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SSH keys

What are SSH keys?

When accessing Ubuntu ( or any Linux) servers, you will need to enter the username and password for every SSH session. When performing automated tasks, this can be a challenge. SSH keys can be used to improve this process. For our next tool Ansible ssh keys are required.

How SSH keys work?

The concept of SSH keys involve private and public keys.

Private keys

  • are meant to be kept a secret not shared
  • best to put a complex password on the private key.
  • are stored in the /.ssh/ folder from where the ssh client is accessed.

Public keys

  • are meant to be shared and are usually copied to the servers that are usually accessed.

run the command ssh-keygen on alpine1.

This will create 2 files , ubuntu-k3s-sshkey.pub -public key and ubuntu-k3s-sshkey private key . The filename can be set at the prompt. Ensure the full path is entered /root/.ssh/ubuntu-k3s-sshkey

alpine1:~# ssh-keygen

Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): /root/.ssh/ubuntu-k3s-sshkey
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/ubuntu-k3s-sshkey
Your public key has been saved in /root/.ssh/ubuntu-k3s-sshkey.pub
The key fingerprint is:
SHA256:Od1Wxp2mpTJ5YnLD7NShCJc+Y41YIlNLn2enjGZIxzU root@alpine1
The key's randomart image is:

Copy ssh keys to remote servers.

Once the key pair is generated, copy the public key to the remote Ubuntu server

The following script copies the ssh public key to the remote servers master1 master2 master3 worker1 worker2 worker3 xsinglenode

This script can be found in

/srv/ansible/copy-ssh-key.sh

#From /srv/ansible/ on ansible1
chmod +x copy-ssh-key.sh

#Run script 
./copy-ssh-key.sh

SSH keys are now copied to the servers.

#### Passphrase

When connecting using ssh keys, the prompt for the ssh key passphrase will be prompted for each ssh session. You can use the ssh-agent to store this passphrase

# start ssh-agent. 
eval $(ssh-agent) 

# add the private key using ssh-add, the passphrase will be prompted and not required to manually enter 
ssh-add /root/.ssh/ubuntu-k3s-sshkey

The following script adds passphrase to ssh-agent for use by ansible when connecting to remote servers

add-passphrase.sh

#kill all ssh-agent currently running
killall ssh-agent

# check if ssh-agent is running. 
eval $(ssh-agent) 

# add the private key using ssh-add, the passphrase will be prompted and not required to manually enter 
ssh-add /root/.ssh/ubuntu-k3s-sshkey

# list keys in memory
ssh-add -l

Troubleshooting

  1. Each terminal opened must be setup to use the ssh-agent
  2. Ensure only one instance of ssh-agent is running. You can run the following to terminate all ssh-agent and start a new single instance.
killall ssh-agent
  1. Check existing ssh-agent that are running. 
ps aux | grep ssh