Compute
Elastic Cloud Server
Huawei Cloud Flexus
Bare Metal Server
Auto Scaling
Image Management Service
Dedicated Host
FunctionGraph
Cloud Phone Host
Huawei Cloud EulerOS
Networking
Virtual Private Cloud
Elastic IP
Elastic Load Balance
NAT Gateway
Direct Connect
Virtual Private Network
VPC Endpoint
Cloud Connect
Enterprise Router
Enterprise Switch
Global Accelerator
Management & Governance
Cloud Eye
Identity and Access Management
Cloud Trace Service
Resource Formation Service
Tag Management Service
Log Tank Service
Config
OneAccess
Resource Access Manager
Simple Message Notification
Application Performance Management
Application Operations Management
Organizations
Optimization Advisor
IAM Identity Center
Cloud Operations Center
Resource Governance Center
Migration
Server Migration Service
Object Storage Migration Service
Cloud Data Migration
Migration Center
Cloud Ecosystem
KooGallery
Partner Center
User Support
My Account
Billing Center
Cost Center
Resource Center
Enterprise Management
Service Tickets
HUAWEI CLOUD (International) FAQs
ICP Filing
Support Plans
My Credentials
Customer Operation Capabilities
Partner Support Plans
Professional Services
Analytics
MapReduce Service
Data Lake Insight
CloudTable Service
Cloud Search Service
Data Lake Visualization
Data Ingestion Service
GaussDB(DWS)
DataArts Studio
Data Lake Factory
DataArts Lake Formation
IoT
IoT Device Access
Others
Product Pricing Details
System Permissions
Console Quick Start
Common FAQs
Instructions for Associating with a HUAWEI CLOUD Partner
Message Center
Security & Compliance
Security Technologies and Applications
Web Application Firewall
Host Security Service
Cloud Firewall
SecMaster
Anti-DDoS Service
Data Encryption Workshop
Database Security Service
Cloud Bastion Host
Data Security Center
Cloud Certificate Manager
Edge Security
Managed Threat Detection
Blockchain
Blockchain Service
Web3 Node Engine Service
Media Services
Media Processing Center
Video On Demand
Live
SparkRTC
MetaStudio
Storage
Object Storage Service
Elastic Volume Service
Cloud Backup and Recovery
Storage Disaster Recovery Service
Scalable File Service Turbo
Scalable File Service
Volume Backup Service
Cloud Server Backup Service
Data Express Service
Dedicated Distributed Storage Service
Containers
Cloud Container Engine
SoftWare Repository for Container
Application Service Mesh
Ubiquitous Cloud Native Service
Cloud Container Instance
Databases
Relational Database Service
Document Database Service
Data Admin Service
Data Replication Service
GeminiDB
GaussDB
Distributed Database Middleware
Database and Application Migration UGO
TaurusDB
Middleware
Distributed Cache Service
API Gateway
Distributed Message Service for Kafka
Distributed Message Service for RabbitMQ
Distributed Message Service for RocketMQ
Cloud Service Engine
Multi-Site High Availability Service
EventGrid
Dedicated Cloud
Dedicated Computing Cluster
Business Applications
Workspace
ROMA Connect
Message & SMS
Domain Name Service
Edge Data Center Management
Meeting
AI
Face Recognition Service
Graph Engine Service
Content Moderation
Image Recognition
Optical Character Recognition
ModelArts
ImageSearch
Conversational Bot Service
Speech Interaction Service
Huawei HiLens
Video Intelligent Analysis Service
Developer Tools
SDK Developer Guide
API Request Signing Guide
Terraform
Koo Command Line Interface
Content Delivery & Edge Computing
Content Delivery Network
Intelligent EdgeFabric
CloudPond
Intelligent EdgeCloud
Solutions
SAP Cloud
High Performance Computing
Developer Services
ServiceStage
CodeArts
CodeArts PerfTest
CodeArts Req
CodeArts Pipeline
CodeArts Build
CodeArts Deploy
CodeArts Artifact
CodeArts TestPlan
CodeArts Check
CodeArts Repo
Cloud Application Engine
MacroVerse aPaaS
KooMessage
KooPhone
KooDrive

Deployment

Updated on 2024-11-01 GMT+08:00

Pod describes pod, which is the smallest and simplest unit in the Kubernetes object model that you create or deploy. However, a pod is designed to be a one-off entity. A pod can be evicted (when node resources are insufficient) and disappears as the cluster node fails. Kubernetes provides controllers to manage pods. Controllers can create and manage multiple pods, and provide replica management, rolling upgrade, and self-healing capabilities. The most commonly used is Deployment.

A Deployment can contain one or more pod replicas. Each pod replica has the same role. Therefore, the system automatically distributes requests to multiple pod replicas of a Deployment.

A Deployment integrates a lot of functions, including online deployment, rolling upgrade, replica creation, and restoration of online jobs. To some extent, Deployments can be used to realize unattended rollout, which greatly reduces communication difficulties and operation risks in the rollout process.

Creating a Deployment

In the following example, a Deployment named nginx is created, and two pod replicas are created from the nginx:latest image. Each pod replica occupies 500m and 1024Mi memory.

apiVersion: apps/v1      # Note the difference from that of pods. It is apps/v1 instead of v1 for a Deployment.
kind: Deployment         # The resource type is Deployment.
metadata:
  name: nginx            # Name of the Deployment
spec:
  replicas: 2            # Number of pod replicas. The Deployment ensures that two pod replicas are running.
  selector:              # Label Selector
    matchLabels:
      app: nginx
  template:              # Definition of a pod, which is used to create pods. It is also known as pod template.
    metadata:
      labels:
        app: nginx
    spec:
      volumes:
        - name: cci-sfs-test                     # SFS volume name
          persistentVolumeClaim:
            claimName: cci-sfs-test
      containers:
      - image: nginx:latest
        name: container-0
        resources:
          limits:
            cpu: 500m
            memory: 1024Mi
          requests:
            cpu: 500m
            memory: 1024Mi
        volumeMounts:
          - name: cci-sfs-test
            mountPath: /tmp/sfs0/krlp2k8j        # SFS volume's mount path in a container
      imagePullSecrets:           # Secret used to pull the image, which must be imagepull-secret.
      - name: imagepull-secret

In this definition, the name of the Deployment is nginx, and spec.replicas defines the number of pods. That is, the Deployment controls two pods. spec.selector is a label selector, indicating that the Deployment selects the pod whose label is app=nginx. spec.template is the definition of the pod and is the same as that defined in Pod.

Save the definition of the Deployment to deployment.yaml and use kubectl to create the Deployment.

Run the kubectl get command to view the Deployment and the pods. The value of DESIRED is 2, indicating that the Deployment desires two pods. The value of CURRENT is 2, indicating that there are two pods. The value of AVAILABLE is 2, indicating that two pods are available.

$ kubectl create -f deployment.yaml -n $namespace_name 

$ kubectl get deployment -n $namespace_name
NAME      DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
nginx     2         2         2            2           8s

How Does the Deployment Control Pods?

Continue to query pods, as shown below.

$ kubectl get pods -n $namespace_name
NAME                     READY     STATUS    RESTARTS   AGE
nginx-7f98958cdf-tdmqk   1/1       Running   0          13s
nginx-7f98958cdf-txckx   1/1       Running   0          13s

If you delete a pod, a new pod is immediately created, as shown below. As mentioned above, the Deployment ensures that there are two pods running. If a pod is deleted, the Deployment creates another pod. If a pod crashes or is faulty, the Deployment automatically restarts the pod.

$ kubectl delete pod nginx-7f98958cdf-txckx -n $namespace_name

$ kubectl get pods -n $namespace_name 
NAME                     READY     STATUS    RESTARTS   AGE
nginx-7f98958cdf-tdmqk   1/1       Running   0          21s
nginx-7f98958cdf-tesqr   1/1       Running   0          21s

There are two pods, nginx-7f98958cdf-tdmqk and nginx-7f98958cdf-tesqr, in which nginx is the name of the Deployment, and -7f98958cdf-tdmqk and -7f98958cdf-tesqr are the suffixes randomly generated by Kubernetes.

You may notice that the first part of the two suffixes is the same, that is, 7f98958cdf. This is because the Deployment does not control the pod directly, but through a controller named ReplicaSet. You can run the following command to query the ReplicaSet, in which rs is the abbreviation of ReplicaSet.

$ kubectl get rs -n $namespace_name
NAME               DESIRED   CURRENT   READY     AGE
nginx-7f98958cdf   3         3         3         1m

The name of the ReplicaSet is nginx-7f98958cdf, and the suffix -7f98958cdf is generated randomly.

Figure 1 shows how the Deployment controls the pod via the ReplicaSet.

Figure 1 Control flow

If you run the kubectl describe command to view the details of the Deployment, you can see the ReplicaSet. As shown below, you can see a line NewReplicaSet: nginx-7f98958cdf (2/2 replicas created). In events, the number of pods of the ReplicaSet is scaled out to 2. In practice, you may not operate ReplicaSet directly, but understanding that a Deployment controls a pod by controlling a ReplicaSet helps you locate problems.

$ kubectl describe deploy nginx -n $namespace_name
Name:                   nginx
Namespace:              default
CreationTimestamp:      Sun, 16 Dec 2018 19:21:58 +0800
Labels:                 app=nginx

...

NewReplicaSet:   nginx-7f98958cdf (2/2 replicas created)
Events:
  Type    Reason             Age   From                   Message
  ----    ------             ----  ----                   -------
  Normal  ScalingReplicaSet  5m    deployment-controller  Scaled up replica set nginx-7f98958cdf to 2

Upgrade

In actual applications, upgrade is a common operation. A Deployment can easily support application upgrade.

You can set different upgrade policies for a Deployment:

  • RollingUpdate: Gradually create new pods and delete old pods). This is the default policy.
  • Recreate: Delete the current pods and then create new pods.

The Deployment upgrade can be in declarative mode. That is, you only need to modify the YAML definition of the Deployment. For example, you can run the kubectl edit command to change the Deployment image to nginx:alpine. After the modification, query the ReplicaSet and pod, a new ReplicaSet is created, and the pod is recreated.

$ kubectl edit deploy nginx -n $namespace_name

$ kubectl get rs -n $namespace_name
NAME               DESIRED   CURRENT   READY     AGE
nginx-6f9f58dffd   2         2         2         1m
nginx-7f98958cdf   0         0         0         48m

$ kubectl get pods -n $namespace_name
NAME                     READY     STATUS    RESTARTS   AGE
nginx-6f9f58dffd-tdmqk   1/1       Running   0          21s
nginx-6f9f58dffd-tesqr   1/1       Running   0          21s

The Deployment can use the maxSurge and maxUnavailable parameters to control the proportion of pods to be recreated during the upgrade. This is useful in many scenarios. The configuration is as follows:

spec:
  strategy:
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0
    type: RollingUpdate
  • maxSurge: specifies the percent of pods that can exist over spec.replicas in the Deployment. The default value is 25%. For example, if spec.replicas is set to 4, no more than five pods can exist during the upgrade, and the upgrade step is 1. The absolute number is calculated from the percentage by rounding up. The value can also be set to an absolute number.
  • maxUnavailable: specifies the percent of pods that can be unavailable during the update. The default value is 25%. For example, if spec.replicas is set to 4, there must be at least three pods during the upgrade, so the deleting step is 1. The value can also be set to an absolute number.

In the preceding example, the value of spec.replicas is 2. Suppose both maxSurge and maxUnavailable are the default value 25%, maxSurge allows a maximum of three pods to exist (2 * 1.25 = 2.5, rounded up to 3), and maxUnavailable does not allow unavailable pods (2 * 0.75 = 1.5, rounded up to 2). As a result, two pods are running during the upgrade. Each time a new pod is created, an old pod is deleted, until all pods are new.

Rollback

Rollback is to roll an application back to the earlier version when a fault occurs during the upgrade. A Deployment can be easily rolled back to the earlier version.

For example, if the upgraded image is faulty, you can run the kubectl rollout undo command to roll back.

$ kubectl rollout undo deployment nginx -n $namespace_name
deployment "nginx" rolled back

A Deployment can be easily rolled back because a Deployment uses a ReplicaSet to control a pod. After the upgrade, the ReplicaSet still exists. The Deployment is rolled back by recreating the pod using the ReplicaSet. The number of ReplicaSets stored in a Deployment can be restricted by the revisionHistoryLimit parameter. The default value is 10.

We use cookies to improve our site and your experience. By continuing to browse our site you accept our cookie policy. Find out more

Feedback

Feedback

Feedback

0/500

Selected Content

Submit selected content with the feedback