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Prepare the worker node

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All of the worker nodes in the Kubernetes cluster need to be able to mount the volumes that you have provisioned for your pods. If you are using the ontap-nas, ontap-nas-economy, or ontap-nas-flexgroup driver for one of your backends, your worker nodes need the NFS tools. Otherwise they require the iSCSI tools.

Recent versions of RedHat CoreOS have both NFS and iSCSI installed by default.

Warning You should always reboot your worker nodes after installing the NFS or iSCSI tools, or else attaching volumes to containers might fail.

NFS volumes

Protocol Operating system Commands

NFS

RHEL/CentOS

sudo yum install -y nfs-utils

NFS

Ubuntu/Debian

sudo apt-get install -y nfs-common
Note You should ensure that the NFS service is started up during boot time.

iSCSI volumes

Consider the following when using iSCSI volumes:

  • Each node in the Kubernetes cluster must have a unique IQN. This is a necessary prerequisite.

  • If using RHCOS version 4.5 or later, or RHEL or CentOS version 8.2 or later with the solidfire-san driver, ensure that the CHAP authentication algorithm is set to MD5 in /etc/iscsi/iscsid.conf.

sudo sed -i 's/^\(node.session.auth.chap_algs\).*/\1 = MD5/' /etc/iscsi/iscsid.conf

  • When using worker nodes that run RHEL/RedHat CoreOS with iSCSI PVs, make sure to specify the discard mountOption in the StorageClass to perform inline space reclamation. See RedHat’s documentation.

Protocol Operating system Commands

iSCSI

RHEL/CentOS

  1. Install the following system packages:

    sudo yum install -y lsscsi iscsi-initiator-utils sg3_utils device-mapper-multipath

  2. Check that iscsi-initiator-utils version is 6.2.0.874-2.el7 or later:

    rpm -q iscsi-initiator-utils

  3. Set scanning to manual:

    sudo sed -i 's/^\(node.session.scan\).*/\1 = manual/' /etc/iscsi/iscsid.conf

  4. Enable multipathing:

    sudo mpathconf --enable --with_multipathd y

  5. Ensure that iscsid and multipathd are running:

    sudo systemctl enable --now iscsid multipathd

  6. Enable and start iscsi:

    sudo systemctl enable --now iscsi

iSCSI

Ubuntu/Debian

  1. Install the following system packages:

    sudo apt-get install -y open-iscsi lsscsi sg3-utils multipath-tools scsitools

  2. Check that open-iscsi version is 2.0.874-5ubuntu2.10 or later (for bionic) or 2.0.874-7.1ubuntu6.1 or later (for focal):

    dpkg -l open-iscsi

  3. Set scanning to manual:

    sudo sed -i 's/^\(node.session.scan\).*/\1 = manual/' /etc/iscsi/iscsid.conf

  4. Enable multipathing:

    sudo tee /etc/multipath.conf <←'EOF'
    defaults {
    user_friendly_names yes
    find_multipaths yes
    }
    EOF
    sudo systemctl enable --now multipath-tools.service
    sudo service multipath-tools restart

  5. Ensure that open-iscsi and multipath-tools are enabled and running:

    sudo systemctl status multipath-tools
    sudo systemctl enable --now open-iscsi.service
    sudo systemctl status open-iscsi
Note For Ubuntu 18.04, you must discover target ports with iscsiadm before starting open-iscsi for the iSCSI daemon to start. You can alternatively modify the iscsi service to start iscsid automatically.
Note If you want to learn more about automatic worker node preparation, which is a beta feature, see here.