Deploying to Kubernetes' Local Persistent Storage via Helm

Question

Using Kubernetes 1.7.0, the intention here is to be able to deploy MySQL / MongoDB / etc, and use local disk as storage backing; while webheads, and processing pods can autoscale by Kubernetes. To these aims, I've

Set up & deployed the Local Persistent Storage provisioner to automatically provision locally attached disk to pods' Persitent Volume Claims.
Manually created a Persistent Volume Claim, which succeeds, and the local volume is attached
Attempted to deploy MariaDB via helm by

helm install --name mysql --set persistence.storageClass=default stable/mariadb
This appears to succeed; but by going to the dashboard, I get

Storage node affinity check failed for volume "local-pv-8ef6e2af" : NodeSelectorTerm [{Key:kubernetes.io/hostname Operator:In Values:[kubemaster]}] does not match node labels

I suspect this might be due to helm's charts not including nodeaffinity. Other than updating each chart manually, is there a way to tell helm to deploy to the same pod where the provisioner has the volume?

Maybe you could consider using NFS instead of attaching local volumes? — Maciek Sawicki

Ian Lewis Ian Lewis · Accepted Answer · 2017-07-10T01:36:04

Unfortunately, no. You will need to specify node affinity so that the Pod lands on the node where the local storage is located. See the docs on Node Affinity to know what do add to the helm chart.

I suspect it would look something like the following in your case.

affinity:
  nodeAffinity:
    requiredDuringSchedulingIgnoredDuringExecution:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - kubemaster

As an aside, this is something that will happen, not just at the node level, but at the zone level for cloud environments like AWS and GCP as well. In those environments, persistent disks are zonal and will require you to set NodeAffinity so that the Pods land in the zone with the persistent disk when deploying to a multi-zone cluster.

Also as an aside, It looks like your are deploying to the Kubernetes master? If so that may not be advisable since MySQL could potentially affect the master's operation.

Deploying to Kubernetes' Local Persistent Storage via Helm

1 Answers