How to s3 object URL that works with cloudfront? - ruby-on-rails

Question

I'm currently storing files privately on S3. In my Rails app, in the attachment.rb model I can obtain a public URL for the private file like so:
def cdn_url ( style='original' )
attachment.s3_object(style).url_for( :read, secure: true, response_content_type: self.meta['file_content_type'], expires: 1.hour ).to_s
end
The problem is this is providing a URL to S3 and rewriting the URL to use my Cloudfront origin url is erroring with:
The request signature we calculated does not match the signature you provided. Check your key and signing method.
How can I get a public URL asset like below but serve the asset via Cloudfront?

Answer 1

First Way (Easy)
Just use aws_cf_signer gem. Put it in you bundler.
WIth this you can do something like
def cdn_url (options = {})
style = options[:style] || 'original'
cloudfront_domain = options[:cloudfront_domain] || 'example.cloudfront.net'
cloudfront_pem_key_path = options[:cloudfront_pem_key_path]
cloudfront_key_paid_id = options[:cloundfrount_key_paid_id]
path = attachment.path(style) #path of the file
# you can get this values from your aws a/c , most probably by going int
# https://console.aws.amazon.com/iam/home?#security_credential
signer = AwsCfSigner.new(cloudfront_pem_key_path, cloudfront_key_paid_id)
# this configuration may vary.
# visit https://github.com/dylanvaughn/aws_cf_signer
# and check all available settings/options
url = signer.sign(path, :ending => Time.now + 3600)
cloudfront_domain + url
end
With this you can access the url with something like this
cdn_url(cloudfront_pem_key_path: '/users/downloads/pri.pem' , cloudfront_key_paid_id: '33243424XXX')
Second way
# A simple function to return a signed, expiring url for Amazon Cloudfront.
# This will require openssl, digest/sha1, base64 and maybe other libraries.
module CloudFront
def get_signed_expiring_url(domain,path, expires_in, private_key_filename, key_pair_id)
# AWS works on UTC, so make sure you are not using local time
expires = (Time.now.getutc + expires_in).to_i.to_s
private_key = OpenSSL::PKey::RSA.new(File.read(private_key_filename))
# path should be your S3 path without a leading slash and without a file extension.
# e.g. files/private/52
policy = %Q[{"Statement":[{"Resource":"#{path}","Condition":{"DateLessThan":{"AWS:EpochTime":#{expires}}}}]}]
signature = Base64.strict_encode64(private_key.sign(OpenSSL::Digest::SHA1.new, policy))
# I'm not sure exactly why this is required, but it's in Amazon's perl script and seems necessary
# Different base64 implementations maybe?
signature.tr!("+=/", "-_~")
"#{domain}#{path}?Expires=#{expires}&Signature=#{signature}&Key-Pair-Id=#{key_pair_id}"
end
end
With this you can do something like
def cdn_url ( style='original',cloudfront_pem_key_path,key_pair_id)
path = attachment.path(style) #path of the file
# you can get this values from your aws a/c , most probably by going int
CloudFront.get_signed_expiring_url 'example.cloudfront.net', path, 45.seconds ,'/users/downloads/pri.pem', 'as12XXXXX')
end
Give a try, may be it will work. Be sure to properly set properly bucket access policy. check this out if you are seeing accessDenied error http://www.jppinto.com/2011/12/access-denied-to-file-amazon-s3-bucket/

Answer 2

Use the aws sdk gem.
See the API Documentation
Details about generating a presigned URL for an operation on the object
Provide the access-key-id and secret-access-key:-
S3 = AWS::S3.new(
:access_key_id => 'access_key_id',
:secret_access_key => 'secret_access_key')
In controller put these lines:--
bucket = S3.buckets['bucket_name']
s3_obj = bucket.objects["Path-to-file"]
return s3_obj.url_for(:read, :expires => 60*60).to_s
This link will expires in 1 Hour. After that the link will be not accessible.