How to use a Kubernetes cron job that applies a patch to a cluster node with information about the host network interface?

on

Q) How to use a Kubernetes cron job that applies a patch to a cluster node with information about the host network interface?                                                                                                Solution:    Both solutions are possible, but they have different implications and requirements. Here are some considerations that may help you choose the best approach for your use case :                                                                                                                                              

Option 1: Mount a volume for the container

This option requires creating a Kubernetes pod that runs the script and mounts a volume to share files between the host and the container. The volume can contain the script and the CSV file used to update the external IP of the services. Here are the main steps to implement this solution:                                                                                                                                                                                        

    1. Create a Kubernetes config map that contains the script and the CSV file:
sql
kubectl create configmap update-externalip --from-file=automatic_update_of_externalIP.sh --from-file=automatic_update_of_externalIP_services.csv
  1. Create a Kubernetes pod that runs the script and mounts the config map as a volume:
yaml
apiVersion: v1
kind: Pod
metadata:
  name: update-externalip
spec:
  containers:
  - name: update-externalip
    image: busybox:1.28
    command: ["/bin/sh", "-c"]
    args:
      - /mnt/automatic_update_of_externalIP.sh
    volumeMounts:
    - name: config
      mountPath: /mnt
  volumes:
  - name: config
    configMap:
      name: update-externalip
        1. Create a Kubernetes cron job that schedules the pod:
yaml
apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: job-automatic-update-externalip
spec:
  schedule: "*/10 * * * *"  # Run every 10 minutes
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: job-automatic-update-externalip
            image: busybox:1.28
            command:
            - /bin/sh
            - -c
            - "sleep 5 && kubectl apply -f /path/to/update-externalip-pod.yml"
            env:
            - name: KUBECONFIG
              value: /path/to/kube/config
            volumeMounts:
            - name: kubeconfig
              mountPath: /path/to/kube/config
          volumes:
          - name: kubeconfig
            hostPath:
              path: /root/.kube/config
              type: FileOrCreate

Some things to note about this solution:                

  • You need to provide the path to the kubeconfig file to allow the cron job container to access the Kubernetes API server and create the pod. You can mount a hostPath volume to the kubeconfig file, or use a ConfigMap to store the file contents.

  • You need to provide the sleep command before running kubectl apply to ensure that the Kubernetes API server is ready to accept requests. Otherwise, you may get errors like "Unable to connect to the server".

  • You need to set the restartPolicy to "OnFailure" in the pod template to allow the cron job to retry the pod if it fails.

Option 2: Create a normal cron job on the underlying VM        This option requires creating a cron job on the VM that runs the script directly, without involving Kubernetes. Here are the main steps to implement this solution:

  1. Create a cron job on the VM that runs the script: 
javascript
*/10 * * * * /home/VM_USER/automatic_update_of_externalIP.sh
  1. Make sure that the script has the right permissions to execute: 
bash
chmod +x /home/VM_USER/automatic_update_of_externalIP.sh

Some things to note about this solution:    You don't need to worry about Kubernetes permissions or network interfaces, since the script runs directly on the host.


Comments

Post a Comment