How to build a Raspberry Pi cluster

These notes are based on many excellent guides, including (but not limited to):

1. Download the Raspbian image from the Raspberry Pi website.
2. Download and install Win32 Disk Imager from its SourceForge website.
3. Burn the Raspbian image to the MicroSD card using Win32 Disk Imager (I used a 32 GB MicroSD).
4. Enable SSH by creating an extension-less file named ssh in the root of the boot partition.
5. Insert the MicroSD card (with Raspbian burned on it) into the Raspberry Pi.
6. Connect a network cable from the Raspberry Pi to your router/switch (the same router your PC is connected to).
7. Connect a Micro USB cable from the Raspberry Pi to a power source.
8. Download PuTTY from its website.
9. Open a command prompt (type cmd in the Windows search box).
10. Type ping raspberrypi and hit Enter (write down your Pi’s IP address).
11. Open PuTTY, type the Pi’s IP address, and click Open.
12. The login is pi and the password is raspberry.
13. Type sudo raspi-config and hit Enter.
14. Select “Update”.
15. Expand the file system.
16. Advanced options.
17. Set the hostname to “Pi01”, or type sudo nano /etc/hostname.
18. Exit raspi-config.

sudo apt-get -y update
sudo apt-get -y upgrade
sudo apt-get -y install wolfram-engine
sudo apt-get -y install r-base

To check how much space is left on the SD card, type df -h.

The MPICH 3.2 source is at http://www.mpich.org/static/downloads/3.2/mpich-3.2.tar.gz.

sudo mkdir mpich2
cd ~/mpich2
sudo wget http://www.mpich.org/static/downloads/3.2/mpich-3.2.tar.gz
sudo tar xfz mpich-3.2.tar.gz
sudo mkdir /home/rpimpi/
sudo mkdir /home/rpimpi/mpi-install
sudo mkdir /home/pi/mpi-build
sudo apt-get -y install gfortran
sudo /home/pi/mpich2/mpich-3.2/configure -prefix=/home/rpimpi/mpi-install
sudo make
sudo make install
cd ..
nano .bashrc

Paste the following line at the bottom of the file:

PATH=$PATH:/home/rpimpi/mpi-install/bin

I also added two optional commands to .bashrc after the PATH: df -h (to show the space left on the MicroSD) and htop (to show the interactive process viewer).

Then hold CTRL and press “6” “x”, let go of CTRL, and press “y” and Enter.

sudo reboot
mpiexec -n 1 hostname

The mpi4py 2.0.0 source is at https://bitbucket.org/mpi4py/mpi4py/downloads/mpi4py-2.0.0.tar.gz.

wget https://bitbucket.org/mpi4py/mpi4py/downloads/mpi4py-2.0.0.tar.gz
sudo tar -zxf mpi4py-2.0.0.tar.gz
cd mpi4py-2.0.0
sudo apt-get -y install python-dev
python setup.py build
sudo python setup.py install
export PYTHONPATH=/home/pi/mpi4py-2.0.0
mpiexec -n 5 python demo/helloworld.py

1. Remove the MicroSD from the Raspberry Pi.
2. Create an image using Win32 Disk Imager.
3. Copy it to the other MicroSDs.
4. Insert the duplicate MicroSDs into the additional Raspberry Pi nodes.

Let’s assume that the IP addresses are:

• Pi01: 192.168.1.1
• Pi02: 192.168.1.2
• Pi03: 192.168.1.3
• Pi04: 192.168.1.4
• Pi05: 192.168.1.5
• Pi06: 192.168.1.6

Do the following for Pi02, Pi03, Pi04, Pi05, and Pi06 (the password is raspberry):

ssh pi@192.168.1.2
sudo nano /etc/hostname

or

sudo raspi-config

• Scroll down to Advanced and hit Enter.
• Scroll down to Hostname and hit Enter.
• Change the name (Pi01, Pi02, Pi03, Pi04) and hit Enter.
• Press Tab until Finish is selected, then hit Enter.

Change the IP addresses below to reflect the IP addresses of the Pi0x, and enter them in the nodes file:

nano nodes

192.168.1.1
192.168.1.2
192.168.1.3
192.168.1.4
192.168.1.5
192.168.1.6

Hold CTRL, press 6, x, press y, hit Enter (or CTRL+O and CTRL+X).

mpiexec -n 1 hostname
mpiexec -f nodes -n 6 hostname

You should get errors on the second command, because Pi01 does not have access to the other nodes. So, do the following.

From Pi01, do the following:

scp 192.168.1.2:/home/pi/.ssh/Pi02 .
cat Pi02 >> authorized_keys

scp 192.168.1.3:/home/pi/.ssh/Pi03 .
cat Pi03 >> authorized_keys

scp 192.168.1.4:/home/pi/.ssh/Pi04 .
cat Pi04 >> authorized_keys

scp 192.168.1.5:/home/pi/.ssh/Pi05 .
cat Pi05 >> authorized_keys

scp 192.168.1.6:/home/pi/.ssh/Pi06 .
cat Pi06 >> authorized_keys

1. Create the prime.py file (listed below) in /home/pi of Pi01.
2. Then copy it to the other nodes as follows:

scp prime.py 192.168.1.2:/home/pi
scp prime.py 192.168.1.3:/home/pi
scp prime.py 192.168.1.4:/home/pi
scp prime.py 192.168.1.5:/home/pi
scp prime.py 192.168.1.6:/home/pi
mpiexec -f nodes -n 4 python prime.py

Then copy primality_cluster_test1.py (see below) to all nodes, and run the following commands on Pi01:

scp primality_cluster_test1.py 192.168.1.2:/home/pi
scp primality_cluster_test1.py 192.168.1.3:/home/pi
scp primality_cluster_test1.py 192.168.1.4:/home/pi
scp primality_cluster_test1.py 192.168.1.5:/home/pi
scp primality_cluster_test1.py 192.168.1.6:/home/pi

This command runs only on node 1 (Pi01), using all four cores (-n 4). It took 7.738 seconds to find 109926 primes.

time mpiexec -n 4 python primality_cluster_test1.py

This one runs on all nodes, using all twenty-four cores (-n 24). It took 5.952 seconds to find 109926 primes. Remember that Pi01 (node 1) is a Raspberry Pi 4. When tested on Pi06 (node 6), which is a Raspberry Pi 3 v. 1.2, it took 25.4 seconds! So combining old and new versions of the Raspberry Pi may not be the ideal approach for building a cluster.

time mpiexec -hostfile nodes -n 24 python primality_cluster_test1.py

Use htop to view the processes on each node.

Copy it exactly as shown below.

def is_prime(n):
   status = True
   if n < 2:
      status = False
   else:
      for i in range(2,n):
         if n % i == 0:
            status = False
   return status
for n in range(1,101):
   if is_prime(n):
      if n==97:
         print n
      else:
         print n,",",

https://www.youtube.com/watch?v=VzcarXuVUvU&t=639s

The file primality_cluster_test1.py is here.

Some additional information by Alasdair Allan and Coobird’s Lab (Part 1, Part 2, Part 3).