Setting Container Lifecycle Parameters

Scenario

CCE provides callback functions for the lifecycle management of containerized applications. For example, if you want a container to perform a certain operation before stopping, you can register a hook function.

CCE provides the following lifecycle callback functions:

Start Command: executed to start a container. For details, see Setting Container Startup Commands.
Post-Start: executed immediately after a container is started. For details, see Post-Start Processing.
Pre-Stop: executed before a container is stopped. The pre-stop processing function helps you ensure that the services running on the pods can be completed in advance in the case of pod upgrade or deletion. For details, see Pre-Stop Processing.

Commands and Parameters Used to Run a Container

A Docker image has metadata that stores image information. If lifecycle commands and arguments are not set, CCE runs the default commands and arguments, that is, Docker instructions ENTRYPOINT and CMD, provided during image creation.

If the commands and arguments used to run a container are set during application creation, the default commands ENTRYPOINT and CMD are overwritten during image build. The rules are as follows:

**Table 1** Commands and parameters used to run a container
Image Entrypoint	Image CMD	Command to Run a Container	Parameters to Run a Container	Command Executed
[touch]	[/root/test]	Not set	Not set	[touch /root/test]
[touch]	[/root/test]	[mkdir]	Not set	[mkdir]
[touch]	[/root/test]	Not set	[/opt/test]	[touch /opt/test]
[touch]	[/root/test]	[mkdir]	[/opt/test]	[mkdir /opt/test]

Startup Commands

By default, the default command during image start. To run a specific command or rewrite the default image value, you must perform specific settings: For details, see Setting Container Startup Commands.

Post-Start Processing

Set the post-start processing parameters, as listed in Table 2.

**Table 2** Post-start processing parameters
Parameter	Description
CLI	Set commands to be executed in the container for post-start processing. The command format is Command Args[1] Args[2].... Command is a system command or a user-defined executable program. If no path is specified, an executable program in the default path will be selected. If multiple commands need to be executed, write the commands into a script for execution. Commands that are executed in the background or asynchronously are not supported. Example command: exec: command: - /install.sh - install_agent Enter /install install_agent in the script. This command indicates that install.sh will be executed after the container is created successfully.
HTTP request	Send an HTTP request for post-start processing. The related parameters are described as follows: Path: (optional) request URL. Port: (mandatory) request port. Host Address: (optional) IP address of the request. The default value is the IP address of the node where the container resides.

Pre-Stop Processing

When creating a workload and adding a container, expand Lifecycle.

Set pre-stop parameters, as shown in Table 2.

**Table 3** Pre-stop parameters
Parameter	Description
CLI	Set commands to be executed in the container for pre-stop processing. The command format is Command Args[1] Args[2].... Command is a system command or a user-defined executable program. If no path is specified, an executable program in the default path will be selected. If multiple commands need to be executed, write the commands into a script for execution. Example command: exec: command: - /uninstall.sh - uninstall_agent Enter /uninstall uninstall_agent in the script. This command indicates that the uninstall.sh script will be executed before the container completes its execution and stops running.
HTTP request	Send an HTTP request for pre-stop processing. The related parameters are described as follows: Path: (optional) request URL. Port: (mandatory) request port. Host Address: (optional) IP address of the request. The default value is the IP address of the node where the container resides.

Container Restart Policy

The restartPolicy field is used to specify the pod restart policy. The restart policy type can be Always, OnFailure, or Never. The default value is Always.

When restartPolicy is used, containers are restarted only through kubelet on the same node.

Restart Policy	Description
Always	When a container fails, kubelet automatically restarts the container.
OnFailure	When the container stops running and the exit code is not 0, kubelet automatically restarts the container.
Never	kubelet does not restart the container regardless of the container running status.

Controllers that can manage pods include ReplicaSet Controllers, jobs, DaemonSets, and kubelet (static pod).

ReplicaSet Controller and DaemonSet: The policy must be set to Always to ensure that containers run continuously.
Job: The policy can be set to OnFailure or Never to ensure that containers are not restarted after being executed.
kubelet will restart a pod whenever it fails, regardless of the value of restartPolicy. In addition, no health check is performed on the pod.

Example YAML for Setting the Container Lifecycle

This section uses Nginx as an example to describe how to set the container lifecycle.

Use kubectl to connect to the cluster. For details, see Connecting to a Cluster Using kubectl.

Create and edit the nginx-deployment.yaml file. nginx-deployment.yaml is an example file name, and you can change it as required.

vi nginx-deployment.yaml

In the following configuration file, the postStart command is defined to run the install.sh command in the /bin/bash directory. preStop is defined to run the uninstall.sh command.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  strategy:
    type: RollingUpdate
  template:
    metadata:
      labels:
        app: nginx
    spec:
      restartPolicy: Always               #Restart policy
      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