Introduction to the K8s introductory series

? Kubernetes Introduction
1. Background information
The rapid development of cloud computing
-IaaS
-PaaS
-SaaS
Docker technology leaps and bounds
-Build once, run everywhere
-Fast and lightweight container
-Complete ecological environment
2. What is Kubernetes
Kubernetes (k8s) is Google open-source container cluster Management system (Google internal: Borg). On the basis of Docker technology, a series of complete functions such as deployment operation, resource scheduling, service discovery and dynamic scaling are provided for containerized applications, which improves the convenience of large-scale container cluster management.
Kubernetes Advantages:
-Container Orchestration
-Lightweight
-Open Source
-Elastic expansion
-Load Balancing

? The core concept of kubernetes
1.Pod
A combination of several related containers that run on node nodes. The containers contained within the Pod run on the same host, using the same network namespace, IP address, and port to pass through localhost. Pods are the smallest unit of kurbernetes for Creation, dispatch, and management, providing a higher level of abstraction than containers, making deployment and management more flexible. A pod can contain a container or multiple related containers.
2.Replication Controller
The Replication Controller manages a copy of the pod to ensure that a specified number of pod copies exist in the cluster. If the number of replicas in the cluster is greater than the specified number, the number of extra containers that are outside the specified number is stopped, and conversely, containers with fewer than a specified number are started and the quantity is guaranteed to be constant. Replication Controller is the core of elastic scaling, dynamic expansion and rolling upgrades.
3.Service
The service defines the logical set of pods and the policies that access the collection, which is an abstraction of the real service. The service provides a unified access portal for services and service proxies and discovery mechanisms that users do not need to know how the background pod is running.
4.Label
Any API object in Kubernetes is identified by a label, and the essence of the label is a series of k/v key-value pairs. The label is the basis for running the replication controller and service, and they are associated with the pod running on node with a label.
5.Node
node is the service node (also known as Agent or Minion) that runs the pod in the Kubernetes cluster schema. node is a unit of Kubernetes cluster operation that hosts the running of the allocated pod and is the host on which the pod runs.

? Kubernetes Architecture and Components
Architecture:

　　
Master-Slave distributed architecture, Master/node
-Service grouping, small cluster, multi-cluster
-Service grouping, large cluster, single cluster
Component:
The Kubernetes master control component, which schedules and manages the entire system (cluster), contains the following components:
1.Kubernetes API Server
As the entrance of the kubernetes system, it encapsulates the additions and deletions of the core objects, which are provided to external customers and internal component calls in the RESTful API interface mode. Maintained rest objects are persisted to ETCD storage.
2.Kubernetes Scheduler
Node selection (that is, allocating machines) for the newly created Pod is responsible for resource scheduling of the cluster. The components are drawn away and can be easily replaced by other schedulers.
3.Kubernetes Controller
Responsible for the implementation of various controllers, has now provided a number of controllers to ensure the normal operation of Kubernetes.

-Replication Controller
Manage and maintain replication controllers, correlate replication controllers and pods, and ensure that the number of replicas defined by the replication controller is consistent with the number of pods actually running.
-Node Controller
Manage and maintain node, periodically check node's health status, and identify node nodes that are (fail | invalidated).
-Namespace Controller
Manage maintenance namespace, periodically clean up invalid namespace, including API objects under NAMESAPCE, such as pod, service, etc.
-Service Controller
Manage maintenance service, provide load and service agent.
-Endpoints Controller
Manage maintenance endpoints, correlate service and pod, create endpoints as service backend, update endpoints in real time when pod changes.
-Service Account Controller
Manage Maintenance service account, create a default service account for each namespace, and create service account Secret for the service account.
-Persistent Volume Controller
Manage Maintenance Persistent Volume and persistent Volume Claim, assign persistent Volume for new Claim persistent Volume to bind, persistent for release Volume performs cleanup reclamation.
-Daemon Set Controller
Management Maintenance Daemon Set, responsible for creating the daemon pod, to ensure that the specified node on the normal running daemon pod.
-Deployment Controller
Manage maintenance deployment, associate Deployment and replication controllers, and ensure that you run a specified number of pods. Control implements updates to the replication controller and pod when deployment is updated.
-Job Controller
Manage Maintenance jobs, create a one-time task pod for JOD, and ensure that the number of tasks completed by job completion is specified
-Pod Autoscaler Controller
The pod is automatically scaled, the monitoring data is acquired periodically, the strategy is matched, and the pod scaling action is performed when the condition is met.

Kubernetes node runs the management business container, which contains the following components:
1.Kubelet
In charge of the control container, Kubelet receives the pod creation request from the Kubernetes API server, starts and stops the container, monitors the container's operational status and reports to Kubernetes API server.
2.Kubernetes Proxy
Responsible for creating the proxy service for pod, Kubernetes Proxy obtains all service information from Kubernetes API server and creates proxy service based on service information, enabling service-to-Pod request routing and forwarding. In order to achieve kubernetes level of virtual forwarding network.
3.Docker
Node needs to run the container service.

Introduction to the K8s introductory series