Detailed explanation of Kubernetes architecture and components

1. Introduction to Kubernetes

1 What is Kubernetes

Kubernetes is an open source container orchestration system by Google, a platform for automating the deployment, scaling, and management of containerized applications. Kubernetes makes full use of cloud computing and containerization technologies, which can greatly simplify the development, deployment and operation of applications.

2 Advantages of Kubernetes

The advantages of Kubernetes mainly include the following points:

1. High availability : Kubernetes can run across multiple geographic locations and cloud platforms, ensuring high availability and business continuity.
2. Easy to expand : Kubernetes can be expanded by adding/removing nodes to better meet business needs, and it can also automate load and traffic management.
3. Convenient deployment management : Kubernetes can help users easily create and manage container images, deploy container applications, and release resources.
4. Automation : Because Kubernetes is an automated platform, it can automatically manage tasks such as load balancing, scaling, rolling updates, and health checks, freeing up more time to focus on core business.
5. Extensible ecosystem : Kubernetes has rich plug-ins, applications, tools, and community support, which can provide users with a richer and extensible ecosystem.

3 Application Scenarios of Kubernetes

Kubernetes is mainly applicable to the following scenarios:

1. Cloud-native applications: Kubernetes can be used to easily deploy and manage cloud-native applications, improving development efficiency and application reliability.
2. DevOps: Kubernetes can help development teams deploy applications to production environments faster and more securely.
3. Distributed computing and distributed data storage and processing: Using Kubernetes can help users easily build distributed computing and data storage clusters, thereby improving the efficiency of big data processing.
4. Container construction and online deployment management: Container images can be easily built and managed through Kubernetes, and deployed and managed online.

2. Kubernetes architecture

1 Kubernetes architecture overview

Kubernetes is a distributed system, and its core is to distribute containerized applications to a group of machines and manage their life cycle, so that applications can run efficiently and stably. The architecture of Kubernetes supports the deployment of a containerized application on one node, and also supports its deployment across multiple nodes and multiple machines.

2 Introduction to Kubernetes Architecture Components

2.1 Control Panel Components

The control plane component is the core of the Kubernetes system and is used to manage the entire system. These include components such as kube-apiserver, etcd, kube-controller-manager, and kube-scheduler. These components interact through the API Server to handle the work in the cluster.

2.2 API Server

API Server is a RESTful API provided by Kubernetes and is the central component of the Kubernetes system. It is the front-end component of the Kubernetes control plane that handles all requests in the cluster and forwards them to the correct components so they can work together.

2.3 etcd

etcd is a data storage system adopted by the Kubernetes system, which is used to store configuration and status information in the cluster. etcd is a highly available distributed key-value storage system that ensures consistent state throughout the system.

2.4 kubelet

Kubelet is an agent program running on each machine, and its task is to create, schedule and maintain Pods. The kubelet is also responsible for interacting with the Control Plane to receive tasks and jobs from the cluster.

2.5 to proxy

kube-proxy is a network proxy program running on each node, which is responsible for providing service discovery and load balancing functions for Pod objects. kube-proxy routes requests from a service port to the corresponding Pod by passing the request and routing the request to the correct Pod according to the rules.

2.6 CNI plugins

The CNI (Container Networking Interface) plugin is a plugin system in Kubernetes for managing container networking. The CNI plugin provides support for Kubernetes and can assign IP addresses and networks to each Pod object managed by Kubernetes. The use of CNI plugins makes the Kubernetes network model very flexible.

2.7 Container runtime

The container runtime is a component used to run containers in Kubernetes, and it supports multiple container runtimes such as Docker and rkt. Kubernetes provides a container runtime interface, making it easy to switch to other container runtimes. The container runtime supports the management of operations such as starting, stopping, and suspending containers, and realizes resource management and isolation at the container level.

3. Kubernetes application management

In Kubernetes, applications are managed through models such as Pod, Deployment, StatefulSet, DaemonSet, and Job. This article will introduce the concepts, usage methods, and precautions of these models to help you better understand and use Kubernetes.

1 Pod overview

1.1 Pod concept

Pod is the most basic scheduling unit in Kubernetes and the smallest unit of containerization. It consists of one or more closely connected containers that share the same IP address and network namespace, and can share access to the same storage volumes and resources on the host. Pod is the basic object for scheduling and management of Kubernetes. A Pod instance will only run once on a node.

1.2 Pod life cycle

The life cycle of a Pod instance in Kubernetes includes the following stages:

1. Creation phase: The Kubernetes API server creates and initializes Pods, creates containers according to the container specification in Pods, and sets the state for Pods.
2. Running phase: After the container in the Pod is initialized, it starts running. During the running process, Kubernetes will monitor the running status of the container, such as whether the container is running normally, or whether the container has exited.
3. Container exception: If a container in a Pod terminates abnormally, Kubernetes will decide whether to restart the container or terminate the Pod instance according to the defined container restart policy.
4. Deletion phase: Pod instances can be deleted through the Kubernetes API when the Pod is no longer needed.

2 Introduction to the Kubernetes model

Kubernetes provides a variety of models for deploying and managing applications, including Deployment, StatefulSet, DaemonSet, and Job, etc.

2.1 Deployment model

Deployment is one of the most commonly used models in Kubernetes for deploying and updating applications. Deployment can be managed using ReplicaSet and Pod to achieve horizontal scaling and upgrading of applications. To create a Deployment, you need to define a YAML file describing the Deployment. The following is a simple Nginx deployment example:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 3 
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80

This YAML file defines a Deployment object named nginx-deployment that will use the nginx:1.7.9 image to run a container named nginx. The Deployment will start 3 Pod processes, and each Pod process will contain an nginx container.

2.2 StatefulSet model

StatefulSet is used to deploy stateful applications. It can provide orderly Pod management and service discovery, and ensure the stability of applications among multiple Pod instances. The following is an example YAML file for a StatefulSet:

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: my-statefulset
spec:
  selector:
    matchLabels:
      app: my-app
  serviceName: my-service
  replicas: 3
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
      - name: my-pod
        image: my-image
        ports:
        - containerPort: 8181

A StatefulSet object named my-statefulset is defined in the above YAML file, which uses the image my-image to run a container named my-pod. This StatefulSet object will start 3 Pod processes and generate a unique stable identifier for each Pod process.

2.3 DaemonSet model

DaemonSet is used to deploy daemons running on each node in the cluster. DaemonSet can ensure that there is a Pod instance on each node, so as to realize node-level service discovery and monitoring. The following is an example YAML file for a DaemonSet:

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: fluentd
spec:
  selector:
    matchLabels:
      app: fluentd
  template:
    metadata:
      labels:
        app: fluentd
    spec:
      containers:
      - name: fluentd
        image: fluentd:v1.0.2
        ports:
        - containerPort: 24224

A DaemonSet object named fluentd is defined in the above YAML file, which uses the fluentd:v1.0.2 image to run a container named fluentd. A Pod process runs on each node, and each Pod process contains a fluentd container

2.4 Job model

Job is used to periodically execute batch tasks to implement one-time tasks and scheduled tasks in Kubernetes. The following is an example YAML file for a Job:

apiVersion: batch/v1
kind: Job
metadata:
  name: my-job
spec:
  template:
    metadata:
      name: my-job
    spec:
      restartPolicy: OnFailure
      containers:
      - name: my-job-container
        image: my-image
        command: ["/bin/sh", "-c", "echo hello; sleep 30; echo world"]
  backoffLimit: 2

A Job object named my-job is defined in the above YAML file, which uses the image my-image to run a container named my-job-container. The container will execute the commandecho hello; sleep 30; echo world

3 Kubernetes configuration management

Kubernetes provides two mechanisms, ConfigMap and Secret, for injecting configuration information and sensitive data. When using these mechanisms, the application's configuration and secrets can be stored centrally in Kubernetes for easy management and updates

3.1 ConfigMap

ConfigMap can be used to inject application-related configuration information into Pods in the form of configuration files. ConfigMap configuration information can be shared by multiple Pods, which facilitates centralized configuration management and update maintenance.

Here is an example YAML file for a ConfigMap:

apiVersion: v1
kind: ConfigMap
metadata:
  name: my-config
data:
  database.properties: |
    database.url=jdbc:mysql://127.0.0.1:3306/test
    database.username=test
    database.password=password
  server.properties: |
    server.port=8080
    server.timeout=300

In the above YAML file, a ConfigMap object named my-config is defined, and a database.properties file and a server.properties file are defined

3.2 Secret

Secrets can be used to inject sensitive information into Pods in encrypted form. Secret, like ConfigMap, can also manage the configuration information shared by multiple Pods

The following is an example of a Secret YAML file:

apiVersion: v1
kind: Secret
metadata:
  name: my-secret
type: Opaque
stringData:
  username: admin
  password: myPassword

In the above YAML file, a Secret object named my-secret is defined, and a username and password are defined. In actual use, the data in the Secret will be encrypted and stored in etcd, decrypted and injected into the container when the Pod is initialized.

4. Kubernetes network model

The network is a crucial part of Kubernetes. It is the basis for Kubernetes to achieve load balancing and service discovery across multiple nodes. In Kubernetes, there are mainly three network models: single-node Docker bridge mode, CNI mode and Service mode.

1 Kubernetes Network Overview

Kubernetes supports multiple networking models but they all need to work together to ensure network availability and performance. In Kubernetes, the network is mainly used in the following three aspects:

• Network communication between pods
• Network communication between container and host
• External access to services provided by the Kubernetes cluster

In order to realize these network functions, Kubernetes needs to configure some network components and solutions on each node.

2 Kubernetes network scheme

There are a variety of network solutions in Kubernetes, and different solutions can be selected according to different needs

2.1 Single node Docker bridge mode

Single-node Docker bridge mode is one of the simplest and most common networking scenarios in Kubernetes. In this scheme, each Docker container has its own IP address, and Kubernetes uses a bridge named Docker0 to connect these IP addresses together to achieve communication between the container and the host

2.2 CNI mode

CNI mode is a more advanced networking scheme in Kubernetes that uses a standard interface called Container Network Interface (CNI) to manage container networking. CNI can enable various network plug-ins in Kubernetes, such as Flannel, Calico and Canal, etc., to achieve different network functions

2.3 Service mode

Service mode is a network solution used in Kubernetes to provide load balancing and service discovery for containers. In Kubernetes, Service is an abstraction of a set of Pods, which use a unified DNS name and virtual IP address. Kubernetes implements service discovery and load balancing of applications through Service

3 Kubernetes network management tools

Network management is an important task in Kubernetes and requires specialized tools for management and maintenance

3.1 kube-router

kube-router is a complete network solution in Kubernetes, which provides solutions for Pod network, Service network and external network. kube-router also provides full IPv6 support, which can provide support for IPv6 networking in Kubernetes

3.2 Cilia

Cilium is a networking and security solution for Kubernetes that provides high-performance network I/O services using Linux kernel technology. Cilium also provides complete security policies, security plug-ins and security logs, which can enhance the security and reliability of Kubernetes networks

5. Kubernetes storage management

Storage is another important part of Kubernetes, which can provide reliable persistent storage and data management. In Kubernetes, there are two main storage models: Volume and PersistentVolume/Claim

1 Kubernetes Storage Overview

Kubernetes' storage model is designed for containerized applications, and it provides a variety of pluggable storage backends, such as local storage, NFS storage, and cloud storage. Kubernetes abstracts storage resources into PersistentVolume (PV) and PersistentVolumeClaim (PVC).

2 Kubernetes storage model

2.1 Volume

Volume is the basic component used to provide persistent storage for Pod in Kubernetes, and it can store data in the container to Pod. Kubernetes supports multiple Volume types, such as EmptyDir, HostPath, NFS, and GlusterFS, and you can choose different Volume types according to different needs

2.2 PersistentVolume/Claim

PersistentVolume (PV) is a component used to describe physical storage resources in Kubernetes, which provides an abstraction layer to separate storage resources from applications. PersistentVolumeClaim (PVC) is a component used to request storage resources from Kubernetes. It can bind Pod and PersistentVolume to provide persistent storage for containers

53 Kubernetes storage management tools

Storage management in Kubernetes is mission critical and requires specialized tools for management and maintenance

3.1 Ceph

Ceph is an open source distributed storage system that provides high availability and high scalability storage services. In Kubernetes, Ceph cluster can be integrated with Kubernetes to provide a reliable storage solution for containers

3.2 GlusterFS

GlusterFS is an open source distributed file system that aggregates storage devices on multiple servers into a large storage pool to provide high availability and high scalability storage services. In Kubernetes, GlusterFS cluster can be integrated with Kubernetes to provide a reliable storage solution for containers

6. Kubernetes Security Policy

1 Kubernetes Security Overview

The security of applications and data is paramount in Kubernetes. Kubernetes provides several security mechanisms and tools to help protect and isolate applications and data. Kubernetes security mainly includes identity authentication, authorization, access control, network security, and secret management.

2 Kubernetes security model

The security model in Kubernetes covers many aspects, including Namespace, ServiceAccount and RBAC etc.

2.1 Namespace Namespace

Namespace is a resource classification mechanism in Kubernetes, which isolates a group of resources for resource management and permission control. Each namespace has its own list of resources, and resources between namespaces are isolated from each other. Some namespaces are predefined in Kubernetes, such as default, kube-system, etc. Users can also customize namespaces

2.2 ServiceAccount

ServiceAccount is a mechanism for authentication and authorization in Kubernetes, which provides default authentication information for Pods. In Kubernetes, each Pod has its own ServiceAccount, which can provide Pod with different authentication and authorization strategies. Kubernetes also provides various authentication and authorization mechanisms, such as OAuth, Webhook, etc.

2.3 RBAC

RBAC is a mechanism for authorization in Kubernetes that assigns permissions to specific users or groups of users and enforces authorization policies across the Kubernetes cluster. RBAC can define roles (Role) and role binding (RoleBinding) to grant permissions to specific users or user groups and restrict their access to specific resources in the cluster.

7. Kubernetes High Availability Solution

1 Kubernetes High Availability Overview

In Kubernetes, high availability is an important prerequisite for reliable deployment and management of applications. By deploying a highly available Kubernetes cluster, functions such as fault tolerance, load balancing, and automatic failover can be achieved

2 Kubernetes High Availability Solution

2.1 Multiple control nodes

The control node (Control Plane) in Kubernetes is one of the key components used to manage the entire Kubernetes cluster, including kube-apiserver, kube-controller-manager, and kube-scheduler. In order to achieve high availability, multiple control nodes can be deployed in the Kubernetes cluster for fault tolerance and load balancing

2.2 High availability based on etcd cluster

etcd is a key component in Kubernetes for storing cluster state, which provides data storage and sharing functions for the entire Kubernetes cluster. In order to achieve high availability, data redundancy and automatic failover can be achieved by deploying an etcd cluster.

2.3 High availability based on virtual IP

In Kubernetes, virtual IP (VIP) can be used to achieve high availability. By using VIPs, multiple Kubernetes nodes can be formed into a redundant cluster for features such as fault tolerance and automatic failover.

3 Kubernetes High Availability Tools

3.1 kubeadm cluster installation tool

Kubeadm is an official cluster installation tool provided by Kubernetes. It can quickly deploy a highly available Kubernetes cluster and provides a variety of pluggable components and plug-ins to expand and customize the Kubernetes cluster.

3.2 kubespray cluster installation tool

kubespray is an open source Kubernetes cluster installation tool developed based on Ansible automation tools and official Kubernetes guides. Kubespray can quickly deploy a highly available Kubernetes cluster, and provides a variety of pluggable components and plug-ins to expand and customize the Kubernetes cluster.

Eight, Kubernetes troubleshooting

Troubleshooting in Kubernetes is an important part of system maintenance and debugging. This article will introduce Kubernetes troubleshooting from three aspects: overview, analysis of common fault causes, and troubleshooting techniques.

1 Kubernetes Troubleshooting Overview

Troubleshooting Kubernetes typically involves multiple components and technologies, including networks, nodes, and pods. When troubleshooting, you need to locate the scope and specific cause of the fault first, and then take corresponding measures to eliminate it. Different troubleshooting techniques and tools are usually required for different types of failures

2 Cause Analysis of Common Kubernetes Faults

2.1 Network failure

Network issues are one of the common causes of failure in Kubernetes. When containers in a cluster cannot communicate with other containers or with the external network, it may be due to network configuration issues, network failures, or cross-host communication errors, etc. Ways to troubleshoot network failures include checking network topology, configuration, and routing, and checking network policies and security groups in Kubernetes, among others.

# 示例：检查 Pod IP 和服务 IP 是否冲突
apiVersion: v1
kind: Pod
metadata:
  name: test-pod
spec:
  containers:
  - name: test-container
    image: nginx
    ports:
    - containerPort: 80
---
apiVersion: v1
kind: Service
metadata:
  name: test-service
spec:
  selector:
    app: test
  ports:
  - name: http
    port: 80
    targetPort: 80
  type: ClusterIP

2.2 Node abnormality

Kubernetes node abnormalities are another common cause of failure. When a node is not functioning or accessible properly, it may cause problems such as pod startup failure, container inoperability, or data loss. Methods for troubleshooting node anomalies include checking node status, hardware failures, resource utilization, and container logs, etc.

# 示例：查看节点状态和资源利用率
$ kubectl get nodes
$ kubectl describe node <nodename>
$ kubectl top node

2.3 Pod exceptions

Pod exceptions in Kubernetes usually include container crashes, image pull failures, and insufficient container resources. When Pods fail to start or execute commands properly, it can lead to problems such as service unavailability, data loss, or heavy load. Ways to resolve Pod exceptions include checking container status, Pod lifecycle, container resource quotas and logs, etc.

# 示例：查看 Pod 状态和容器日志
$ kubectl get pods
$ kubectl describe pod <podname>
$ kubectl logs <podname> -c <containername>

3 Kubernetes Troubleshooting Tips

When troubleshooting Kubernetes faults, you need to master some skills and tools to improve troubleshooting efficiency. These include:

• Use kubectl commands to query resource status, get logs, and execute troubleshooting commands.
• Install monitoring and diagnostic tools such as Prometheus, Grafana, sysdig, etc. in nodes and containers.
• Use Kubernetes Dashboard or other resource management tools to view and manage cluster resources.
• Record the troubleshooting process and results, and update relevant documents and materials in a timely manner.