Hybrid cluster

May 03, 2018


Networking commodity hardware to achieve higher performance is called a Beowulf cluster. These instructions were created in 2017, and are out of date.

The components available during training events includes single-board and system-on-a-chip machines.

Jetson TX2NVIDIA1299192.168.001.105
Raspberry Pi 3BRaspbian460192.168.001.100-4
USB power, 10-portSabrent129n/a
Micro USB cables, 3’Sabrent62n/a
WL-520GU routerASUS430192.168.001.001
Gigabit switchNetgear150192.168.001.138
CAT5 cableAmazon102n/a
HDMI monitor, 7”SunFounder160n/a
HDMI cable, 15’Amazon110n/a
Wireless keyboardRii128n/a

The Jetson TX2 has multiple CPUs, and a pretty serious GPU for accelerating jobs and video rendering. Raspberry Pi make passable servers, even for websites.


The cluster is accessed by secure shell through a wireless local area network (WLAN). The WL-520GU router is flashed with Tomato firmware to act as a managed switch. Another open source alternative is DD-WRT.

The router can be restored if something goes wrong.

Navigating to IP address with username and password “admin”.

Here MAC addresses of various components can be assigned static IP addresses to make addressing easier. It can also do name addressing with DNS.

The switch interface is then accessed by navigating to a common gateway interface (CGI) at The default password is “password”.

Headless access


The nodes will only be accessed as headless servers, so you may as well use the Raspbian Lite operating system. It is 1GB smaller, and doesn’t come with bloatware. Download the image, and flash it to an SD card with Etcher. Drag and drop, super simple.

To enable ssh by default, mount the SD card (diskutil on macOS), then touch /Volumes/boot/ssh. Remove the disk,Connect the RPi to ethernet, insert the disk, and power on.

Whether the machine you need to configured is on the local network or Internet, use ssh user@hostname to log in the first time with a password. RPi come pre-configured with the user pi and password raspberry.

Find the IP address from the network admin interface, and ssh into it. If you are connecting one at a time, you can use the raspberrypi.local broadcast hostname. Or assign static IPs from the router.

Once you are in, run sudo raspi-config to enter setup mode, and do three things:

  • change the password
  • change the hostname
  • configure wireless

For security you can disable WiFi and Bluetooth by editing /boot/config.txt to include dtoverlay=pi3-disable-wifi and dtoverlay=pi3-disable-bt (respectively). Save the file and reboot.

To enable wireless, comment out the line and reboot. If something is amiss, you can systemctl enable dhcpcd.service to start the DHCP client.

You can also overclock by editing this file (e.g. arm_freq=800).

If you opted for the full Raspbian experience, you can clear unnecessary packages:

git clone git://github.com/raspberrycoulis/remove-bloat.git
sudo chmod +x ./remove-bloat/remove-bloat.sh
sudo ./remove-bloat/remove-bloat.sh

Digital Ocean

On Digital Ocean, log in as root using the supplied password with ssh root@hostname, and complete the prompts to set a new Unix password.

Users and privilege

The first time you log in, also setup a new user account with sudo useradd user.

Use the -M flag to not add a home directory.

Then choose a strong password, and add it with sudo passwd user.

The user can be given sudo privileges with gpasswd -a user sudo.

Generating keys

Next up is enabling password-less access. On your machine (the client) generate a key and copy it to the server.

ssh-keygen -t rsa
ssh-copy-id user@hostname

For greater security, you would normally disable root access by adding PermitRootLogin no to the /etc/ssh/sshd_config file, and restarting the service sudo systemctl reload sshd.service

Package installation

The apt-get package manager gets registered distributions from public repositories and install them on your system.

Before installing anything new, update the registry and already installed software with,

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install rsync build-essential manpages-dev gfortran nfs-common nfs-kernel-server vim openmpi-bin libopenmpi-dev openmpi-doc keychain nmap xinetd tftpd tftp libgdal-dev mono-runtime xsel xclip libxml2-dev libxslt-dev cython

Raspberry Pi

Network file storage

On the designated head node, you can create a root directory and make it mountable for other nodes in the cluster

mkdir /export
chown pi:pi /export/
nano /etc/fstab

Add hostname:/export /export nfs defaults,rw,exec 0 0, then edit /etc/rc.local to include the lines sleep 5 and mount -a. Restart the service,

rpcbind start
update-rc.d rpcbind enable

Remote boot image

Each device can also boot from the same image, over the network. This means only a single image needs to be configured.

To set up a second node to boot from the main node:

echo program_usb_boot_mode=1 | tee -a /boot/config.txt
mkdir -p /nfs/client1
rsync -xa --progress --exclude /nfs / /nfs/client1

Manage remotely

Remot3.it is a way to manage a lot of remote computers through a centralized web interface.

VNC can also be used, and is installed on the RPi by default, but is targeted toward desktop users.

Each computer will need to set up following these directions. The release version can be displayed with cat /etc/os-release.

If you have things setup to be command line only, and need to get to the desktop GUI to configure connections, use startx.

Update references with apt-get update.

apt-get install weavedconnectd

Attach to your account, and create ssh services.

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