Allow kadalu volumes to be mounted externally (outside k8s)

[amarts]

few users started asking for such features.

A storage volume started with kadalu operator. Now, from an external node which has access to reach gluster server pods wants to mount the volume.

There can be 2 type of users, 1 - use complete volume, or 2nd type is those who wants to use only 1 PV out of the storage on external node.

[amarts]

Possible Solution:

Phase1 - Static

1. Build a very simple REST API server app which serves gluster volfile as response when a particular GET call is made.
2. In this server - keep a watch on configMap, and like how we do generate_client_volfile in csi/volumeutils.py today, generate client file, and respond.
3. Provide a mount binary/script which does a HTTP GET call internally, and fetches the volfile.

Phase2 - Dynamic

• Implement a websocket and update the client volfile, and send SIGHUP signal to mount when client volfile changes.

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• This REST API server can be residing in kadalu operator pod itself as a container, so it is easier to watch for config change.
• Ideally, great if moana project also implements a feature like this so the mount scripts can be same for both.

[leelavg]

Looks cool, is it possible to answer 'why' such a feature is required? Is it some kubevirt use case?

[aravindavk]

It is kind of generic use case.

• Apps running outside the K8s and only Storage is provisioned from K8s
• Storage k8s Cluster is different than the apps K8s Cluster

[leelavg]

Makes sense, thanks for the explanation.

[aravindavk]

Looks good. One thing to explore is that the availability of Server pods from outside. Let us say If the generated Volfile contains server hostname as server1.kube1 and how to make that accessible as is from the external node?

• Option 1: Update Client machines /etc/hosts to respective IP mappings(Difficult if the public IP of these server pods may be changing)
• Option 2: Expose these server hostnames to client machine outside the K8s cluster.

Similar thing is required for Operator pod as well. Need a way to access the ReST APIs from Operator Pod.

[aravindavk]

Another issue is related to Authentication. ReST API can implement auth roles so that only authorized will get the Volfile. But how to handle if server pods are directly accessible.

• If Full Volume mount is required - TLS/SSL based client-brick communication is the possibility
• Subvolume/PV access - Not sure how to prevent a Client from accessing another Volume other than the one exposed.