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Raspberry-Pi based Akka Cluster workshop preparation instructions

In case you're attending a Raspberry-Pi based Akka Cluster workshop, you will need to prepare your laptop to integrate with a pre-installed 5-node cluster you'll be working on.

The following sections give instructions on how to achieve this.

Adding the cluster nodes to /etc/hosts

On your Mac, add the following entries to your /etc/hosts file:

# Cluster #0
192.168.200.10 node-0
192.168.200.11 node-1
192.168.200.12 node-2
192.168.200.13 node-3
192.168.200.14 node-4

Configure password-less login

Next, we set-up password-less login (unless your ssh remembers your password, in which case you can skip this step). We assume that we want to log in to account akkapi on a Raspberry Pi node from an account (userxxx) on your laptop. In order to set-up password-less login, you need a so-called public/private key pair. If you're unfamiliar with this concept, or don't have such a key pair, first read the paragraph titled Generating a public/private key pair in the Addendum.

Now, proceed by create a .ssh folder on the akkapi's home folder on the Pi and copy the public key (id_rsa.pub) to a file named authorized_keys in the .ssh folder. You will have to supply the password for the akkapi account for the two commands launched. On your laptop:

[Pi-Akka-Cluster git:(master) ✗ for node in 0 1 2 3 4;do ssh akkapi@node-${node} mkdir -p .ssh; done
akkapi@node-0's password:

Copy the contents of your public key to the authorized_keys file:

Pi-Akka-Cluster git:(master) ✗ for node in 0 1 2 3 4;do cat ~/.ssh/id_rsa.pub | ssh akkapi@node-${node} 'cat >> .ssh/authorized_keys'; done
akkapi@node-0's password:

With this, you should now be able to log into the akkapi on all nodes from the userxxx account on your laptop without having to enter a password.

Finish the configuration by running the updateScripts command:

Pi-Akka-Cluster git:(master) ✗ ./updatePiScripts
Copy  to node-0
run                                         100% 1104   450.3KB/s   00:00
librpi_ws281x.so                            100%   92KB   6.4MB/s   00:00
setLedType                                  100%  110    32.1KB/s   00:00
docker-compose.yml                          100% 1136    76.1KB/s   00:00
runDocker                                   100%   98    61.0KB/s   00:00
Copy  to node-1
.
.
.

Addendum

Generating a public/private key pair

We assume that we want to log in to account akkapi on a pi from an account (userxxx) on your laptop.

First, we need a pair of authentication keys on the laptop. If these keys have been generated already we can skip the generation of a new pair of authentication keys. If this isn't the case, generate them.

Logged-in on your laptop account, generate a key pair:

$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/userxxx/.ssh/id_rsa): 
Created directory '/home/userxxx/.ssh'.
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/userxxx/.ssh/id_rsa.
Your public key has been saved in /home/userxxx/.ssh/id_rsa.pub.
The key fingerprint is:
3e:4f:05:79:3a:9f:96:7c:3b:ad:e9:58:37:bc:37:e4 userxxx@A

Use an empty passphrase (just hit Enter)

As can be seen from the output generated by ssh-keygen, a pair of files (id_rsa and id_rsa.pub) are created in the (hidden) folder .ssh in the users home folder.

Let's have a look:

$ ls -l ~/.ssh
total 56
-rw-------  1 ericloots  staff   3326 Dec 21  2015 id_rsa
-rw-r--r--  1 ericloots  staff    746 Dec 21  2015 id_rsa.pub

SSH client-side configuration options

Additionally you can apply host specific options in ~/.ssh/config, which is the client-side configuration file located in the user's home directory. This file is not created by default. It is safe to create it now with the below command. Altenatively use a text editor to add the node-* (wildcarded) Host section (only the 5 indented lines).

This way you can define custom connection options, and change the username, keyfile or setup more permissive host key checking.

$ cat <<HERE >> ~/.ssh/config
    Host node-*
      User akkapi
      IdentityFile /Users/userxxx/.ssh/id_rsa
      StrictHostKeyChecking no
      UserKnownHostsFile=/dev/null
HERE
$

Essentialy SSH checks for each defintion, and if it matches the hostname value given on the command line, it applies the configurations found in the matching section.

Let's try the login with SSH client-side configurations:

$ ssh node-0
Linux node-0 4.14.98-v7+ #1200 SMP Tue Feb 12 20:27:48 GMT 2019 armv7l

HypriotOS/armv7: akkapi@node-0 in ~
$