CODEWITHSUNDEEP
kubernetescontainersopenshiftpersistent-volumesglusterfs
Arko
Arko

Reputation: 972

Is there an intermediate layer/cache between Kubernetes pod and Persistance volume, or does a pod access PV directly

Recently I ran into a strange problem. We have two pods running into an openshift cluster that shares a persistent volume (GlusterFs) between them. Now for the sake of this explanation, let's assume one of the pods was PodA and the Other was PodB, in this case, PodB was running for three months, there is automation in POdA which creates/updates files in the shared persistence volume and PodB reads it and perform some operation based on the input.

Now coming to the problem, whenever POdA created a new file in the shared PV it was visible and accessible from PodA. However, there were a few files that PodA was updating periodically, but the change was not reflected in PodB. So in PodB, we could only see the old version of those files. To solve that problem, we have forcefully deleted PodB, and then openshift recreated it, and the problem was gone.

I thought in PV mechanism Kubernetes mount external storage/folder into the pod (container), and there is no intermediate layer or cache or something like that. From what we have experienced so far, it seems every container (or pod) creates a local copy of those files, or maybe there is a cache in between (PV and pod),

I have searched about this on google and could not find a detailed explanation on how this PV mount works in Kubernetes , would love to know the actual reason behind this problem.

Upvotes: 0

Views: 1349

Answers (1)

Fritz Duchardt
Fritz Duchardt

Reputation: 11870

There is no caching mechanism for PVs provided by Kubernetes, so the problem you are observing must be located in either the GlusterFS CSI driver or GlusterFS itself.

Upvotes: 1

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