mount options for host volumes

[kpweiler]

Nomad version

1.8.4

Operating system and Environment details

Ubuntu 22.04.5

Issue

I'm trying to mount an autofs mount from the host system into an exec driver task and getting Too many levels of symbolic links error when accessing the mount.

My assumption is that, with the exec driver, nomad is creating a bind mount mount --bind ... in the chroot'd directory from the host. This, in fact, will work if instead nomad were to use mount --rbind ... as rbind will follow submounts. The way I read the documentation, the host-to-task parameter should probably do this on host volumes. You could, alternatively, allow host volumes to set mount options.

Job file (if appropriate)

From the client config:

  host_volume "testvolume" {
    path      = "/testvolume"
    read_only = false
  }

And the full job spec:

job "example-job" {
  datacenters = ["ny5"]
  node_pool   = "bare_metal"

  type        = "batch"

  group "example-job" {

    volume "testvolume" {
      type = "host"
      source = "testvolume"
      read_only = false
    }

    task "example-job" {

      resources {
        memory = 128
      }

      volume_mount {
        volume      = "testvolume"
        destination = "/testvolume"
        read_only   = false
        propagation_mode = "bidirectional"
      }

      driver = "exec"
      config {
        command  = "ls"
        args     = ["/testvolume/testdata/test.txt"]
      }
    }
  }
}

[tgross]

Hi @kpweiler! This is a timely issue, for sure, as we're currently working on host volume improvements as part of #15489. The MountConfig we end up with is actually the libcontainer runc.Mount structure which allows mount flags.

The volume request (the object in the volume block in the jobspec) already supports mount_options.mount_flags, so it'd be a matter of mapping that to the flags in the runc object. I'll look into getting this added as part of the Dynamic Host Volumes work.