How to use $remote_addr with rails and nginx secure_link - ruby-on-rails

Question

I have a rails application that makes calls to another server via net::http to retrieve documents.
I have set up Nginx with secure_link.
The nginx config has
secure_link $arg_md5,$arg_expires;
secure_link_md5 "$secure_link_expires$uri$remote_addr mySecretCode";
On the client side (which is in fact my rails server) I have to create the secure url something like:
time = (Time.now + 5.minute).to_i
hmac = Digest::MD5.base64digest("#{time}/#{file_path}#{IP_ADDRESS} mySecretCode").tr("+/","-_").gsub("==",'')
return "#{DOCUMENT_BASE_URL}/#{file_path}?md5=#{hmac}&expires=#{time}"
What I want to know is the best way to get the value above for IP_ADDRESS

Answer 1

There are multiple answers in SO on how to get the ip address but alot of them do not seem as reliable as actually making a request to a web service that returns the ip address of the request as this is what the nginx secure link will see (we don't want some sort of localhost address).
I put the following method on my staging server:
def get_client_ip
data=Hash.new
begin
data[:ip_address]=request.ip
data[:error]=nil
rescue Exception =>ex
data[:error]=ex.message
end
render :json=>data
end
I then called the method from the requesting server:
response = Net::HTTP.get_response(URI("myserver.com/web_service/get_client_ip"))
if response.class==Net::HTTPOK
response_hash=JSON.parse response.body
ip=response_hash["ip_address"] unless response_hash[:error]
else
#deal with error
end
After getting the ip address successfully I just cached it and did not keep on calling the web service method.