Connect to AWS API with fog.

require 'fog'

c = Fog::Compute.new(
                 :provider => 'AWS',
                 :aws_access_key_id => 'Your AWS access key',
                 :aws_secret_access_key => 'Your AWS secret key',
                 :region => 'us-east-1' )

Associate Elastic IP

eip = c.addresses.get('Your elastic IP address')
c.associate_address("Your instance id",nil,nil,eip.allocation_id)

Disassociate Elastic IP

eip = c.describe_addresses('public-ip' => ['Your elastic IP address'])
disassociate_address(nil,eip[:body]["addressesSet"][0]["associationId"])

Association Elastic IP script example.

assign_eip.rb:

#!/usr/bin/ruby
# This is a script that assign Elastic IP to current instance.
# Usage:
# You need to fill out config_eip.json config file:
# {
# "aws_access_key": "aws_access_key",
# "aws_secret_key": "aws_secret_key",
# "eip": "x.x.x.x",
# }
#
# Config file should be in the same dir as a script
# then, start script:
# assign_eip.rb
# This will assign x.x.x.x Elastic IP to current instance.

require "rubygems"
require "json"
require "net/http"
require "fog"

# Read config
CONFIG = JSON.parse(IO.read(File.join(File.dirname(__FILE__), 'assign_eip.json')))

# Here we need to get server.id
INSTANCE_HOST = '169.254.169.254'
INSTANCE_ID_URL = '/latest/meta-data/instance-id'
INSTANCE_REGION_URL = '/latest/meta-data/placement/availability-zone'

httpcall = Net::HTTP.new(INSTANCE_HOST)
resp, instance_id = httpcall.get2(INSTANCE_ID_URL)
resp, region = httpcall.get2(INSTANCE_REGION_URL)

# Cut out availability zone marker.
# For example if region == "us-east-1c" after cutting out it will be
# "us-east-1"

region = region[0..-2]

# First we get a connection object from amazon, region is
# required if your instances are in other zone than the
# gem's default one (us-east-1).

c = Fog::Compute.new(
                 :provider => 'AWS',
                 :aws_access_key_id => CONFIG['aws_access_key'],
                 :aws_secret_access_key => CONFIG['aws_secret_key'],
                 :region => region )

# Then we get Fog::Compute::AWS::Address to get allocation_id of Elastic IP.
# For some reason I failed to make it work with IP address directly.
# if I use Elastic IP instead of allocation id it always returns 400
# Bad Request.

eip = c.addresses.get(CONFIG['eip'])

# Then we accociate Elastic IP with current node.

c.associate_address(instance_id,nil,nil,eip.allocation_id)

assign_eip.json:

{
"aws_access_key": "AWS_access_key",
"aws_secret_key": "Your_AWS_secret_key",
"eip": "Elastic IP to assign"
}

Yet another one DevOps blog

Ops and DevOps stories

Manage AWS Elastic IPs with fog

Connect to AWS API with fog.

Associate Elastic IP

Disassociate Elastic IP

Association Elastic IP script example.

Further reading