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Kubernetes, K8s for short, is an open source application used to manage containerized applications on multiple hosts in the cloud platform. The goal of Kubernetes is to make the deployment of containerized applications simple and efficient (powerful). Kubernetes provides a mechanism for application deployment, planning, update and maintenance.

Kubernetes supports not only Docker, but also Rocket, another container technology.

With Kubernetes, you can: automate container deployment and replication; expand or shrink container size at any time; organize containers into groups and provide load balancing between containers; easily upgrade new versions of application containers; provide container resilience, replace it if the container fails, and so on.

Introduction to Kubernetes Core Concepts

Pod- container group

Pod is the basic operating unit of Kubernetes, specifying multiple associated containers (with invocation dependency) to form a Pod. Pod contains containers that run on the same Minion (Worker Node), and Pod is designed to allow multiple containers to share network addresses and file systems in a Pod.

Deployment- deployment

Deployment is available only in recent versions, and deployment represents a user's update to the K8s cluster. Deployment is an API object that is broader than the RS application pattern, and you can create, update, or scroll upgrade a new service.

Job- task

Job is the API object that K8s uses to control batch tasks. The main difference between the batch business and the long-term servo business is that the batch business runs from beginning to end, while the long-term servo business runs forever without the user stopping. The Pod managed by Job automatically exits when the task is successfully completed according to the settings of the user, and the flag for successful completion varies according to different spec.completions policies.

DaemonSet- background support service set

The core of long-term server and batch service is business application, the core focus of background support service is the node (physical machine or virtual machine) in K8s cluster, and the node may be all cluster nodes or some specific nodes selected by nodeSelector. Typical background support services include, storing, logging, and monitoring services that support K8s cluster operation on each node.

PetSet- stateful Service set

K8s released the PetSet function of the Alpha version in version 1.3. the main purpose of RC and RS is to control the provision of stateless services, and the name of the Pod it controls is randomly set. The name function of the Pod in PetSet is used to correlate the state corresponding to the Pod.

Replication Controller- replication Controller

RC is the earliest API object in K8s cluster to ensure the high availability of Pod. By monitoring the running Pod to ensure that a specified number of Pod replicas are running in the cluster. It is wiser to run Pod through RC than to run Pod directly, and RC ensures the number of Pod.

Replica Set- replica set

RS is a new generation of RC, which provides the same high availability, and RS can support more kinds of matching patterns. Replica sets are generally not used alone, but as status parameters of Deployment.

Service- service

RC, RS and Deployment only guarantee the number of microservice Pod supporting services, but do not solve how to access these services. Stable provision of services requires service discovery and load balancing capabilities.

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