Easier EC2 Logins

With the addition of the new Northern California region to EC2 I ran into a problem: I had too many keys in my SSH Agent. To fix it I came up with the (somewhat imperfect) solution of removing the EC2 keys from my SSH Agent and moving the logic to the ssh config file; I’ve also written some regular expressions that pick the key automatically based on the hostname (or, if you’re using IPs, imperfectly matches the EC2 subnets).

This solution also skips hostkey checking since our instances have a maximum life of a few hours so there’s no point keeping the old hostkey fingerprints around.

Here’s an excerpt from my .ssh/config file

# Default params  
Host *  
    HashKnownHosts no  
    StrictHostKeyChecking no  
    ConnectTimeout 15  
    ForwardAgent yes  
    RSAAuthentication yes  
    PasswordAuthentication yes  
    HostBasedAuthentication no  
    ForwardX11 yes  
  
#  
# Amazon EC2 hosts  
#               
  
# EC2 Northern Virginia  
#  216.182.224.0/20  
#  72.44.32.0/19     
#  67.202.0.0/18     
#  75.101.128.0/17   
#  174.129.0.0/16    
#  204.236.224.0/19  
Host *.compute-1.amazonaws.com 174.129.* 204.236.2[23]?.* 67.202.* 75.101.[12]??.* 216.182.2[23]?.* 72.44.[3456]?.*  
    User root  
    CheckHostIP no  
    IdentityFile ~/.keys/ssh/ec2/us_east_1.key  
    StrictHostKeyChecking no  
    UserKnownHostsFile /dev/null  
    IdentitiesOnly yes  
    ForwardAgent no  
  
# EC2 Northern California:  
#  204.236.128.0/18  
Host *.us-west-1.compute.amazonaws.com 204.236.1??.*  
    User root  
    CheckHostIP no  
    IdentityFile ~/.keys/ssh/ec2/us_west_1.key  
    StrictHostKeyChecking no  
    UserKnownHostsFile /dev/null  
    IdentitiesOnly yes  
    ForwardAgent no  
  
# EC2 Ireland:  
#  79.125.0.0/17  
Host *.eu-west-1.compute.amazonaws.com 79.125.?.* 79.125.??.* 79.125.1[012]?.*  
    User root  
    CheckHostIP no  
    IdentityFile ~/.keys/ssh/ec2/eu_west_1.key  
    StrictHostKeyChecking no  
    UserKnownHostsFile /dev/null  
    IdentitiesOnly yes  
    ForwardAgent no