The following is a summary of some of the core concepts of Kubernetes as required to write an operator. Before we begin, Kubernetes is a portable, extensible, open-source platform for managing containerized workloads and services. It is often a strategic decision for any company because it decouples the application from the hosts so that the same application can work elsewhere with minimal disruption to its use.
An operator is a way of automating the deployment of an application on the Kubernetes cluster. It is written with the help of template source code generated by a tool called the operator-sdk. The tool builds three components – custom resource, apis and controllers. The custom resources are usually declarative definition of Kubernetes resources required by the application and its grouping as suited for the deployment of the application. The api is for the custom service required to deploy the application and the controller watches for this service.
Kubernetes does not limit the type of applications that are supported. It provides building blocks to the application. Containers only help isolate modules of the application into well defined boundaries that can run in with operating system level virtualization.
Kubernetes exposes a set of APIs that are used internally by the command line tool called kubectl. It is also used externally by other applications. This API follows the regular REST convention and is also versioned with path qualifiers such as v1, v1alpha1 or v1beta1 – the latter are used with extensions to the APIs.
Kubernetes supports Imperative commands, imperative object configuration, and declarative object configuration. These are different approaches to manage objects. The first approach operates on live objects and is recommended for development environment. The latter two are configurations that operate on individual files or a set of files and these are better suited for production environments.
Namespaces seclude names of resources. They can even be nested within one another. They provide a means to divide resources between multiple users.
Most Kubernetes resources such as pods, services, replication, controllers, and others are in some namespaces. However, low level resources such as nodes and persistent volumes are not in any namespace.
Kubernetes control plane communication is bidirectional between the cluster to its master and vice-versa. The master hosts an apiserver that is configured to listen for remote connections. The apiserver reaches out to the kubelets to fetch logs, attach to running pods, and provide the port-forwarding functionality. The apiserver manages nodes, pods and services.
An operator is a way of automating the deployment of an application on the Kubernetes cluster. It is written with the help of template source code generated by a tool called the operator-sdk. The tool builds three components – custom resource, apis and controllers. The custom resources are usually declarative definition of Kubernetes resources required by the application and its grouping as suited for the deployment of the application. The api is for the custom service required to deploy the application and the controller watches for this service.
Kubernetes does not limit the type of applications that are supported. It provides building blocks to the application. Containers only help isolate modules of the application into well defined boundaries that can run in with operating system level virtualization.
Kubernetes exposes a set of APIs that are used internally by the command line tool called kubectl. It is also used externally by other applications. This API follows the regular REST convention and is also versioned with path qualifiers such as v1, v1alpha1 or v1beta1 – the latter are used with extensions to the APIs.
Kubernetes supports Imperative commands, imperative object configuration, and declarative object configuration. These are different approaches to manage objects. The first approach operates on live objects and is recommended for development environment. The latter two are configurations that operate on individual files or a set of files and these are better suited for production environments.
Namespaces seclude names of resources. They can even be nested within one another. They provide a means to divide resources between multiple users.
Most Kubernetes resources such as pods, services, replication, controllers, and others are in some namespaces. However, low level resources such as nodes and persistent volumes are not in any namespace.
Kubernetes control plane communication is bidirectional between the cluster to its master and vice-versa. The master hosts an apiserver that is configured to listen for remote connections. The apiserver reaches out to the kubelets to fetch logs, attach to running pods, and provide the port-forwarding functionality. The apiserver manages nodes, pods and services.
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