Requirements

Each node in the Kubernetes cluster where Longhorn is installed must fulfill the following requirements:

  • A container runtime compatible with Kubernetes (Docker v1.13+, containerd v1.3.7+, etc.)

  • Kubernetes ≥ v1.21

  • open-iscsi is installed, and the iscsid daemon is running on all the nodes. This is necessary, since Longhorn relies on iscsiadm on the host to provide persistent volumes to Kubernetes. For help installing open-iscsi, refer to this section.

  • RWX support requires that each node has a NFSv4 client installed.

  • The host filesystem supports the file extents feature to store the data. Currently we support:

    • ext4

    • XFS

  • bash, curl, findmnt, grep, awk, blkid, lsblk must be installed.

  • Mount propagation must be enabled.

The Longhorn workloads must be able to run as root in order for Longhorn to be deployed and operated properly.

This script can be used to check the Longhorn environment for potential issues.

For the minimum recommended hardware, refer to the best practices guide.

OS/Distro Specific Configuration

You must perform additional setups before using Longhorn with certain operating systems and distributions.

Using the Longhorn Command Line Tool

The longhornctl tool is a CLI for Longhorn operations. For more information, see Command Line Tool (longhornctl).

To check the prerequisites and configurations, download the tool and run the check sub-command:

# For AMD64 platform
curl -sSfL -o longhornctl https://github.com/longhorn/cli/releases/download/v1.7.0/longhornctl-linux-amd64
# For ARM platform
curl -sSfL -o longhornctl https://github.com/longhorn/cli/releases/download/v1.7.0/longhornctl-linux-arm64

chmod +x longhornctl
./longhornctl check preflight

Example of result:

INFO[2024-01-01T00:00:01Z] Initializing preflight checker
INFO[2024-01-01T00:00:01Z] Cleaning up preflight checker
INFO[2024-01-01T00:00:01Z] Running preflight checker
INFO[2024-01-01T00:00:02Z] Retrieved preflight checker result:
worker1:
  info:
  - Service iscsid is running
  - NFS4 is supported
  - Package nfs-common is installed
  - Package open-iscsi is installed
  warn:
  - multipathd.service is running. Please refer to https://longhorn.io/kb/troubleshooting-volume-with-multipath/ for more information.
worker2:
  info:
  - Service iscsid is running
  - NFS4 is supported
  - Package nfs-common is not installed
  - Package open-iscsi is installed

Use the install sub-command to install and set up the preflight dependencies before installing Longhorn.

./longhornctl install preflight

Note:
Some immutable Linux distributions, such as SUSE Linux Enterprise Micro (SLE Micro), require you to reboot worker nodes after running the install sub-command.

The documentation of the Linux distribution you are using should outline such requirements. For example, the SLE Micro documentation explains how all changes made by the transactional-update command become active only after the node is rebooted.

Using the Environment Check Script

Deprecation Notice
Since Longhorn v1.7.0, we have introduced the Longhorn Command Line Tool. The functionality of the environment check script, environment_check.sh overlaps with that of the Longhorn Command Line Tool. Therefore, the script has been deprecated in v1.7.0 and is scheduled for removal in v1.8.0.

We’ve written a script to help you gather enough information about the factors.

Note jq maybe required to be installed locally prior to running env check script.

To run script:

curl -sSfL https://raw.githubusercontent.com/longhorn/longhorn/v1.7.0/scripts/environment_check.sh | bash

Example of result:

[INFO]  Required dependencies 'kubectl jq mktemp sort printf' are installed.
[INFO]  All nodes have unique hostnames.
[INFO]  Waiting for longhorn-environment-check pods to become ready (0/3)...
[INFO]  All longhorn-environment-check pods are ready (3/3).
[INFO]  MountPropagation is enabled
[INFO]  Checking kernel release...
[INFO]  Checking iscsid...
[INFO]  Checking multipathd...
[INFO]  Checking packages...
[INFO]  Checking nfs client...
[INFO]  Cleaning up longhorn-environment-check pods...
[INFO]  Cleanup completed.

Pod Security Policy

Starting with v1.0.2, Longhorn is shipped with a default Pod Security Policy that will give Longhorn the necessary privileges to be able to run properly.

No special configuration is needed for Longhorn to work properly on clusters with Pod Security Policy enabled.

Notes on Mount Propagation

If your Kubernetes cluster was provisioned by Rancher v2.0.7+ or later, the MountPropagation feature is enabled by default.

If MountPropagation is disabled, Base Image feature will be disabled.

Root and Privileged Permission

Longhorn components require root access with privileged permissions to achieve volume operations and management, because Longhorn relies on system resources on the host across different namespaces, for example, Longhorn uses nsenter to understand block devices' usage or encrypt/decrypt volumes on the host.

Below are the directories Longhorn components requiring access with root and privileged permissions :

  • Longhorn Manager

    • /dev: Block devices created by Longhorn are under the /dev path.

    • /proc: Find the recognized host process like container runtime, then use nsenter to access the mounts on the host to understand disks usage.

    • /var/lib/longhorn: The default path for storing volume data on a host.

  • Longhorn Engine Image

    • /var/lib/longhorn/engine-binaries: The default path for storing the Longhorn engine binaries.

  • Longhorn Instance Manager

    • /: Access any data path on this node and access Longhorn engine binaries.

    • /dev: Block devices created by Longhorn are under the /dev path.

    • /proc: Find the recognized host process like container runtime, then use nsenter to manage iSCSI targets and initiators, also some file system

  • Longhorn Share Manager

    • /dev: Block devices created by Longhorn are under the /dev path.

    • /lib/modules: Kernel modules required by cryptsetup for volume encryption.

    • /proc: Find the recognized host process like container runtime, then use nsenter for volume encryption.

    • /sys: Support volume encryption by cryptsetup.

  • Longhorn CSI Plugin

    • /: For host checks via the NFS customer mounter (deprecated). Note that, this will be removed in the future release.

    • /dev: Block devices created by Longhorn are under the /dev path.

    • /lib/modules: Kernel modules required by Longhorn CSI plugin.

    • /sys: Support volume encryption by cryptsetup.

    • /var/lib/kubelet/plugins/kubernetes.io/csi: The path where the Longhorn CSI plugin creates the staging path (via NodeStageVolume) of a block device. The staging path will be bind-mounted to the target path /var/lib/kubelet/pods (via NodePublishVolume) for support single volume could be mounted to multiple Pods.

    • /var/lib/kubelet/plugins_registry: The path where the node-driver-registrar registers the CSI plugin with kubelet.

    • /var/lib/kubelet/plugins/driver.longhorn.io: The path where the socket for the communication between kubelet Longhorn CSI driver.

    • /var/lib/kubelet/pods: The path where the Longhorn CSI driver mounts volume from the target path (via NodePublishVolume).

  • Longhorn CSI Attacher/Provisioner/Resizer/Snapshotter

    • /var/lib/kubelet/plugins/driver.longhorn.io: The path where the socket for the communication between kubelet Longhorn CSI driver.

  • Longhorn Backing Image Manager

    • /var/lib/longhorn: The default path for storing data on the host.

  • Longhorn Backing Image Data Source

    • /var/lib/longhorn: The default path for storing data on the host.

  • Longhorn System Restore Rollout

    • /var/lib/longhorn/engine-binaries: The default path for storing the Longhorn engine binaries.

Installing open-iscsi

The command used to install open-iscsi differs depending on the Linux distribution.

For GKE, we recommend using Ubuntu as the guest OS image since it containsopen-iscsi already.

You may need to edit the cluster security group to allow SSH access.

  • SUSE and openSUSE: Run the following command:

    zypper install open-iscsi
systemctl enable iscsid
systemctl start iscsid

  • Debian and Ubuntu: Run the following command:

    apt-get install open-iscsi

  • RHEL, CentOS, and EKS (EKS Kubernetes Worker AMI with AmazonLinux2 image): Run the following commands:

    yum --setopt=tsflags=noscripts install iscsi-initiator-utils
echo "InitiatorName=$(/sbin/iscsi-iname)" > /etc/iscsi/initiatorname.iscsi
systemctl enable iscsid
systemctl start iscsid

  • Talos Linux: See Talos Linux Support.

  • Container-Optimized OS: See Container-Optimized OS Support

Please ensure iscsi_tcp module has been loaded before iscsid service starts. Generally, it should be automatically loaded along with the package installation.

modprobe iscsi_tcp
On SUSE and openSUSE, the iscsi_tcp module is included only in the kernel-default package. If the kernel-default-base package is installed on your system, you must replace it with kernel-default.

We also provide an iscsi installer to make it easier for users to install open-iscsi automatically:

kubectl apply -f https://raw.githubusercontent.com/longhorn/longhorn/v1.7.0/deploy/prerequisite/longhorn-iscsi-installation.yaml

After the deployment, run the following command to check pods' status of the installer:

kubectl -n longhorn-system get pod | grep longhorn-iscsi-installation
longhorn-iscsi-installation-49hd7   1/1     Running   0          21m
longhorn-iscsi-installation-pzb7r   1/1     Running   0          39m

And also can check the log with the following command to see the installation result:

kubectl -n longhorn-system logs longhorn-iscsi-installation-pzb7r -c iscsi-installation
...
Installed:
  iscsi-initiator-utils.x86_64 0:6.2.0.874-7.amzn2

Dependency Installed:
  iscsi-initiator-utils-iscsiuio.x86_64 0:6.2.0.874-7.amzn2

Complete!
Created symlink from /etc/systemd/system/multi-user.target.wants/iscsid.service to /usr/lib/systemd/system/iscsid.service.
iscsi install successfully

In rare cases, it may be required to modify the installed SELinux policy to get Longhorn working. If you are running an up-to-date version of a Fedora downstream distribution (e.g. Fedora, RHEL, Rocky, CentOS, etc.) and plan to leave SELinux enabled, see the KB for details.

Installing NFSv4 client

In Longhorn system, backup feature requires NFSv4, v4.1 or v4.2, and ReadWriteMany (RWX) volume feature requires NFSv4.1. Before installing NFSv4 client userspace daemon and utilities, make sure the client kernel support is enabled on each Longhorn node.

  • Check NFSv4.1 support is enabled in kernel

    cat /boot/config-`uname -r`| grep CONFIG_NFS_V4_1

  • Check NFSv4.2 support is enabled in kernel

    cat /boot/config-`uname -r`| grep CONFIG_NFS_V4_2

The command used to install a NFSv4 client differs depending on the Linux distribution.

We also provide an nfs installer to make it easier for users to install nfs-client automatically:

kubectl apply -f https://raw.githubusercontent.com/longhorn/longhorn/v1.7.0/deploy/prerequisite/longhorn-nfs-installation.yaml

After the deployment, run the following command to check pods' status of the installer:

kubectl -n longhorn-system get pod | grep longhorn-nfs-installation
NAME                                  READY   STATUS    RESTARTS   AGE
longhorn-nfs-installation-t2v9v   1/1     Running   0          143m
longhorn-nfs-installation-7nphm   1/1     Running   0          143m

And also can check the log with the following command to see the installation result:

kubectl -n longhorn-system logs longhorn-nfs-installation-t2v9v -c nfs-installation
...
nfs install successfully

Checking the Kubernetes Version

Use the following command to check your Kubernetes server version

kubectl version

Result:

Client Version: version.Info{Major:"1", Minor:"26", GitVersion:"v1.26.10", GitCommit:"b8609d4dd75c5d6fba4a5eaa63a5507cb39a6e99", GitTreeState:"clean", BuildDate:"2023-10-18T11:44:31Z", GoVersion:"go1.20.10", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"26", GitVersion:"v1.26.10+k3s2", GitCommit:"cb5cb5557f34e240e38c68a8c4ca2506c68b1d86", GitTreeState:"clean", BuildDate:"2023-11-08T03:21:46Z", GoVersion:"go1.20.10", Compiler:"gc", Platform:"linux/amd64"}

The Server Version should be ≥ v1.21.

Installing Cryptsetup and LUKS

Cryptsetup is an open-source utility used to conveniently set up dm-crypt based device-mapper targets and Longhorn uses LUKS2 (Linux Unified Key Setup) format that is the standard for Linux disk encryption to support volume encryption.

The command used to install the cryptsetup tool differs depending on the Linux distribution.

  • For Debian and Ubuntu, use this command:

    apt-get install cryptsetup

  • For RHEL, CentOS, Rocky Linux and EKS with EKS Kubernetes Worker AMI with AmazonLinux2 image, use this command:

    yum install cryptsetup

  • For SUSE/OpenSUSE, use this command:

    zypper install cryptsetup

Installing Device Mapper Userspace Tool

The device mapper is a framework provided by the Linux kernel for mapping physical block devices onto higher-level virtual block devices. It forms the foundation of the dm-crypt disk encryption and provides the linear dm device on the top of v2 volume. The device mapper is typically included by default in many Linux distributions. Some lightweight or highly customized distributions or a minimal installation of a distribution might exclude it to save space or reduce complexity

The command used to install the device mapper differs depending on the Linux distribution.

  • For Debian and Ubuntu, use this command:

    apt-get install dmsetup

  • For RHEL, CentOS, Rocky Linux and EKS with EKS Kubernetes Worker AMI with AmazonLinux2 image, use this command:

    yum install device-mapper

  • For SUSE/OpenSUSE, use this command:

    zypper install device-mapper