<p>After migrating the image type from container-vm to cos for the nodes of a GKE cluster, it seems no longer possible to mount a NFS volume for a pod.</p>

<p>The problem seems to be missing NFS client libraries, as a mount command from command line fails on all COS versions I tried (cos-stable-58-9334-62-0, cos-beta-59-9460-20-0, cos-dev-60-9540-0-0).</p>

<pre><code>sudo mount -t nfs mynfsserver:/myshare /mnt
</code></pre>

<p>fails with</p>

<pre><code>mount: wrong fs type, bad option, bad superblock on mynfsserver:/myshare,
       missing codepage or helper program, or other error
       (for several filesystems (e.g. nfs, cifs) you might
       need a /sbin/mount.&lt;type&gt; helper program)
</code></pre>

<p>But this contradicts the supported volume types listed here:
<a href="https://cloud.google.com/container-engine/docs/node-image-migration#storage_driver_support" rel="nofollow noreferrer">https://cloud.google.com/container-engine/docs/node-image-migration#storage_driver_support</a></p>

<p>Mounting a NFS volume in a pod works in a pool with image-type <code>container-vm</code> but not with <code>cos</code>.</p>

<p>With cos I get following messages with <code>kubectl describe pod</code>:</p>

<pre><code>MountVolume.SetUp failed for volume "kubernetes.io/nfs/b6e6cf44-41e7-11e7-8b00-42010a840079-nfs-mandant1" (spec.Name: "nfs-mandant1") pod "b6e6cf44-41e7-11e7-8b00-42010a840079" (UID: "b6e6cf44-41e7-11e7-8b00-42010a840079") with: mount failed: exit status 1
Mounting command: /home/kubernetes/containerized_mounter/mounter
Mounting arguments: singlefs-1-vm:/data/mandant1 /var/lib/kubelet/pods/b6e6cf44-41e7-11e7-8b00-42010a840079/volumes/kubernetes.io~nfs/nfs-mandant1 nfs []
Output: Mount failed: Mount failed: exit status 32
Mounting command: chroot
Mounting arguments: [/home/kubernetes/containerized_mounter/rootfs mount -t nfs singlefs-1-vm:/data/mandant1 /var/lib/kubelet/pods/b6e6cf44-41e7-11e7-8b00-42010a840079/volumes/kubernetes.io~nfs/nfs-mandant1]
Output: mount.nfs: Failed to resolve server singlefs-1-vm: Temporary failure in name resolution
</code></pre>

<p>Martin, are you setting up the mounts manually (executing mount yourself), or are you letting kubernetes do it on your behalf via a pod referencing an NFS volume?</p>

<p>The former will not work. The later will. As you've discovered COS does not ship with NFS client libraries, so GKE gets around this by setting up a chroot (at /home/kubernetes/containerized_mounter/rootfs) with the required binaries and calling mount inside that.</p>
