Because Hadoop requires communication between multiple processes on one or more
machines, we need to ensure that the user we are using for Hadoop can connect to each
required host without needing a password. We do this by creating a Secure Shell (SSH) key
pair that has an empty passphrase. We use the ssh-keygen command to start this process
and accept the offered defaults.
Once we create the key pair, we need to add the new public key to the stored list of trusted
keys; this means that when trying to connect to this machine, the public key will be trusted.
After doing so, we use the ssh command to connect to the local machine and should expect
to get a warning about trusting the host certificate as just shown. After confirming this, we
should then be able to connect without further passwords or prompts.
