three distinct units of different services.
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