Is this possible to schedule CronJob to execute on each of Kubernetes nodes?

Question

What I would like to do is to run some backup scripts on each of Kubernetes nodes periodically. I want it to run inside Kubernetes cluster in contrast to just adding script to each node's crontab. This is because I will store backup on the volume mounted to the node by Kubernetes. It differs from the configuration but it could be CIFS filesystem mounted by Flex plugin or awsElasticBlockStore.

It would be perfect if CronJob will be able to template DaemonSet (instead of fixing it as jobTemplate) and there will be possibility to set DaemonSet restart policy to OnFailure.

I would like to avoid defining n different CronJobs for each of n nodes and then associate them together by defining nodeSelectors since this will be not so convenient to maintain in environment where nodes count changes dynamically.

What I can see problem was discussed here without any clear conclusion: https://github.com/kubernetes/kubernetes/issues/36601

Maybe do you have any hacks or tricks to achieve this?

Answer 1

You can use DaemonSet with the following bash script:

  while :; do
   currenttime=$(date +%H:%M)
   if [[ "$currenttime" > "23:00" ]] && [[ "$currenttime" < "23:05" ]]; then
     do_something
   else
     sleep 60
   fi
   test "$?" -gt 0 && notify_failed_job
  done

Answer 2

Is this still the best way to mimic CronJob with a DaemonSet template. ie. run a crontab on all the nodes (based on a node selector)

I'm not against it but its a bummer I need to run these pods the whole time. It would be nice to have the k8s scheduler handle all this for me.