You can deploy stateful applications in the Container Service for Kubernetes (ACK) console. This topic describes how to deploy a stateful application from an image. A stateful NGINX application is used as an example. The features of StatefulSets are also demonstrated in this topic.

Prerequisites

Before you deploy a stateful application from an image, perform the following steps:

Background information

StatefulSets provide the following features:
Feature Description
Pod consistency Pod consistency guarantees that pods are started and terminated in the specified order and also guarantees the consistency of networks. The consistency of pods is determined by the configurations of the pods, regardless of the node to which a pod is scheduled.
Stable and persistent storage VolumeClaimTemplate allows you to mount a persistent volume (PV) to each pod. The mounted PVs are not deleted after you delete or scale in the replicated pods.
Stable network identifiers Each pod in a StatefulSet derives its hostname from the name of the StatefulSet and the ordinal of the pod. The pattern for the hostname is StatefulSet name-pod ordinal.
Stable orders For a StatefulSet with N replicated pods, each pod is assigned an integer ordinal from 0 to N-1. The ordinals assigned to pods within the StatefulSet are unique.

Procedure

  1. Log on to the ACK console.
  2. In the left-side navigation pane of the ACK console, click Clusters.
  3. On the Clusters page, find the cluster that you want to manage and click the name of the cluster or click Details in the Actions column. The details page of the cluster appears.
  4. In the left-side navigation pane of the details page, choose Workloads > Deployments.
  5. Click the StatefulSets tab. On the StatefulSets tab, click Create from Image.
  6. On the Basic Information wizard page, configure the basic settings.

    In this example, the Type parameter is set to StatefulSets to deploy a stateful application.

    Parameter Description
    Name The name of the application.
    Namespace The namespace where you want to deploy the application. The default namespace is automatically selected. You can select another namespace.
    Replicas The number of pods that are provisioned for the application.
    Type The type of application. You can select Deployments, StatefulSets, Jobs, Cron Jobs, or DaemonSets.
    Label Add a label to the application. The label is used to identify the application.
    Annotations Add an annotation to the application.
    Synchronize Timezone Specify whether to synchronize the time zone between nodes and containers.
  7. Click Next to proceed to the Container wizard page.
  8. Configure the containers.
    Note At the top of the Container wizard page, click Add Container to provision more containers for the application.
    The following parameters are required to configure the containers.
    • GeneralGeneral settings
      Parameter Description
      Image Name
      • To use a Docker image or an image from Container Registry (ACR), click Select Image. In the dialog box that appears, select an image and click OK. In this example, an NGINX image is selected. On the Search tab, select Docker Images from the drop-down list, enter NGINX in the search bar, and then click Search.
        • Alibaba Cloud Container Registry: On the Alibaba Cloud Container Registry tab, you can select an image from ACR. You must specify the region and ACR instance of the image. For more information about ACR, see What is Container Registry Enterprise Edition?.
          Note On the Alibaba Cloud Container Registry tab, you can enter an image name to search for an image in ACR.
        • Docker Official Images: On the Docker Official Images tab, you can select a Docker image.
        • Favorite Images: On the Favorite Images tab, you can select a Docker image that you have specified as one of your favorite images.
        • Search: On the Search tab, you can select Alibaba Cloud Images from the drop-down list and specify a region to search for an image in ACR. You can also select Docker Images from the drop-down list and search for a Docker image.
      • You can also enter the address of a private registry. The registry address must be in the domainname/namespace/imagename:tag format.

      Image Version

      • Click Select Image Version and select an image version. If you do not specify an image version, the latest image version is used.
      • You can select the following image pull policies:
        • ifNotPresent: If the image you want to pull is found in the region where the cluster is deployed, the local image is used. Otherwise, ACK pulls the image from the corresponding repository.
        • Always: ACK pulls the image from the repository each time the application is deployed or expanded.
        • Never: ACK uses only local images.
        Note If you select Image Pull Policy, no image pull policy is applied for the deployment of the application.
      • To pull the image without a secret, click Set Image Pull Secret to set a secret for pulling images. For more information, see Use aliyun-acr-credential-helper to pull images without a password.
      Resource Limit You can specify an upper limit for the CPU, memory, and ephemeral storage resources that the container can consume. This prevents the container from occupying an excessive amount of resources. The CPU resource is measured in millicores (one thousandth of one core). The memory resource is measured in MiB. The ephemeral storage resource is measured in GiB.
      Required Resources The amount of CPU and memory resources that are reserved for this application. These resources are exclusive to the container. This prevents the application from becoming unavailable when other Services or processes occupy these resources.
      Container Start Parameter
      • stdin: specifies that start parameters defined in the console are sent to the Linux system.
      • tty: specifies that start parameters defined in a virtual terminal are sent to the console.
      Privileged Container
      • If you select Privileged Container, privileged=true is set for the container. This indicates that the privilege mode is enabled.
      • If you do not select Privileged Container, privileged=false is set for the container. This indicates that the privilege mode is disabled.
      Init Container If you select Init Container, an init container is created. An init container provides tools to manage pods. For more information, see Init Containers.
    • Optional:Ports
      Specify the container port.
      • Name: Enter a name for the container port.
      • Container Port: the container port that you want to open. Enter a port number from 1 to 65535.
      • Protocol: Select TCP or UDP.
    • Optional:Environments
      You can set environment variables in key-value pairs for pods. Environment variables are used to apply pod configurations to containers. For more information, see Pod variables.
      • Type: the type of environment variable. You can select Custom, ConfigMaps, Secret, or Value/ValueFrom. If you select ConfigMaps or Secret as the type of environment variable, all values in the selected ConfigMaps or Secret are passed to the container environment variables. In this example, Secret is selected.

        Select Secret from the Type drop-down list and select a Secret from the Value/ValueFrom drop-down list. All values in the selected Secret are passed to the environment variable.

        In this case, the YAML file used to deploy the application contains the settings that reference all values in the specified Secret.

      • Variable Key: Specify the key of the environment variable.
      • Value/ValueFrom: Specify the value that is referenced by the environment variable.
    • Optional:Health Check

      Health check settings include liveness and readiness probes. Liveness probes determine when to restart the container. Readiness probes indicate whether the container is ready to accept network traffic. For more information about health checks, see Configure Liveness, Readiness, and Startup Probes.

      Request type Description
      HTTP Sends an HTTP GET request to the container. You can set the following parameters:
      • Protocol: HTTP or HTTPS.
      • Path: the requested path on the server.
      • Port: the container port that you want to open. Enter a port number from 1 to 65535.
      • HTTP Header: the custom headers in the HTTP request. Duplicate headers are allowed. You can specify the HTTP headers in key-value pairs.
      • Initial Delay (s): the initialDelaySeconds field in the YAML file. This field specifies the amount of time (in seconds) that the system must wait before it can send the first probe to a launched container. Default value: 3.
      • Period (s): the periodSeconds field in the YAML file. This field specifies the interval (in seconds) at which probes are sent. Default value: 10. Minimum value: 1.
      • Timeout (s): the timeoutSeconds field in the YAML file. This field specifies the timeout period (in seconds) of probes. Default value: 1. Minimum value: 1.
      • Healthy Threshold: the minimum number of times that an unhealthy container must consecutively pass health checks before it is considered healthy. Default value: 1. Minimum value: 1. For liveness probes, this parameter must be set to 1.
      • Unhealthy Threshold: the minimum number of times that a healthy container must consecutively fail health checks before it is considered unhealthy. Default value: 3. Minimum value: 1.
      TCP Sends a TCP socket to the container. Kubelet attempts to open the socket on the specified port. If the connection can be established, the container is considered healthy. Otherwise, the container is considered unhealthy. Supported parameters include:
      • Port: the container port that you want to open. Enter a port number from 1 to 65535.
      • Initial Delay (s): the initialDelaySeconds field in the YAML file. This field specifies the time period (in seconds) that the system must wait before it can send the first probe to a launched container. Default value: 15.
      • Period (s): the periodSeconds field in the YAML file. This field specifies the interval (in seconds) at which probes are sent. Default value: 10. Minimum value: 1.
      • Timeout (s): the timeoutSeconds field in the YAML file. This field specifies the timeout period (in seconds) of probes. Default value: 1. Minimum value: 1.
      • Healthy Threshold: the minimum number of times that an unhealthy container must consecutively pass health checks before it is considered healthy. Default value: 1. Minimum value: 1. For liveness probes, this parameter must be set to 1.
      • Unhealthy Threshold: the minimum number of times that a healthy container must consecutively fail health checks before it is considered unhealthy. Default value: 3. Minimum value: 1.
      Command Runs a probe command in the container to check the health status of the container. Supported parameters include:
      • Command: the probe command that is run to check the health status of the container.
      • Initial Delay (s): the initialDelaySeconds field in the YAML file. This field specifies the time period (in seconds) that the system must wait before it can send the first probe to a launched container. Default value: 5.
      • Period (s): the periodSeconds field in the YAML file. This field specifies the interval (in seconds) at which probes are sent. Default value: 10. Minimum value: 1.
      • Timeout (s): the timeoutSeconds field in the YAML file. This field specifies the timeout period (in seconds) of probes. Default value: 1. Minimum value: 1.
      • Healthy Threshold: the minimum number of times that an unhealthy container must consecutively pass health checks before it is considered healthy. Default value: 1. Minimum value: 1. For liveness probes, this parameter must be set to 1.
      • Unhealthy Threshold: the minimum number of times that a healthy container must consecutively fail health checks before it is considered unhealthy. Default value: 3. Minimum value: 1.
    • Lifecycle

      You can set the following parameters to configure the lifecycle of the container: Start, Post Start, and Pre Stop. For more information, see Configure the lifecycle of a container.

      • Start: Set the command and parameter that take effect before the container starts.
      • Post Start: Set the command that takes effect after the container starts.
      • Pre Stop: Set the command that takes effect before the container stops.
    • Optional:Volume
      You can mount local storage volumes and persistent volume claims (PVCs) to the container.
      • Local Storage: You can select HostPath, ConfigMap, Secret, or EmptyDir. The specified storage volume is mounted to a path in the container. For more information, see Volumes.
      • PVC: Select Cloud Storage.
      In this example, a PVC named disk-ssd is mounted to the /tmp path of the container.Configure the volume
    • Optional:Log
      Configure Log Service. You can specify collection configurations and add tags.
      Notice Make sure that the Log Service agent is installed in the cluster.
      Parameter Description
      Collection Configuration Logstore: Create a Logstore in Log Service to store the collected log data.
      Log Path in Container: Specify stdout or a path to collect log data.
      • stdout: specifies that the stdout files are collected.
      • Text Logs: specifies that the log files in the specified path of the container are collected. In this example, /var/log/nginx is specified as the path. Wildcard characters can be used in the path.
      Custom Tag You can also add tags. Tags are added to the logs of the container when the logs are collected. Log data with tags is easier to aggregate and filter.
  9. Set the preceding parameters based on your business requirements and click Next.
  10. Optional:Configure advanced settings.
    • Access Control
      Note

      You can configure the following access control settings based on your business requirements:

      • Internal applications: For applications that run inside the cluster, you can create a Service of the ClusterIP or NodePort type to enable internal communication.
      • External applications: For applications that are open to the Internet, you can configure access control by using one of the following methods:
        • Create a LoadBalancer Service that uses a Server Load Balancer (SLB) instance and use the Service to expose your application to the Internet.
        • Create an Ingress and use the Ingress to expose your application to the Internet. For more information, see Ingress.

      You can also specify how the backend pods are exposed to the Internet. In this example, a ClusterIP Service and an Ingress are created to expose the NGINX application to the Internet.

      Parameter Description
      Services Click Create on the right side of Service. In the Create Service dialog box, set the parameters. For more information about the parameters that are required to create a Service, see Manage Services. Cluster IP is selected in this example.
      Ingresses Click Create on the right side of Ingresses. In the Create dialog box, set the parameters. For more information about the parameters that are required to create an Ingress, see Ingress configurations.
      Note When you deploy an application from an image, you can create an Ingress for only one Service. In this example, the name of a virtual host is used as the test domain name. You must add the following entry to the hosts file to map the domain name to the IP address of the Ingress. In practical scenarios, use a domain name that has obtained an Internet Content Provider (ICP) number.
      101.37.224.146   foo.bar.com    # The IP address of the Ingress.
      You can find the created Service and Ingress in the Access Control section. Click Update or Delete to modify the settings.Update or delete the Ingress
    • Scaling
      In the Scaling section, specify whether to enable HPA and CronHPA. Horizontal Pad Autoscaler (HPA) enables the application to run at different load levels.
      • HPA can automatically scale the number of pods in an ACK cluster based on the CPU and memory usage.
        Note To enable HPA, you must configure resources that can be scaled for containers. Otherwise, HPA does not take effect.
        Parameter Description
        Metric Select CPU Usage or Memory Usage. The selected resource type must be the same as the one that you specified in the Required Resources field.
        Condition Specify the resource usage threshold. HPA triggers scaling activities when the threshold is exceeded.
        Max. Replicas Specify the maximum number of replicated pods to which the application can be scaled.
        Min. Replicas Specify the minimum number of replicated pods that must run.
      • CronHPA can scale an ACK cluster at a scheduled time. For more information about CronHPA, see Create CronHPA jobs.
    • Scheduling
      You can set the following parameters: Update Method, Node Affinity, Pod Affinity, Pod Anti Affinity, and Toleration. For more information, see Affinity and anti-affinity.
      Note During pod scheduling, the labels of a node and a pod determine the affinities of the node and pod. You can configure node affinity and pod affinity by selecting preset labels or by manually adding labels.
      Parameter Description
      Update Method

      Select Rolling Update or OnDelete. For more information, see Deployments.

      Node Affinity Add labels to worker nodes to set Node Affinity.
      Node affinity supports required and preferred rules, and various operators, such as In, NotIn, Exists, DoesNotExist, Gt, and Lt.
      • Required: Specify the rules that must be matched for a pod to be scheduled to a node. Required rules correspond to the requiredDuringSchedulingIgnoredDuringExecution affinity, which is conceptually similar to NodeSelector. In this example, pods can be scheduled to only worker nodes with specified labels. You can create more than one required rule. However, only one required rule must be met.
      • Preferred: Specify the rules that are preferred to match. Preferred rules correspond to the preferredDuringSchedulingIgnoredDuringExecution affinity. In this example, the scheduler attempts to avoid scheduling a pod to a node that matches the preferred rules. You can set node weights in preferred rules. If multiple nodes match the preferred rules, the pod is preferably scheduled to the node with the highest weight. You can create more than one preferred rule. All preferred rules must be matched before a pod can be scheduled to a preferred node.
      Pod Affinity Pod affinity specifies that a pod is scheduled to a node in the same topological domain if the node runs a pod that matches the affinity rules. For example, you can use pod affinity to deploy Services that communicate with each other to the same topological domain, such as a host. This reduces the network latency between these Services.
      You can enforce pod affinity by using the labels of the pods that run on a node. Pod affinity supports required and preferred rules, and the following operators: In, NotIn, Exists, and DoesNotExist.
      • Required: Specify the rules that must be matched for a pod to be scheduled to a node. Required rules correspond to the requiredDuringSchedulingIgnoredDuringExecution affinity. A node must match the required rules before a pod can be scheduled to the node.
        • Namespace: Specify a namespace rule. Pod affinity is scoped to namespaces because it is enforced based on the labels of pods.
        • Topological Domain: Set the topologyKey. This specifies the key for the node label that the system uses to denote the topological domain. For example, if you set the parameter to kubernetes.io/hostname, topologies are determined by nodes. If you set the parameter to beta.kubernetes.io/os, topologies are determined by the operating systems of nodes.
        • Selector: Click Add to add pod labels.
        • View Applications: Click View Applications, and set the namespace and application in the dialog box that appears. You can view the pod labels on the selected application and add the labels as selectors.
        • Required Rules: Specify labels of existing applications, operators, and label values. In this example, the required rule specifies that the application to be created is scheduled to a host that runs applications with the app:nginx label.
      • Preferred: Specify the rules that are preferred to match. Preferred rules correspond to the preferredDuringSchedulingIgnoredDuringExecution affinity. The scheduler attempts to schedule a pod to a node that matches the preferred rules. You can set node weights in preferred rules. Set the other parameters as described in the preceding settings.
        Note Weight: Set the weight of a preferred rule to a value from 1 to 100. The scheduler calculates the weight of each node that meets the preferred rule, and then schedules the pod to the node with the highest weight.
      Pod Anti Affinity
      Pod anti-affinity specifies that a pod is not scheduled to a node in the same topological domain if the node runs a pod that matches the anti-affinity rules. Pod anti-affinity rules apply to the following scenarios:
      • Schedule the pods of a Service to different topological domains, such as multiple hosts. This allows you to enhance the stability of the Service.
      • Grant a pod exclusive access to a node. This enables resource isolation and ensures that no other pod can share the resources of the specified node.
      • Schedule pods of Services to different hosts if these Services may interfere each other.
      Note You can set pod anti-affinity rules in the same way as setting pod affinity rules, and choose anti-affinity or pod affinity as needed.
      Toleration Set toleration rules to allow pods to be scheduled to nodes with matching taints.
      Schedule to Virtual Nodes Specify whether to schedule pods to virtual nodes. This option is unavailable if the cluster does not contain a virtual node.
    • Labels and Annotations
      • Pod Labels: Add a label to the pod. The label is used to identify the application.
      • Pod Annotations: Add an annotation to the pod.
  11. Click Create.
  12. After the application is created, you are redirected to the Complete page. You can find the resource objects under the application and click View Details to view application details.

    The details page of the created stateful application appears.

  13. In the upper-left corner of the page, click the Back icon to go to the StatefulSets page. On the StatefulSets page, you can view the created application.
  14. Optional:Click Scale in the Actions column to scale the application.
    1. In the Scale dialog box, set Desired Number of Pods to 3 and click OK. After you scale out the application, all pods in the application are listed in ascending order of ordinal indexes. If you scale in the application, pods are deleted in descending order of ordinal indexes. This ensures that all pods follow a specific order.
      Scale the application
    2. In the left-side navigation pane, choose Volumes > Persistent Volume Claims. You can find that after you scale out the application, new PVs and PVCs are created for the newly added pods. However, if the application is scaled in, existing PVs and PVCs are not deleted.

Related operations

In the left-side navigation pane, click Clusters. On the Clusters page, click the name of the cluster that you want to manage or click Applications in the Actions column. In the left-side navigation pane, click Workloads and StatefulSets. On the StatefulSets page, click the name of the application that you want to manage or click Details in the Actions column. On the details page of the application, you can edit, scale, redeploy, and refresh the application. You can also view the YAML file of the application.

  • Edit: On the details page of the application, click Edit in the upper-right corner of the page to modify the configurations of the application.
  • Scale: On the details page of the application, click Scale in the upper-right corner of the page to scale the application to a required number of pods.
  • View the YAML file: On the details page of the application, click View in YAML in the upper-right corner of the page. You can update and download the YAML file. You can also save the YAML file as a template.
  • Redeploy: On the details page of the application, click Redeploy in the upper-right corner of the page to redeploy the application.
  • Refresh: On the details page of the application, click Refresh in the upper-right corner of the page to refresh the application.

What to do next

Log on to a master node and perform the following commands to test the persistent storage.

  1. Run the following commands to create a temporary file in the cloud disk that is mounted to pod nginx-1:
    kubectl exec nginx-1 ls /tmp            #Query files in the /tmp directory.
    
    kubectl exec nginx-1 touch /tmp/statefulset         #Create a file named statefulset.
    
    kubectl exec nginx-1 ls /tmp
    lost+found
    statefulset
  2. Run the command to delete pod nginx-1 and verify data persistence:
    kubectl delete pod nginx-1
    pod"nginx-1" deleted
  3. After the system recreates and starts pod nginx-1, query the files in the /tmp directory. The following result shows that the statefulset file still exists. This indicates the high availability of the application that runs on the StatefulSet.
    kubectl exec nginx-1 ls /tmp                         #Query files in the /tmp directory.
    statefulset