K8s hostPath volumes

charm
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1

Hi there,

I’m looking for a way to wire up a hostPath volume in a K8s charm, so that an existing directory on the K8s node is exposed to the charm. However, I haven’t found a way to do this.

AFAICT the Juju-native storage mechanism will either mount a new volume (via the kubernetes type storage) or use an emptyDir. Is that still correct? The K8s-native config I would like to approximate is:

# in a .spec for kind: Pod ...
  containers:
  - name: foo
    #
    # ... stuff ...
    #
    volumeMounts:
    - name: varlog
      mountPath: /var/log
    - name: varlibdockercontainers
      mountPath: /var/lib/docker/containers
      readOnly: true
  #
  # ... more stuff ...
  #
  volumes:
  - name: varlog
    hostPath:
      path: /var/log
  - name: varlibdockercontainers
    hostPath:
      path: /var/lib/docker/containers
2

This is in progress as I type this :smiley:

k8s charms currently support creating text files at specified mount points on the host volume.

   files:
      - name: configurations
        mountPath: /etc/mysql/conf.d
        files:
          custom_mysql.cnf: |
            [mysqld]
            skip-host-cache
            skip-name-resolve          
            query_cache_limit = 1M

We’ll extend this to support

  • hostpath volumes
  • configmap volumes
  • secret backed volumes
  • empty dir volumes

eg

   files:
      # text files (what we have now)
      - name: configurations
        mountPath: /etc/mysql/conf.d
        files:
          custom_mysql.cnf: |
            [mysqld]
            skip-host-cache
            skip-name-resolve          
            query_cache_limit = 1M

      # hostpath (files block is empty, else error)
      - name: myhostpathstuff
          mountPath: /host/etc/cni/net.d
          hostPath:
            path: /etc/cni/net.d

      # configmap
      - name: myconfigmapstuff
         mountPath: /etc/otherstuff
         configMap:
           name: foo  # this configmap here must be included in the `configmap` field.
         files:
           config.yaml: configkey
           foo.yaml: foo.key

      # emptyDir (files block is empty, else error)
      - name: myemptydirstuff
          mountPath: /etc/otherstuff
          emptyDir:
            medium: memory

For configMap and secret, files is optional. If unspecified, use all of the configMap keys.

1 Like
3

That is fantastic news, thanks @wallyworld. We’ll be happy to give this a go when it’s available.