Manage SSH Key Pairs for Cloud Servers with python-novaclient

By | February 1, 2015

The SSH protocol for remotely connecting to servers supports the use of key pairs in place of password-based logins. The private key is stored on the machine initiating the connection (usually a workstation), and the public key is stored in a user account on the remote server. When a connection is attempted, the public and private keys are used together to authenticate the user.

Key-pair authentication is more secure than password-based authentication. If you regularly connect from the same machines, disabling password-based authentication via SSH and allowing only key pair authentication protects your server from brute-force login attempts.

For more information about using SSH to connect to servers, see the following articles:

This article discusses using the python-novaclient command-line tool to generate a key pair and assign its public key to a Linux server when the server is created.


Prepare python-novaclient

The instructions in this article assume that the python-nova client is installed and configured for use with Cloud Servers. You can find detailed instructions for setting up the client in Using python-novaclient with the Rackspace Cloud.

Create a Key Pair

The python-nova client’s key pair support allows you to create or upload an existing key pair and associate it with a name you can then reference in build operations.

You can create a new key pair by using the keypair-add command for nova. You pass a name for the key pair as an argument. The public key is then stored in your user profile via the API. The output of the command is the private key.

For example, to create a key pair named “mykey” and output it to a file in the current user’s .ssh directory, you can run:

nova keypair-add mykey > ~/.ssh/webserver_rsa

Note that you can give the key file any name that you like and put it wherever you like, so long as you can find it later. If you generate multiple keys for different servers, it can be convenient to name the key files after the servers.

Only the public key is stored in your profile. If you lose the private key you must generate a new key pair.

Upload an Existing Key

If you already have a generated key pair, you can add the public key to your profile by using the keypair-add command for nova with the --pub-key option, as shown in the following example:

nova keypair-add --pub-key mykey

List Keys

To list the keys associated with your profile, use the keypair-list command for nova.

nova keypair-list

Show Key Details

To see details about a particular public key in your list, use the keypair-show command for nova and reference the name that you assigned the key pair.

nova keypair-show mykey

You can use this command to retrieve your public key for use with another server.

Delete Key

To remove a public key from your profile, use the keypair-delete command for nova and reference the name that you assigned the key pair.

nova keypair-delete mykey

Create a Server with an Injected Key

To create a server the includes a stored public key for the root user, use the boot server creation command with the –key-name argument.

nova boot --flavor performance1-1 --image <image-id> --key-name mykey Test_Server

The command’s response shows your server information, including a “key_name: mykey” field showing you what key is associated with that server.

Connect with a Key Pair

After a server is created with a key pair is up and running, you can log in by using that key pair.

On Linux and Mac, you can add your private key to your user account’s .ssh directory, then name your server via the ~/.ssh/config file:

Host myservername
User myuser
HostName myServerDnsOrIp
IdentityFile /path/to/appropriate/ssh/rsa/private/key 

Or, you can use the -i option for ssh to identify the private key for a connection. For example:

ssh -i ~/.ssh/webserver_rsa [email protected]

Key Pairs and Role-Based Access Control

Key pairs are stored for users and not for accounts. A user configured on an account cannot see or manipulate the keys of other users on the account, regardless of the role assigned to that user.

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