kubernetes sidecar pattern

sidecar-app-demo.yaml

apiVersion: v1
kind: Pod
metadata:
  labels:
    run: sidecar-app
  name: sidecar-app
  namespace: myns
spec:
  volumes:
    - name: data-volume
      emptyDir: {}

  containers:
    - image: ubuntu
      name: sidecar
      command: [
          'sh',
          '-c',
          'echo start:$(date) > /var/ftp/start.txt;
          apt update && apt upgrade -y && apt install lftp -y &&
          echo Finish:$(date) > /var/ftp/done.txt && sleep 100;
          while true; do lftp ftp-svc.myns.svc.cluster.local -e " mput /var/ftp/data/data*.txt && exit";
          echo Processed file ...;
          sleep 5; done',
        ]
      volumeMounts:
        - mountPath: /var/ftp
          name: data-volume
      startupProbe:
        exec:
          command:
            - cat
            - /var/ftp/done.txt
        periodSeconds: 12
        failureThreshold: 7
      resources: {}
    - image: busybox
      name: main-app
      command: ['/bin/sh']
      args: [
          '-c',
          'mkdir /ftp/data;while true; do  dt=$(shuf -i 0-100000 -n 1);
          echo $(date):= Hello > /ftp/data/data-${dt}.txt ;
          sleep 5;done',
        ]
      readinessProbe:
        exec:
          command:
            - cat
            - /ftp/done.txt
        periodSeconds: 12
        failureThreshold: 10
      volumeMounts:
        - mountPath: /ftp
          name: data-volume
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}