a quick script to help you avoid setting up security groups using 0.0.0.0/8 for your own instances.

sg_update.rb

require 'aws-sdk'
require 'json'
require 'open-uri'

# Lets get our IP first
ip = JSON.parse(open('http://jsonip.com').string)['ip'] + '/32'

# You'll need to provide details that allow for API access to SG's. 
ACCOUNT = {
      :access_key_id => '',
      :secret_access_key => '',
      :region => 'eu-west-1'
}

# take it as an argument or provide a default value
SG = ARGV[0] || 'sg-xyz'
AWS.config(access_key_id: ACCOUNT[:access_key_id], secret_access_key: ACCOUNT[:secret_access_key] , region: ACCOUNT[:region])
ec2 = AWS::EC2.new

# This bit lets us determine if it's a security group name or a security group id.
if /sg-\w+/.match(SG).nil?
  sg = ec2.security_groups.filter('group-name',SG).first

  if sg.nil?
    abort("The security group %s doesn't exist therefore we are unable to continue" % SG)
  end

else
  sg = ec2.security_groups[SG]

  if not sg.exists?
    abort("The security group %s doesn't exist therefore we are unable to continue" % SG)
  end

end


sg.ingress_ip_permissions.each do |ip_rule|
  # Add a new rule based on the old one
  begin
    sg.authorize_ingress(ip_rule.protocol, ip_rule.port_range, ip)
    puts "Adding rule to allow %s to connect on %s" % [ip,ip_rule.port_range]
  rescue AWS::EC2::Errors::InvalidPermission::Duplicate
    # This is for when you do it but your IP hasn't changed. Prevents unwanted errors/crashes.
    next
  end

  # out with the old!
  ip_rule.revoke
end