We have some Kubernetes cronjobs configured with a PVC (PersistentVolumeClaim), and during an upgrade of the cronjob, we needed to access the data it was using so we could clean some stuff. When your application is deployed using a Kubernetes Deployment resource is pretty straight forward, the pods are continuously running, and if you don’t use a scratch base image, you most of the time have access to some shell.
When you are using a standard deployment is very easy to access the mounted PVC by using
kubectl exec -ti somepod bash.
Unfortunately, we don’t have this possibility when we have CronJob resources since they tend to be more shortlived and start only at specific intervals. So I looked for an alternative solution 😛
The (Hacky) Solution
I came up with a straightforward deployment, which we could scale up once we need to examine the data — acting as a proxy to PVC.
The only problem I encounter was I need to have a command which would keep the
pods running. Luckily I learned that the sleep command
accepts infinity as duration parameter 😅
So once you apply the deployment, you can access a shell using
kubectl exec -ti explorer-... bash and examine or alter your data.
An example deployment
---
kind: Deployment
apiVersion: extensions/v1beta1
metadata:
name: explorer
spec:
replicas: 1
template:
metadata:
labels:
app: explorer
spec:
containers:
- name: explorer
image: debian
command: ["sleep", "infinity"]
volumeMounts:
- name: data
mountPath: /data
volumes:
- name: data
persistentVolumeClaim:
claimName: data
