Kubernetes cluster expansion

1. Please explain the basic concepts and principles of Kubernetes cluster expansion.

Basic concepts and principles of Kubernetes cluster expansion:

Kubernetes is an open source container orchestration platform used to automate the deployment, scaling and management of application containers. In Kubernetes, cluster expansion refers to increasing the computing resources (such as CPU, memory, etc.) in the cluster to meet the growing needs of applications.

The principle of Kubernetes cluster expansion is mainly based on the following aspects:

1. Autoscaling: Kubernetes uses the autoscaling function to dynamically adjust the number of Pods in the cluster based on the actual load of the application. When the load increases, Kubernetes will automatically create new Pods to meet demand; when the load decreases, Kubernetes will automatically delete redundant Pods to save resources.

2. Horizontal Pod Autoscaling (HPA): HPA is an automatic scaling strategy of Kubernetes, which automatically adjusts the number of Pods based on custom indicators (such as CPU usage, memory usage, etc.). HPA allows users to set target values and tolerance ranges to keep application performance stable when load fluctuates.

3. Node Pool: In a Kubernetes cluster, nodes can be divided into different pools, and the nodes in each pool have different resource specifications (such as CPU, memory, etc.). By allocating node pools with different resource specifications to applications, vertical and horizontal expansion of the cluster can be achieved.

4. Scheduler: The Kubernetes scheduler is responsible for allocating Pods to appropriate nodes to run. When the cluster is expanded, the scheduler will schedule Pods to nodes with sufficient resources based on the resource status of the nodes and the needs of the application.

In short, the basic concept and principle of Kubernetes cluster expansion is to dynamically adjust the computing resources in the cluster according to the actual load of the application through mechanisms such as automatic scaling, horizontal expansion, node pools, and schedulers to meet the growing needs of the application.

2. How to add new nodes to the Kubernetes cluster?

To add a new node to the Kubernetes cluster, you can follow the following steps:

1. Prepare a new node: You need a new server or virtual machine and make sure it meets the requirements for a Kubernetes node. This includes running an operating system that supports Kubernetes (such as Ubuntu, CentOS, etc.), and configuring basic environments such as networks and firewalls.

2. Install Docker and kubelet: Kubernetes nodes require Docker and kubelet to be installed because Kubernetes uses container technology to deploy and run applications. The specific installation steps depend on the operating system and version you are using. You can find the corresponding guide in the official Kubernetes documentation.

3. Generate kubeconfig file: The kubeconfig file contains the connection information and credentials for the Kubernetes cluster. It is used for authorization and authentication.

4. Obtain the master’s join token: This step usually uses the command kubeadm token create --print-join-command --ttl=0 (where –ttl=0 means that the token will never expire, and the default is not to add this parameter Expires in 24 hours). After the execution is completed, the following command will be automatically generated.

5. Install Kubernetes related software packages and configure kubelet on the new node.

6. Use the kubeadm command on the master node of the cluster to add the new node to the cluster. The specific command is kubeadm join :<7777 --token --discovery-token-ca-cert-hash sha256:.

7. Use the kubeadm command on the new node to join it to the cluster. The specific command is kubeadm join :7777 --token --discovery-token-ca-cert-hash sha256:.

3. Please describe how Horizontal Pod Autoscaling (HPA) works in Kubernetes?

In Kubernetes, Horizontal Pod Autoscaler (HPA) is a built-in feature that enables automatic scaling of Pods based on CPU usage. This automated process is called “horizontal scaling” and means deploying more Pods in response to increased load.

HPA periodically detects the Pod’s CPU usage based on the duration defined by the kube-controller-manager service startup parameter –horizontal-pod-autoscaler-sync-period (default is 30 seconds) on the Master Node (heapster needs to be installed in advance).

Its implementation is a control loop with a period specified by the controller manager’s –horizontal-pod-autoscaler-sync-period parameter (the default value is 15 seconds). Each cycle, it will obtain the resource objects of all ReplicationController, ReplicaSet, Deployment and StatefulSet in all named spaces, and then calculate according to the target CPU utilization set by the user to obtain the current number of replicas that each Pod should run. Finally Update the number of copies of the corresponding Pod through the API Server to achieve automatic expansion and contraction.

4. How to add a new replica set in a Kubernetes cluster?

To add a new replica set to a Kubernetes cluster, you can use the kubectl command line tool. Here are the specific steps:

1. Create a new YAML file that defines the new replica set. For example, create a file named replicaset.yaml with the following content:

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: my-replicaset
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
      - name: my-container
        image: my-image

This YAML file defines a replica set named my-replicaset, which will run 3 Pods named my-container, which will use an image named my-image.

2. Apply this YAML file using the kubectl apply command to create a new replica set:

kubectl apply -f replicaset.yaml

This will create a new replica set in the Kubernetes cluster and run the corresponding Pods as defined in the YAML file.

5. Please explain how Vertical Pod Autoscaling (VPA) works in Kubernetes?

Vertical Pod Autoscaling (VPA) in Kubernetes is a powerful extension that automatically adjusts Pod resource limits, such as CPU and memory. Its core function is that it can automatically set CPU and memory requests according to the resource usage of the container, and then perform appropriate scheduling on the node to provide appropriate resources for each Pod.

It is worth noting that when a Pod’s resource usage approaches its limit, the VPA will kick in and consider increasing its resources. For example, if the memory usage of a Pod reaches 98Mi and the memory limit is 100Mi, VPA may increase the memory limit of the Pod to avoid OOM (out of memory).

In addition, VPA can also optimize resources and control costs. It can dynamically adjust the resource limits of Pods according to the actual resource requirements of the application, avoiding over-allocation of resources, thereby saving resources and reducing costs. At the same time, it can also prevent applications from experiencing performance issues or crashing due to insufficient resources.

However, one thing to note when using VPA is that this component is not yet production-ready, and you need to understand the impact of resource regulation on the application before using it.

6. How to add new services to the Kubernetes cluster?

To add a new service to the Kubernetes cluster, you can perform the following steps:

1. Create a new YAML file that will be used to describe the details of the new service. In this file, some main properties need to be defined, including ApiVersion, Kind, Metadata and Spec. ApiVersion is the version number of the Kubernetes API. For services, its value is usually “v1”; Kind is the resource type. For services, its value is “Service”; Metadata includes the name, namespace and other information of the service; Spec is The most important part, it defines various attributes of the service, including the selector, which will point to the backend Pod; type, which can be ClusterIP, NodePort or LoadBalancer; ports, which defines the service exposure port.

2. Save and name this YAML file, for example, “my-service.yaml”.

3. Use the kubectl command line tool to apply this YAML file to create a new service in the Kubernetes cluster. The specific command format is as follows:

kubectl apply -f my-service.yaml

Among them, “my-service.yaml” is the name of the YAML file you saved in the previous step. It should be noted that if the specified name already exists in the current namespace, the new service will replace the old service.

7. Please explain the role and use of the Deployment resource object in Kubernetes.

In Kubernetes, Deployment is an important resource object, mainly used to describe and control the deployment of one or more Pods. Its main function is to define and manage multi-copy applications (i.e., multiple replica Pods) to ensure service continuity and stability.

Compared with Replication Controller, Deployment provides more complete functions and is simpler and more convenient to use. For example, if a Pod fails, the corresponding service will also be suspended. At this time, the Pod can be automatically restored through Deployment to ensure the continuity and stability of the service. In addition, when the definition of a Pod changes, the Deployment is also responsible for rolling updates (Rolling Update) to each copy to implement version control and updates of the application.

When creating and managing Deployment resource objects, we can use the kubectl command line tool, which is one of the most commonly used tools in Kubernetes. In this way, we can more easily manage and deploy applications, achieve high availability and elastic system architecture, and improve application reliability and scalability.

8. How to add a new ConfigMap in the Kubernetes cluster?

To add a new ConfigMap in a Kubernetes cluster, you can use the kubectl create configmap command. The specific operations are as follows:

1. Open a terminal.
2. Enter the following command, replacing with the namespace in which the ConfigMap is to be created, with the name of the ConfigMap to be created, and Replace = with key-value pairs, separated by spaces.

kubectl create configmap <namespace>/<configmap-name> --from-literal=<key>=<value>

For example, to create a ConfigMap named my-configmap in the namespace named my-namespace, which contains a key-value pair key1=value1, you can execute the following commands:

kubectl create configmap my-namespace/my-configmap --from-literal=key1=value1

3. If you need to add multiple key-value pairs, you can separate them with commas:

kubectl create configmap <namespace>/<configmap-name> --from-literal=<key1>=<value1>,<key2>=<value2>,...

For example:

kubectl create configmap my-namespace/my-configmap --from-literal=key1=value1,key2=value2,key3=value3

9. Please explain the role and purpose of the StatefulSet resource object in Kubernetes.

StatefulSet is a workload API object for managing stateful applications in Kubernetes. Its main functions and uses can be summarized as follows:

1. Management of stateful applications: StatefulSet is mainly used to manage stateful applications. Its Pod has a sticky and unique identity. This identification is based on the unique sequential index assigned to each Pod by the StatefulSet controller. This identity makes the Pod persistent in the cluster. Even if the Pod is scheduled to a different node in the cluster or is destroyed and restarted, the identifier will still be retained.

2. Stable network identification: Through Headless Service, StatefulSet creates a fixed and unchanging DNS domain name for each Pod it controls, which serves as the network identification of the Pod within the cluster. This provides stable network access for stateful applications.

3. Orderly deployment and deletion: StatefulSet supports orderly deployment and deletion of Pod instances. This means that when you expand or shrink a StatefulSet, the related Pods will start or stop in a predetermined order.

4. Support for persistent storage volumes: Pods in StatefulSet use stable persistent storage volumes, which are implemented through PV/PVC. When a Pod is deleted, the storage volume related to the StatefulSet will not be deleted by default, ensuring data security.

5. Automatic update policy: Starting from Kubernetes version 1.7, the StatefulSet controller supports automatic updates. The update strategy is determined by the spec.updateStrategy field of the StatefulSet API object and can be used to update the container image, resource requests and restrictions, labels and annotations of the Pod in a StatefulSet.

To sum up, StatefulSet provides powerful management and deployment capabilities for stateful applications, ensuring high availability of applications and persistence of data.

10. How to add a new Ingress resource to the Kubernetes cluster?

In a Kubernetes cluster, the Ingress resource is a key API object, mainly used to manage external access to internal services in the cluster. It provides users with HTTP and HTTPS traffic routing methods. At the same time, the rules defined on the Ingress resource are responsible for controlling the routing of these traffic. Ingress is a set of rules that authorizes inbound connections to reach cluster services. It mainly provides seven-layer load balancing capabilities.

When using the Ingress resource, one thing that must be noted is that creating the Ingress resource alone cannot achieve external access to the internal services of the cluster. You must have an ingress controller to meet the requirements of Ingress. Common ingress controllers include ingress-nginx and so on.

As for how to add a new Ingress resource to the Kubernetes cluster, you can do it in the following two ways: one is to operate through the console, and the other is to operate through the Kubectl command line tool. No matter which method is used, you need to create a YAML file of the Ingress resource first, describing the Ingress rules in detail, including externally accessible URLs, load balancing, SSL, name-based virtual host and other settings. Then, apply this YAML file to the Kubernetes cluster and a new Ingress resource will be created.

11. Please explain the role and purpose of the ServiceAccount resource object in Kubernetes.

In Kubernetes, the ServiceAccount resource object plays a very important role and is mainly used to manage service accounts in the cluster. Its core functions mainly include the following aspects:

1. Identity authentication and authorization: ServiceAccount provides identities for processes running in the cluster. In this way, these processes can access the Kubernetes API Server. When these processes need to access other resources, the API Server checks their identity information to confirm whether they have permission to operate.

2. Pod association: The process running in the Pod can obtain the corresponding identity credentials by mounting the ServiceAccount Secret. This is usually accomplished by adding the serviceAccountName field to the Pod definition.

3. RBAC (Role-Based Access Control): ServiceAccount supports role-based access control, which means that different ServiceAccounts can be assigned different roles to control their access to Kubernetes resources.

4. Secret management: ServiceAccount can also be used to manage Secrets, such as storing sensitive information such as passwords and OAuth tokens. This Secret can only be accessed by the Pod associated with it, thereby enhancing security.

In general, ServiceAccount is an important tool for security and permission management in Kubernetes. It ensures that only appropriately authorized processes can access cluster resources, and can effectively protect sensitive information from unauthorized access.

12. How to add a new Secret to the Kubernetes cluster?

In a Kubernetes cluster, Secret is a resource object mainly used to store sensitive information such as passwords and tokens. These sensitive information are stored using Base64 encoding, but Base64 is only an encoding method and does not contain the key, so it is not secure.

To add a new Secret in a Kubernetes cluster, you can follow these steps:

1. Use the kubectl create secret command to create a new Secret. For example, to save the username and password to a newly created Secret, you can use the following command:

kubectl create secret generic my-secret --from-file=username.txt --from-file=password.txt

This command will create two key-value pairs from the files username.txt and password.txt and store them in a file named my-secretSecret.

2. You can also update the contents of an existing Secret object by editing it. To edit a Secret, execute the following command:

kubectl edit secrets <secret-name>

Please replace with the name of the secret you want to edit.

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: my-storageclass
provisioner: example.com/my-provisioner
parameters:
  type: nfs
  nfs: "path=/tmp/data"
reclaimPolicy: Retain
allowVolumeExpansion: true
mountOptions: ["hard", "intr", "rsize=10G", "wsize=10G", "noatime"]

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: mycustomresources.example.com
spec:
  group: example.com
  versions:
    - name: v1
      served: true
      storage: true
      Schema:
        openAPIV3Schema:
          type: object
          properties:
            spec:
              type: object
              properties:
                name:
                  type: string
    additionalPrinterColumns:
    - name: Age
      type: string
      description: The age of the custom resource instance
      jsonPath: .metadata.creationTimestamp
  scope: Namespaced
  names:
    plural: mycustomresources
    singular: mycustomresource
    kind: MyCustomResource
    shortNames:
    -mcr

kubectl apply -f mycrd.yaml

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: my-network-policy
spec:
  podSelector:
    matchLabels:
      app: my-app
  policyTypes:
  - Ingress
  - Egress
  ingress:
  - from:
    -ipBlock:
        cidr: 10.0.0.0/8
    ports:
    - protocol: TCP
      port: 80
  egress:
  - to:
    -ipBlock:
        cidr: 10.0.0.0/8
    ports:
    - protocol: TCP
      port: 80

# Get the yaml file from the official repository
curl https://github.com/kubernetes-sigs/metrics-server/releases/download/v0.6.1/components.yaml -o metrics-server.yaml
# Replace image
sed -i 's/k8s.gcr.io\/metrics-server\/metrics:v0.3.7/k8s.gcr.io\/metrics-server\/metrics:v0.3.7/' metrics-server.yaml

kubectl apply -f metrics-server.yaml

apiVersion: autoscaling/v2beta2
kind: VerticalPodAutoscaler
metadata:
  name: example-vpa
spec:
  targetRef:
    apiVersion: "apps/v1"
    Kind: Deployment
    name: example-deployment
  updatePolicy:
    type: Off
  resourcePolicy:
    cpu:
      containerResourcePercentage: 50
    memory:
      containerMemoryPercentage: 50