Kubernetes copying jars into a pod and restart - kubernetes

Question

I have a Kubernetes problem where I need to copy 2 jars (each jar > 1Mb) into a pod after it is deployed. So ideally the solution is we cannot use configMap (> 1Mb) but we need to use "wget" in "initcontainer" and download the jars.
so below is my kubernetes-template configuration which i have modified. The original one is available at https://github.com/dremio/dremio-cloud-tools/blob/master/charts/dremio/templates/dremio-executor.yaml
{{ if not .Values.DremioAdmin }}
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: dremio-executor
spec:
serviceName: "dremio-cluster-pod"
replicas: {{.Values.executor.count}}
podManagementPolicy: "Parallel"
revisionHistoryLimit: 1
selector:
matchLabels:
app: dremio-executor
template:
metadata:
labels:
app: dremio-executor
role: dremio-cluster-pod
annotations:
dremio-configmap/checksum: {{ (.Files.Glob "config/*").AsConfig | sha256sum }}
spec:
terminationGracePeriodSeconds: 5
{{- if .Values.nodeSelector }}
nodeSelector:
{{- range $key, $value := .Values.nodeSelector }}
{{ $key }}: {{ $value }}
{{- end }}
{{- end }}
containers:
- name: dremio-executor
image: {{.Values.image}}:{{.Values.imageTag}}
imagePullPolicy: IfNotPresent
securityContext:
runAsUser: 0
resources:
requests:
memory: {{.Values.executor.memory}}M
cpu: {{.Values.executor.cpu}}
volumeMounts:
- name: dremio-executor-volume
mountPath: /opt/dremio/data
##################### START added this section #####################
- name: dremio-connector
mountPath: /opt/dremio/jars
#################### END added this section ##########################
- name: dremio-config
mountPath: /opt/dremio/conf
env:
- name: DREMIO_MAX_HEAP_MEMORY_SIZE_MB
value: "{{ template "HeapMemory" .Values.executor.memory }}"
- name: DREMIO_MAX_DIRECT_MEMORY_SIZE_MB
value: "{{ template "DirectMemory" .Values.executor.memory }}"
- name: DREMIO_JAVA_EXTRA_OPTS
value: >-
-Dzookeeper=zk-hs:2181
-Dservices.coordinator.enabled=false
{{- if .Values.extraStartParams }}
{{ .Values.extraStartParams }}
{{- end }}
command: ["/opt/dremio/bin/dremio"]
args:
- "start-fg"
ports:
- containerPort: 45678
name: server
initContainers:
################ START added this section ######################
- name: installjars
image: {{.Values.image}}:{{.Values.imageTag}}
imagePullPolicy: IfNotPresent
securityContext:
runAsUser: 0
volumeMounts:
- name: dremio-connector
mountPath: /opt/dremio/jars
command: ["/bin/sh","-c"]
args: ["wget --no-check-certificate -O /dir/connector.jar https://<some nexus repo URL>/connector.jar; sleep 10;"]
################ END added this section ###############
- name: wait-for-zk
image: busybox
command: ["sh", "-c", "until ping -c 1 -W 1 zk-hs > /dev/null; do echo waiting for zookeeper host; sleep 2; done;"]
# since we're mounting a separate volume, reset permission to
# dremio uid/gid
- name: chown-data-directory
image: {{.Values.image}}:{{.Values.imageTag}}
imagePullPolicy: IfNotPresent
securityContext:
runAsUser: 0
volumeMounts:
- name: dremio-executor-volume
mountPath: /opt/dremio/data
command: ["chown"]
args:
- "dremio:dremio"
- "/opt/dremio/data"
volumes:
- name: dremio-config
configMap:
name: dremio-config
{{- if .Values.imagePullSecrets }}
imagePullSecrets:
- name: {{ .Values.imagePullSecrets }}
{{- end}}
#################### START added this section ########################
- name: dremio-connector
emptyDir: {}
#################### END added this section ########################
volumeClaimTemplates:
- metadata:
name: dremio-executor-volume
spec:
accessModes: [ "ReadWriteOnce" ]
{{- if .Values.storageClass }}
storageClassName: {{ .Values.storageClass }}
{{- end }}
resources:
requests:
storage: {{.Values.executor.volumeSize}}
{{ end }}
So the above is NOT working and I don't see any jars being downloaded once I "exec" into the pod. I don't understand what is wrong with the above. however do note that inside the pod if i run the same wget command it does download the jar which baffles me. So the URL is working, readwrite of directory is no problem but still jar is not downloaded ???

Answer 1

If you can remove the need for Wget altogether it would make life easier...
Option 1
Using your own docker image will save some pain if thats an option
Dockerfile
# docker build -f Dockerfile -t ghcr.io/yourOrg/projectId/dockerImageName:0.0.1 .
# docker push ghcr.io/yourOrg/projectId/dockerImageName:0.0.1
FROM nginx:1.19.10-alpine
# Use local copies of config
COPY files/some1.jar /dir/
COPY files/some2.jar /dir/
Files will be ready in the container, no need for cryptic commands in your pod definition that will make little sense. Alternatively if you need to download the files you could copy a script to do that work into the Docker image instead and run that on startup via the docker directive CMD.
Option 2
Alternatively, you could do a two stage deployment...
Create a persistent volume
mount the volume to a pod (use busybox as a base?) that will run for enough time for the files to copy across from your local machine (or for them to be downloaded if you continue to use Wget)
kubectl cp the files you need to the (Retained) PersistentVolume
Now mount the PV to your pod's container(s) so the files are readily available when the pod fires up.

Answer 2

Your approch seems right.
Another solution could be to include the jar on the Docker image but I think it's not possible right ?
You could just use an emptyDir instead of a VolumeClaim.
Last one, I would have download the jar before waiting for ZooKeeper to gain some time.