How do you configure fabric to connect to remote hosts using SSH keyfiles (for example, Amazon EC2 instances)?
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.
Using an SSH keyfile with Fabric