Code for Run Once DaemonSet on Kubernetes http://blog.phymata.com/2017/05/13/run-once-daemonset-on-kubernetes/

cat-etc-hosts.sh

#!/bin/sh

set -euo pipefail

# gracefully handle the TERM signal sent when deleting the daemonset
trap 'exit' TERM

# do the work
# the /etc/hosts file of the node is mapped to /node/etc/hosts
cat /node/etc/hosts

# let the monitoring script know we're done'
echo "done"

# this is a workaround to prevent the container from exiting 
# and k8s restarting the daemonset pod
while true; do sleep 1; done

daemonset.yaml

apiVersion: extensions/v1beta1
kind: DaemonSet
metadata:
  name: cat-etc-hosts
spec:
  template:
    metadata:
      labels:
        run-once-daemonset: cat-etc-hosts
    spec:
      containers:
      - name: cat-etc-hosts
        image: etoews/cat-etc-hosts
        imagePullPolicy: Always
        volumeMounts:
        - name: etc-hosts
          mountPath: /node/etc/hosts
          readOnly: true
      volumes:
      - name: etc-hosts
        hostPath:
          path: /etc/hosts

Dockerfile

FROM alpine:3.5

COPY cat-etc-hosts.sh .

RUN chmod u+x cat-etc-hosts.sh

CMD ["./cat-etc-hosts.sh"]

run-once-daemonset.sh

#!/bin/bash

set -euo pipefail

function main() {
  kubectl apply -f daemonset.yaml
  wait_for_pods cat-etc-hosts
  wait_for_cats cat-etc-hosts
  kubectl delete -f daemonset.yaml
}

function wait_for_pods() {
  echo -n "waiting for $1 pods to run"

  PODS=$(kubectl get pods | grep $1 | awk '{print $1}')

  for POD in ${PODS}; do
    while [[ $(kubectl get pod ${POD} -o go-template --template "{{.status.phase}}") != "Running" ]]; do
      sleep 1
      echo -n "."
    done
  done

  echo
}

function wait_for_cats() {
  echo -n "waiting for $1 daemonset to complete"

  PODS=$(kubectl get pods | grep $1 | awk '{print $1}')

  for POD in ${PODS}; do
    while [[ $(kubectl logs ${POD} --tail 1) != "done" ]]; do
      sleep 1
      echo -n "."
    done
    
    # at this point you could take the output of kubectl logs and do something with it
  done

  echo
}

main

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