This is a basic quickstart guide for the CentOS 7 version of the XSEDE Compatible Basic Cluster, based on the OpenHPC Project. ( It covers initial setup of your hardware (or virtual machines), configuration options for the ansible scripts, and a brief walkthrough of how to use the scripts.

The provided scripts are designed to be able to provision three types of nodes: basic compute nodes, login nodes, and GPU nodes.

By the end of the guide, you should have a working cluster with running Slurmctld, which can accept and run jobs on all nodes.

If you encounter errors, have questions, suggestions, or comments, please contact the XCRI Team by emailing Be sure to ask for the XCRI team!

XCBC Overview

The XCBC project is designed to provide the basic software necessary to create and HPC environment similar to that found on XSEDE resources, with open-source software and a minimum of fuss.

We use the OpenHPC repositories (link) for setup of the cluster management software and scheduler.

Ansible is used in this toolkit to provide an idempotent, non-invasive method of managing the cluster headnode. Ideally, the admin installing the cluster will only have to customize a single file before running the included playbooks. This guide walks the user through the cluster build by actually running the ansible playbooks locally on the headnode, but this could be done from a different machine just as easily, with a few tweaks to the inventory file. We did not wish to force the reader to make changes to some local machine, and so elected to keep everything on the VMs built specifically for this guide.

All of the (intended) customizable variables exist in the '''group_vars/all''' file, which is described in more detail below (Section 3: Defining Cluster Parameters)

The installation process, at a high level, takes place in six phases: (ignoring hardware/VM setup) 1. Installation of the bare OS on the headnode 2. Installation of the XCBC toolkit scripts and dependencies 3. Defining cluster parameters 4. Configuration of the headnode via Ansible 5. Installation of the compute nodes 6. Testing the scheduler

This guide in particular will walk through the steps of building an XCBC using VMs defined in VirtualBox, though this generalizes very well to a bare-metal deployment as well.

Common Acronyms and Abbreviations

XCBC = XSEDE Compatible Basic Cluster

XNIT = XSEDE National Integration Toolkit

WW = Warewulf - the cluster management software preferred in the OpenHPC project.

VM = Virtual Machine

NIC = Network Interface Card

NAT = Network Address Translation - used by Virtualbox to provide a connection from the Headnode VM to the outside world.

OS = Operating System

HPC = High Performance Computing/Cluster/Computer

Initial Setup On Hardware

For this guide, we're assuming you have access to three physical machines: One for the headnode, and two computes. The headnode should have at least 30GB of disk space, and 4GB of RAM, and each compute should have at least 4GB of RAM - local disk is optional. We're not setting up a secondary storage network here, so a single NIC per node is sufficient, but having two on the headnode would allow you to work remotely through ssh.

For the internal network, a "dumb" ethernet switch is all that's needed. Before beginning the OS installation on the headnode, install ethernet cables between the all nodes and your switch. The rest of the network configuration will take place during the OS installation.

Initial Setup On VirtualBox

Create (at least) two VM’s - one to be the headnode, and one to be a compute node.

For the headnode, activate three network interfaces, attached to NAT, Internal Network, and Host-only. (For hardware you would require only two, but having both NAT and host-only simplifies configuration on the headnode.)

In this configuration, the assumption is that there is a host-only network on Virtualbox configured with the internal DHCP server on. (Under File->Preferences->Networking->Host-only Networks). The default network is, but feel free to change this as you prefer.

1. Configure the network interfaces on the headnode. There are three: one for NAT, which provides connection to the outside world, one for a host-only network, and one for the internal network, which connects to compute nodes.

The host-only network is for an ssh connection into the main host. You could also use this as the interface for the headnode in an ansible inventory file, and run these roles against the headnode remotely. Use the DHCP server provided by Virtualbox; you will find the ip address given to the VM after installation of the OS. It is possible to use a static IP, but this is somewhat unreliable on successive reboots or image copies.

For the compute nodes, define two virtual machines, 'compute-0' and 'compute-1' with the boot order (Under 'Settings->General') set to Network ONLY, and a single ethernet interface, on the internal network. DO NOT INSTALL ANYTHING ON THESE VMs - The images will be generated and pushed out from the headnode during this tutorial. Make sure they have at least 2GB of RAM - otherwise the disk images built in this tutorial will be too large, and you will encounter mysterious errors.

Building the Cluster

Installation of the base OS on the headnode

1. Install CentOS 7.x minimal, on the headnode VM,

During installation, the default partition setup is fine. It helps to set up the three network interfaces at this point. Don't touch the 'NAT' interface, other than to check the 'Always Connect' box under 'Configure->General'. The same goes for the 'host-only' network.

Configure the internal network interface to have address, netmask /24 and gateway - the headnode will act as router for the compute nodes.

/24 is important, so that Warewulf will see the compute nodes as existing on the same network as the headnode interface!!! Don't forget to also check the 'Always Connect' box.

2. After installation, check the ip of your headnode on the host-only adapter via

  ip addr

Compare the MAC addresses of the interfaces on your headnode with those listed in Virtualbox, to be sure you substitute the correct device names below! (Typically, they show up as something like enp0s3,enp0s8, etc. - it pays to double-check!)

The NAT ip address will be used sparingly in the following documentation, but will be called $public-nic. Virtualbox assigns these as 10.0.x.15, where x begins at 2 for the 1st VM, 3 for the 2nd, etc.

Save the ip address of the interface on the host-only network - you'll use this as the address for the headnode in the ansible scripts, and it will be referred to as $host-nic

The ip address for the internal nic was set earlier, and will be referred to either as or $internal-nic

Make sure that the host-only and internal adapters are not set as default routes - ip route show should not list them as default! If you do see this, something like ip route del default via should do the trick, along with editing 'DEFROUTE=no' in the relevant /etc/sysconfig/network-scripts/ifcfg- file.

After checking the interfaces, ensure that the private nic is set in the internal firewall zone, and that the public is set in the public firewall zone.

  nmcli connection modify $internal-nic internal
  nmcli connection modify $public-nic public

You may also need to ensure that the connections will autoconnect on reboot:

  nmcli con modify $internal-nic connection.autoconnect=yes
  nmcli con modify $public-nic connection.autoconnect=yes

(replace enp0s3 with each of your interfaces! The host-only and internal network interfaces are the most likely to have this turned off by default.)

Connecting to your headnode

Instead of using the VirtualBox terminal, it's often much simpler to ssh in to the headnode from your native local terminal - which allows for copy-pasting, window history, etc.

Check the address of the host-only network using the ip addr command on the headnode - usually in the\24 by default.

From your host machine, open a terminal emulator, and you should be able to ssh in as root (using the password you set during install - running ssh-copy-id root@$headnode_ip is also quite useful, if you're on a Linux host machine.).

Follow the guide below from your local terminal, rather than the VirtualBox terminal. (primarily for ease of use)

Installation of the XCBC Tools and Dependencies

Please note - this is meant to be run as the root user!

0. yum install git vim bash-completion

Git is necessary for getting the playbooks; vim and bash-completion are just nice add-ons. Install your editor of choice!

1. git clone

Get the actual playbooks.

This creates a directory named CRI_XCBC in your current directory, which contains the XCBC Ansible playbooks.

2. On the headnode, from your ${HOME} directory, run ssh-keygen, to create a local set of ssh keys, followed by

cat .ssh/ >> .ssh/authorized_keys

3. cd ./CRI_XCBC and then run the script.

The script creates a python virtualenv named “ansible” in ${HOME}/ansible_env/ansible, in order to avoid polluting the system python installation. The ansible source code is cloned into ${HOME}/ansible_env/ansible_source.

Prepare your shell session

The next two steps prepare your shell for using the ansible playbooks, by source two files containing environment variables - one for a python virtualenv, and one for the local installation of ansible.

4. source ${HOME}/ansible_env/ansible/bin/activate

Loads the ansible virtualenv into the current session.

5. source ${HOME}/ansible_env/ansible_source/hacking/env-setup

Loads the ansible environment variables into the current session.

Defining Cluster Parameters

Inside the CRI_XCBC directory, examine the file group_vars/all. This file contains several important parameters for the cluster installation. The current defaults should work with the Virtualbox configuration suggested above. This is the only file that should be edited during this tutorial! Other files that would be useful or necessary to edit during a production build will be pointed out as we go along.

(The format here is - parameter_name: default_value



Separated by category, the full list of parameters is:

OpenHPC Release Version

  • openhpc_release_rpm: ""

    This contains the version number and path of the current openhpc release rpm. Older versions are listed and commented out. generate the list of these via

    curl -s | grep rpm | grep -v sles | grep -v strong | sed 's/.*="\(.*\)".*".*".*/\1/'

Headnode Information

  • public_interface: enp0s3

    The device name of the public NIC on the headnode (which provides access to the outside internet)

  • private_interface: enp0s9

    The device name of the private NIC on the headnode, which gives access to the compute nodes

  • headnode_private_ip: ""

    The ip of the headnode on the private network

  • build_kernel_ver: '3.10.0-327.el7.x86_64'

    uname -r at build time - required for Warewulf to build bootstrap images for the compute nodes. THIS SHOULD BE UPDATED AT RUN-TIME!

Private network parameters

No changes are necessary in this section. These are the default parameters used for the private network that is used to communicate with/between the compute nodes. The compute_ip parameters define the range over which the dhcp server on the headnode will offer IP addresses.

If you change the subnet here, make sure to do so consistently! The network_mask (CIDR mask) and network_long_netmask must cover the same subnet, and the compute_ip limits must fall within the same subnet.

  • private_network: ""
  • private_network_mask: "24"
  • private_network_long_netmask: ""
  • compute_ip_minimum: ""
  • compute_ip_maximum: ""

slurm.conf variables

These are added to the SLURM configuration file as needed

  • cluster_name: "xcbc-example"

    The name you’d like to give your cluster. This will be inserted into the slurm.conf file.

  • gres_types: "gpu"

    (if any GPU nodes exist) - any types of consumable resources that exist on your cluster. COMMENTED OUT BY DEFAULT - IF YOU ARE BUILDING ON A PHYSICAL SYSTEM WITH GPU NODES, UNCOMMENT THIS LINE in ${HOME}/CRI_XCBC/group_vars/all!

Stateful Node controls

  • stateful_nodes: false

    Choose whether or not you’d like to build stateful compute nodes, or go with the Warewulf default of having nodes pull down a new image each time they boot. CURRENTLY NOT IMPLEMENTED, THE DEFAULT IS FALSE.

Node Config Vars - for stateful nodes

  • sda1: "mountpoint=/boot:dev=sda1:type=ext3:size=500"
  • sda2: "dev=sda2:type=swap:size=500"
  • sda3: "mountpoint=/:dev=sda3:type=ext3:size=fill"

    These options must be defined in order for compute nodes to boot from local disk. Currently outside the scope of this tutorial.

GPU Necessities

  • nvidia_driver_installer: ""

    Contains the full name of the NVIDIA driver installer. This should be downloaded and placed in CRI_XCBC/roles/gpu_build_vnfs/files/. COMMENTED OUT BY DEFAULT - ONLY NECESSARY FOR CLUSTERS WITH GPU NODES.

Warewulf Parameters

The following should not be changed, unless you are familiar with the guts of these playbooks. They are used in defining the images for different types of compute nodes, and must have corresponding names in the directory defined by the template_path variable.

  • template_path: "/usr/libexec/warewulf/wwmkchroot/"
  • compute_template: "compute-nodes"
  • gpu_template: "gpu-nodes"
  • login_template: "login-nodes"

chroot Parameters

The following should not be changed, unless you are familiar with the guts of these playbooks and are familiar with Warewulf. These define the location and names of the chroot images for different types of compute nodes. Do not worry! If you don't have GPU or login nodes, space and time will not be wasted making unnecessary images.

  • compute_chroot_loc: "/opt/ohpc/admin/images/{{ compute_chroot }}"
  • compute_chroot: centos7-compute
  • gpu_chroot_loc: "/opt/ohpc/admin/images/{{ gpu_chroot }}"
  • gpu_chroot: centos7-gpu
  • login_chroot_loc: "/opt/ohpc/admin/images/{{ login_chroot }}"
  • login_chroot: centos7-login

Node Inventory Method

  • node_inventory_auto: true

Allows one to switch between ’manually’ adding compute node information here (in ${HOME}/CRI_XCBC/group_vars/all) or by running wwnodescan. The default is to use wwnodescan to automatically search for nodes in the network. In some situations, such as migrating an existing cluster to a new framework, one may already have a list of hardware. If some of that is owned/provided by researchers, it is necessary to keep track of 'which nodes are which', and can be beneficial to add and name nodes based on an existing set of information. The following items are ONLY to be used in this case.

- compute_nodes: 
     - { name: "compute-1", vnfs: '{{compute_chroot}}',  cpus: 1, sockets: 1, corespersocket: 1,  mac: "08:00:27:EC:E2:FF", ip: ""}

The compute_nodes variable is a list of dictionaries, each of which contains the necessary information to build and name each compute node. You will have to edit the MAC address for each node, if using the manual node inventory method.

-   login_nodes: 
     - { name: "login-1", vnfs: '{{login_chroot}}', cpus: 8, sockets: 2, corespersocket: 4,  mac: "00:26:B9:2E:23:FD", ip: ""}

List of login nodes, same format as compute_nodes

-   gpu_nodes: 
    - { name: "gpu-compute-1", vnfs: '{{gpu_chroot}}', gpus: 4, gpu_type: "gtx_TitanX", cpus: 16, sockets: 2, corespersocket: 8,  mac: "0C:B4:7C:6E:9D:4A", ip: ""}

List of gpu nodes, with the addition of a key describing the number and types of GPU available on that node. These parameters will be inserted into the slurm.conf. The gpu_type is completely custom, and is the string that users must request to run on these nodes in the default SLURM configuration.

Ansible Inventory

Note the inventory file in CRI_XCBC/inventory:

headnode ansible_host="{{ headnode_private_ip }}" ansible_connection=ssh ansible_ssh_user=root

Make sure that the hostname of your headnode matches the entry on that line! Either edit the inventory file, or change the hostname via: hostnamectl set-hostname headnode.

Configuration of the Headnode via Ansible

Examine the headnode.yml file - this contains the basic recipe for the sequence of steps to take. While it could be run all at once with ‘ansible-playbook headnode.yml‘ we will take go through it here step by step. Each step can be run with the ’-t’ flag, which asks ansible-playbook to exectute only tasks with the given name.

When running these scripts, be sure to either cd to the playbook directory (cd ${HOME}/CRI_XCBC/) or provide the complete path before each file - like ansible-playbook -i ${HOME}/CRI_XCBC/inventory/headnode -t pre_ohpc ${HOME}/CRI_XCBC/headnode.yml.

1. This first role installs necessary dependencies for the OpenHPC rpms, configures the firewall zones internal and public. This also installs fail2ban, configures the /etc/hosts file, and sets up the headnode as an ntp server for the cluster (this is IMPORTANT for SLURM functionality). This also configures ssh to disallow password authentication - if you don't want this, edit the template in roles/pre_ohpc/templates/sshd_config.j2 To apply this role, run: ansible-playbook -i inventory/headnode -t pre_ohpc headnode.yml

2. ansible-playbook -i inventory/headnode -t ohpc_install headnode.yml This second role installs several OpenHPC package groups, base, warewulf and slurm server, configures SLURM (and enables job accounting), creates a basic template for the compute nodes, and applies two fixes to the wwsh and wwnodescan scripts.

3. ansible-playbook -i inventory/headnode -t ohpc_config headnode.yml This third role configures the headnode for several things. It sets the interface that Warewulf uses, and sets up httpd to serve files to compute nodes. It configures xinetd for tftp (for PXE-booting the compute nodes), and mariadb for the internal Warewulf database. This also initializes the NFS exports from the headnode to compute nodes, in /etc/exports. There are three main exports: - /home for user home directories - /opt/ohpc/public for OpenHPC documentation and packages - `/export' for custom software packages shared to compute nodes

Installation of the compute nodes

4. ansible-playbook -i inventory/headnode -t compute_build_vnfs headnode.yml This role builds an image for the compute nodes, by configuring a chroot environment in /opt/ohpc/admin/images/centos-7.3-compute, and adding a "VNFS" image to the Warewulf database. This will be used by the compute nodes to PXE boot. It takes a while to build the image - good time to take a break from your screen!

5. ansible-playbook -i inventory/headnode -t compute_build_nodes headnode.yml This role does one of two things: if you are using the automatic inventory method, it runs wwnodescan, with names based on the number of nodes you've defined in group_vars/all, and waits for the nodes to boot. At this point, simply Start your compute nodes in VirtualBox, without providing a boot medium, and watch to be sure they receive a DHCP response. Occasionally, they will fail to receive a response, but will work fine if booted a second time.

If you are using the 'manual' method of node entry, this role will enter the provided information (again, from group_vars/all) in the Warewulf database. At that point, you may boot your compute nodes any time after the role finishes running, and they should receive a PXE boot image from the headnode as in the automatic method.

6. ansible-playbook -i inventory/headnode -t nodes_vivify headnode.yml This final role will "bring your nodes to life" by starting the necessary services on the headnode and compute nodes, such as slurmctld (on the headnode), slurmd (on the compute nodes), and munge (used by slurm on all nodes for authentication).

Testing the scheduler

After confirming that both nodes have booted successfully (In the VirtualBox windows, you should see a basic login prompt for each), double-check that you are able to ssh into the machines as root.

Now, in order to test the scheduler, it is necessary to add a user, by running useradd test-user on the headnode. To make sure the new user will be enabled on the compute node, run wwsh file sync to update the passwd,group, and shadow files in the Warewulf database, followed by pdsh -w compute-[0-1] '/warewulf/transports/http/wwgetfiles' to request that the compute nodes pull the files from the master. While they are automatically synced every 5 minutes, this will force an update immediately.

Next, become the new user, via su - test-user.

Open your text editor of choice, and create a (very) simple slurm batch file (named slurm_ex.job in this example), like:

#SBATCH -o nodes.out

srun -l /bin/hostname
srun -l /bin/pwd

Submit this to the scheduler via sbatch ./slurm_ex.job

You should receive a message like Submitted batch job 2 and find an output file called nodes.out with the contents:

[test-user@headnode ~]$ cat nodes.out 
0: compute-0
1: compute-1
0: /home/test-user
1: /home/test-user

Otherwise, there should be useful debugging information in /var/log/slurmctld on the headnode, or in /var/log/slurmd on the compute nodes.


At this point, you have a basic working cluster with scheduler. The addition of scientific software and utilities available through XSEDE will be covered in this guide soon.

Thanks for trying this out! Please get in touch with any problems, questions, or comments at, with 'XCRI XCBC Tutorial" in the subject line.