Kubernetes StatefulSet in KubeSphere

As a workload API object, a Kubernetes StatefulSet is used to manage stateful applications. It is responsible for the deploying, scaling of a set of Pods, and guarantees the ordering and uniqueness of these Pods.

Like a Deployment, a StatefulSet manages Pods that are based on an identical container specification. Unlike a Deployment, a StatefulSet maintains a sticky identity for each of their Pods. These Pods are created from the same specification, but are not interchangeable: each has a persistent identifier that it maintains across any rescheduling.

If you want to use storage volumes to provide persistence for your workload, you can use a StatefulSet as part of the solution. Although individual Pods in a StatefulSet are susceptible to failure, the persistent Pod identifiers make it easier to match existing volumes to the new Pods that replace any that have failed.

StatefulSets are valuable for applications that require one or more of the following.

• Stable, unique network identifiers.
• Stable, persistent storage.
• Ordered, graceful deployment, and scaling.
• Ordered, automated rolling updates.

For more information, see the official documentation of Kubernetes.

Prerequisites

You need to create a workspace, a project and a user (project-regular). The user must be invited to the project with the role of operator. For more information, see Create Workspaces, Projects, Users and Roles.

Create a Kubernetes StatefulSet

In KubeSphere, a Headless service is also created when you create a StatefulSet. You can find the headless service in Services under Application Workloads in a project.

Step 1: Open the dashboard

Log in to the console as project-regular. Go to Application Workloads of a project, select Workloads, and click Create under the StatefulSets tab.

Step 2: Enter basic information

Specify a name for the StatefulSet (for example, demo-stateful), select a project, and click Next.

Step 3: Set a Pod

1. Before you set an image, define the number of replicated Pods in Pod Replicas by clicking or , which is indicated by the .spec.replicas field in the manifest file.

   Tip

   You can see the StatefulSet manifest file in YAML format by enabling Edit YAML in the upper-right corner. KubeSphere allows you to edit the manifest file directly to create a StatefulSet. Alternatively, you can follow the steps below to create a StatefulSet via the dashboard.

2. Click Add Container.

3. Enter an image name from public Docker Hub or from a private repository you specified. For example, enter nginx in the search box and press Enter.

   Note

   • Remember to press Enter on your keyboard after you enter an image name in the search box.
   • If you want to use your private image repository, you should create an Image Registry Secret first in Secrets under Configuration.

4. Set requests and limits for CPU and memory resources based on your needs. For more information, see Resource Request and Resource Limit in Container Image Settings.

5. Click Use Default Ports for Port Settings or you can customize Protocol, Name and Container Port.

6. Select a policy for image pulling from the drop-down list. For more information, see Image Pull Policy in Container Image Settings.

7. For other settings (Health Check, Start Command, Environment Variables, Container Security Context and Synchronize Host Timezone), you can configure them on the dashboard as well. For more information, see detailed explanations of these properties in Pod Settings. When you finish, click √ in the lower-right corner to continue.

8. Select an update strategy from the drop-down menu. It is recommended you choose Rolling Update. For more information, see Update Strategy.

9. Select a Pod scheduling rule. For more information, see Pod Scheduling Rules.

10. Click Next to continue when you finish setting the container image.

Step 4: Mount volumes

StatefulSets can use the volume template, but you must create it in Storage in advance. For more information about volumes, visit Volumes. When you finish, click Next to continue.

Step 5: Configure advanced settings

You can set a policy for node scheduling and add StatefulSet metadata in this section. When you finish, click Create to complete the whole process of creating a StatefulSet.

• Select Nodes

  Assign Pod replicas to run on specified nodes. It is specified in the field nodeSelector.

• Add Metadata

  Additional metadata settings for resources such as Labels and Annotations.

Check Kubernetes StatefulSet Details

Details page

1. After a StatefulSet is created, it will be displayed in the list. You can click on the right to select options from the menu to modify your StatefulSet.

   • Edit Information: View and edit the basic information.
   • Edit YAML: View, upload, download, or update the YAML file.
   • Re-create: Re-create the StatefulSet.
   • Delete: Delete the StatefulSet.

2. Click the name of the StatefulSet and you can go to its details page.

3. Click More to display what operations about this StatefulSet you can do.

   • Roll Back: Select the revision to roll back.
   • Edit Service: Set the port to expose the container image and the service port.
   • Edit Settings: Configure update strategies, containers and volumes.
   • Edit YAML: View, upload, download, or update the YAML file.
   • Re-create: Re-create this StatefulSet.
   • Delete: Delete the StatefulSet, and return to the StatefulSet list page.

4. Click the Resource Status tab to view the port and Pod information of a StatefulSet.

   • Replica Status: Click or to increase or decrease the number of Pod replicas.

   • Pods

     • The Pod list provides detailed information of the Pod (status, node, Pod IP and resource usage).
     • You can view the container information by clicking a Pod item.
     • Click the container log icon to view output logs of the container.
     • You can view the Pod details page by clicking the Pod name.

Revision records

After the resource template of workload is changed, a new log will be generated and Pods will be rescheduled for a version update. The latest 10 versions will be saved by default. You can implement a redeployment based on the change log.

Metadata

Click the Metadata tab to view the labels and annotations of the StatefulSet.

Monitoring

1. Click the Monitoring tab to view the CPU usage, memory usage, outbound traffic, and inbound traffic of the StatefulSet.

2. Click the drop-down menu in the upper-right corner to customize the time range and sampling interval.

3. Click / in the upper-right corner to start/stop automatic data refreshing.

4. Click in the upper-right corner to manually refresh the data.

Environment variables

Click the Environment Variables tab to view the environment variables of the StatefulSet.

Events

Click the Events tab to view the events of the StatefulSet.

Thanks for the feedback. If you have a specific question about how to use KubeSphere, ask it on Slack. Open an issue in the GitHub repo if you want to report a problem or suggest an improvement.