What is the best way to exec into another container and access its directory? - kubernetes

Question

I have a container running inside a pod and I want to be able to monitor its content every week. I want to write a Kube cronjob for it. Is there a best way to do this?
At the moment I am doing this by running a script in my local machine that does kubectl exec my-container and monitors the content of the directory in that container.

Answer 1

kubectl exec my-container sounds perfectly fine to me. You might want to look at this if you want to run kubectl in a pod (Kubernetes CronJob).
There are other ways but depending on what you are trying to do in the long term it might be an overkill. For example:
You can set up a Fluentd or tail/grep sidecar (or ls, if you are using a binary file?) to send the content or part of the content of that file to an Elasticsearch cluster.
You can set up Prometheus in Kubernetes to scrape metrics on the pod mounted filesystems. You will probably have to use a custom exporter in the pod or something else that exports files in mount points in the pod. This is a similar example.

Answer 2

You can run your script in another sidecar of your pod.
Define a empty directory volume
Mount this volume as your content directory
Also mount this directory to sidecar, so that it can access and able to monitor.
Example:
apiVersion: v1
kind: Pod
metadata:
name: monitor-by-sidecar
spec:
restartPolicy: Never
volumes: # empty directory volume
- name: shared-data
emptyDir: {}
containers:
- name: container-which-produce-content # This container is main application which generate contect. Suppose in /usr/share/nginx/html directory
image: debian
volumeMounts:
- name: shared-data
mountPath: /usr/share/nginx/html
command: ["/bin/bash", "-c"]
args:
- while true;
do
echo "hello world";
echo "----------------" > /usr/share/nginx/html/index.html;
cat /usr/share/nginx/html/index.html;
done
- name: container-which-run-script-to-monitor # this container will run your monitor scripts. this container mount main application's volume in /pod-data directory and run required scripts.
image: debian
volumeMounts:
- name: shared-data
mountPath: /pod-data
command: ["/bin/sh", "-c"]
args:
- while true;
do
echo "hello";
sleep 10;
ls -la /pod-data/;
cat /pod-data/index.html;
done
Example Description
First container(named container-which-produce-content) is main application, which mount a emptyDir volume in /usr/share/nginx/html. In this directory main application will generate data.
Second container(named container-which-run-script-to-monitor) will mount same emptyDir volume (named shared-data which also mounted by main application in /usr/share/nginx/html dir) in /pod-data directory. This /pod-data contains whole data which main application generated in /usr/share/nginx/html directory. You can then run your scripts on this directory.