Using an SSH keyfile with Fabric

Finding a simple fabfile with a working example of SSH keyfile usage isn’t easy for some reason. I wrote a blog post about it (with a matching gist).

Basically, the usage goes something like this:

from fabric.api import *

env.hosts = ['host.name.com']
env.user = 'user'
env.key_filename = '/path/to/keyfile.pem'

def local_uname():
    local('uname -a')

def remote_uname():
    run('uname -a')

The important part is setting the env.key_filename environment variable, so that the Paramiko configuration can look for it when connecting.

Another cool feature available as of Fabric 1.4 – Fabric now supports SSH configs.

If you already have all the SSH connection parameters in your ~/.ssh/config file, Fabric will natively support it, all you need to do is add:

env.use_ssh_config = True

at the beginning of your fabfile.

As stated above, Fabric will support .ssh/config file settings after a fashion, but using a pem file for ec2 seems to be problematic. IOW a properly setup .ssh/config file will work from the command line via ‘ssh servername’ and fail to work with ‘fab sometask’ when env.host=[‘servername’].

This was overcome by specifying the env.key_filename=’keyfile’ in my fabfile.py and duplicating the IdentityFile entry already in my .ssh/config.

This could be either Fabric or paramiko, which in my case was Fabric 1.5.3 and Paramiko 1.9.0.

For me, the following didn’t work:

env.user=["ubuntu"]
env.key_filename=['keyfile.pem']
env.hosts=["xxx-xx-xxx-xxx.ap-southeast-1.compute.amazonaws.com"]

or

fab command -i /path/to/key.pem [-H [user@]host[:port]]

However, the following did:

env.key_filename=['keyfile.pem']
env.hosts=["[email protected]"]

or

env.key_filename=['keyfileq.pem']
env.host_string="[email protected]"

I had to do this today, my .py file was as simple as possible, like the one posted in the answer of @YuvalAdam but still I kept getting prompted for a password…

Looking at the paramiko (the library used by fabric for ssh) log, I found the line:

Incompatible ssh peer (no acceptable kex algorithm)

I updated paramiko with:

sudo pip install paramiko --upgrade

And now it’s working.

For fabric2 in fabfile use the following:

from fabric import task, Connection

@task
def staging(ctx):
    ctx.name = 'staging'
    ctx.user = 'ubuntu'
    ctx.host = '192.1.1.1'
    ctx.connect_kwargs.key_filename = os.environ['ENV_VAR_POINTS_TO_PRIVATE_KEY_PATH']

@task
def do_something_remote(ctx):
    with Connection(ctx.host, ctx.user, connect_kwargs=ctx.connect_kwargs) as conn:
        conn.sudo('supervisorctl status')

and run it with:

fab staging do_something_remote

UPDATE:
For multiple hosts (one host will do also) you can use this:

from fabric2 import task, SerialGroup

@task
def staging(ctx):
    conns = SerialGroup(
        '[email protected]',
        '[email protected]',
        connect_kwargs=
        {
            'key_filename': os.environ['PRIVATE_KEY_TO_HOST']
        })
    ctx.CONNS = conns
    ctx.APP_SERVICE_NAME = 'google'

@task
def stop(ctx):
    for conn in ctx.CONNS:
        conn.sudo('supervisorctl stop ' + ctx.APP_SERVICE_NAME)

and run it with fab or fab2:

fab staging stop

None of these answers worked for me on py3.7, fabric2.5.0 and paramiko 2.7.1.

However, using the PKey attribute in the documentation does work: http://docs.fabfile.org/en/2.5/concepts/authentication.html#private-key-objects

from paramiko import RSAKey
ctx.connect_kwargs.pkey = RSAKey.from_private_key_file('path_to_your_aws_key')
with Connection(ctx.host, user, connect_kwargs=ctx.connect_kwargs) as conn:
    //etc....