Configuring the Container Lifecycle

Startup Command

A startup command is executed when a container starts. It is used to define the main process of a container. The main process status determines the container lifecycle. If the command fails to be executed and no restart policy is configured, the container will be terminated.

By default, the default command is executed during image start. To run a specific command or rewrite the default image setting, you must perform specific operations. By default, the container executes the startup command preset in the image. Docker images contain a set of metadata fields for defining the startup behavior, including ENTRYPOINT and CMD. If the commands and arguments (specified by Command and Args) are not configured in the container specifications, the default values during image build are used.

If the commands and arguments used to run a container are set during workload creation, the default commands ENTRYPOINT and CMD are overwritten during image build.

1. Log in to the CCE console.
2. Click the cluster name to go to the cluster console, choose Workloads in the navigation pane, and click Create Workload in the upper right corner.
3. In Container Settings, choose Container Information > Lifecycle > Startup Command and enter the command and arguments.
   Figure 1 Configuring a startup command
   

   Table 2 Container startup command

   Parameter	Example Value	Description	Example YAML
   Command	/run/server	Enter one or more executable commands. If you need multiple commands, separate them on different lines. NOTE: In the case of multiple commands, you are advised to run /bin/sh or other shell commands. Other commands are used as parameters.	... spec: containers: - image: nginx:latest command: - /run/server args: - '--port=8080' ...
   Args	--port=8080	Enter one or more arguments. If you need multiple arguments, separate them on different lines.

4. Configure other parameters and click Create Workload in the lower right corner. If the workload is in the Running state, the startup command is successfully executed.

PostStart Hook

A PostStart hook, a container lifecycle hook provided by Kubernetes, is used to execute initialization tasks, such as service registration and dynamic configuration generation, immediately after the main process of a container starts. This hook is asynchronously triggered by kubelet and runs in parallel with the main process. Although the PostStart hook is executed asynchronously with the main process of the container, if the PostStart hook takes too long or is suspended, the container may not change to the Running state. If the PostStart hook fails to be executed, the container may fail to start and be terminated.

1. Log in to the CCE console.
2. Click the cluster name to go to the cluster console, choose Workloads in the navigation pane, and click Create Workload in the upper right corner.
3. In Container Settings, choose Container Information > Lifecycle > Post-Start and configure the parameters based on service requirements.
   • If initialization logic (such as running scripts and configuring the environment) needs to be executed in the container, select CLI.
   • If external systems or services needs to be notified (for example, when service registration is needed and a configuration center API is called), select HTTP request.
   Figure 2 CLI
   

   Table 3 Post-start processing

   Processing Method	Example Value	Description	Example YAML
   CLI	/install.sh install_agent	Used for running the commands in the container. You need to configure Command. The command format is Command Arg[1] Arg[2]..., where Command indicates a system command or a user-defined executable program. If no path is specified, the system searches for the command in the default path. If multiple commands needed to be executed, write them into a script in the container image in advance and invoke the script using this command. The executable command must be executed synchronously or in the frontend. If it is executed asynchronously or in the backend, the lifecycle hook may fail to be executed.	... lifecycle: postStart: exec: command: - /install.sh - install_agent ...
   HTTP request	Path: /nginx Port: 80 Host: 127.0.0.1	Used for initiating an HTTP request. The related parameters are described as follows: Path: (optional) request URL. Port: (mandatory) requested port. Host: (optional) requested host IP address. The default value is the IP address of the pod.	lifecycle: postStart: httpGet: path: /nginx port: 80 host: 127.0.0.1 scheme: HTTP ...

4. Configure other parameters and click Create Workload in the lower right corner. If the workload is in the Running state, the startup command is successfully executed.

PreStop Hook

If a container crashes or exits abnormally, the PreStop hook will not be triggered. The pod's termination grace period starts to count down before the PreStop hook is executed. Regardless of the outcome of the hook handler, the container will be terminated within the pod's termination grace period unless the finalizer delays the termination process. Other management operations on the container are blocked until the PreStop hook is complete or the termination grace period is reached.

1. Log in to the CCE console.
2. Click the cluster name to go to the cluster console, choose Workloads in the navigation pane, and click Create Workload in the upper right corner.
3. In Container Settings, choose Container Information > Lifecycle > Pre-Stop and configure the parameters based on service requirements.
   Figure 3 PreStop
   

   Table 4 Pre-stop processing parameters

   Parameter	Example Value	Description	Example YAML
   CLI	/uninstall.sh uninstall_agent	Used for running the commands in the container. You need to configure Command. The command format is Command Arg[1] Arg[2]..., where Command indicates a system command or a user-defined executable program. If no path is specified, the system searches for the command in the default path. If multiple commands needed to be executed, write them into a script in the container image in advance and invoke the script using this command.	... lifecycle: preStop: exec: command: - /uninstall.sh - uninstall_agent ...
   HTTP request	Path: /nginx Port: 80 Host: 127.0.0.1	Used for initiating an HTTP request. The related parameters are described as follows: Path: (optional) request URL. Port: (mandatory) requested port. Host: (optional) requested host IP address. The default value is the IP address of the pod.	lifecycle: preStop: httpGet: path: /nginx port: 80 host: 127.0.0.1 scheme: HTTP ...

4. Configure other parameters and click Create Workload in the lower right corner. If the workload is in the Running state, the startup command is successfully executed.

YAML Example

Nginx is used as an example to describe how to set the container lifecycle.

In the following configuration file, there is a PostStart command (install.sh) in the /bin/bash directory and a PreStop command (uninstall.sh).

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - image: nginx 
        command:
        - sleep 3600                        #Startup command
        imagePullPolicy: Always
        lifecycle:
          postStart:
            exec:
              command:
              - /bin/bash
              - install.sh                  #Post-Start command
          preStop:
            exec:
              command:
              - /bin/bash
              - uninstall.sh                 #Pre-Stop command
        name: nginx
      imagePullSecrets:
      - name: default-secret