The data is not being shared across containers - kubernetes

Question

I am trying to create two containers within a pod with one container being an init container. The job of the init container is to download a jar and make it available for the app container. I am able to create everything and the logs look good but when i check, i do not see the jar in my app container. Below is my deployment yaml:
apiVersion: apps/v1
kind: Deployment
metadata:
name: web-service-test
labels:
app: web-service-test
spec:
replicas: 1
selector:
matchLabels:
app: web-service-test
template:
metadata:
labels:
app: web-service-test
spec:
volumes:
- name: shared-data
emptyDir: {}
containers:
- name: web-service-test
image: some image
ports:
- containerPort: 8081
volumeMounts:
- name: shared-data
mountPath: /tmp/jar
initContainers:
- name: init-container
image: busybox
volumeMounts:
- name: shared-data
mountPath: /jdbc-jar
command:
- wget
- "https://repo1.maven.org/maven2/com/oracle/ojdbc/ojdbc8/19.3.0.0/ojdbc8-19.3.0.0.jar"

Answer 1

You need to save jar in the /jdbc-jar folder
try updating your yaml to following
command: ["/bin/sh"]
args: ["-c", "wget -O /pod-data/ojdbc8-19.3.0.0.jar https://repo1.maven.org/maven2/com/oracle/ojdbc/ojdbc8/19.3.0.0/ojdbc8-19.3.0.0.jar"]

Answer 2

Add following block of code to your init container section:
command: ["/bin/sh","-c"]
args: ["wget -O /jdbc-jar/ojdbc8-19.3.0.0.jar https://repo1.maven.org/maven2/com/oracle/ojdbc/ojdbc8/19.3.0.0/ojdbc8-19.3.0.0.jar"]
The command ["/bin/sh", "-c"] says "run a shell, and execute the following instructions". The args are then passed as commands to the shell. In shell scripting a semicolon separates commands. In the wget command I have added the -O flag to download the jar from the specified url and save it as /jdbc-jar/ojdbc8-19.3.0.0.jar .
To check if jar is persistent in container. Simply execute command:
$ kubectl exec -it web-service-test -- /bin/bash
Then go to folder /jdbc-jar ( $ cd jdbc-jar ) and list files in it ($ ls -al). You should see your jar there.
See examples: commands-in-containers, initcontainers-running.