SSH into an EC2 instance by name.

ec2-ssh.rb

#!/usr/bin/env ruby

instance_name = ARGV[0]
abort "Please specify an instance name" unless instance_name and instance_name.length > 0

instance_info, selected_instance = {}, nil
info_keymap = {2 => :ami_id, 3 => :address, 5 => :status, 6 => :keypair_name}

instances = `ec2-describe-instances`.split("\n").map{|l| l.split("\t")}
instances.each do |line|
  case line.first
  when 'INSTANCE'
    keys = info_keymap.keys
    instance_id = line[1]
    this_instance = Hash[*info_keymap.values_at(*keys).zip(line.values_at(*keys)).flatten]
    instance_info[instance_id] = this_instance
  when 'TAG'
    if line[1] == 'instance' and line[3] == 'Name'
      selected_instance = line[2] if line[4] == instance_name
    end
  end
end

abort "No instance named #{instance_name}!" unless selected_instance

instance = instance_info[selected_instance]
abort "Instance is not running!" unless instance[:status] == 'running'

instance_address = instance[:address]
keypair_name = instance[:keypair_name]

ec2_home = `echo $EC2_HOME`.chomp
keyfile = "#{ec2_home}/#{keypair_name}.pem"
abort "No private key matching '#{keypair_name}' found in #{ec2_home}!" unless File.exists? keyfile

exec "ssh -i #{keyfile} -l ec2-user #{instance_address}"