Cloudinary Blog

Reduce Website Load Time With Multiple CDN Sub-Domains

Reduce Website Load Time With Multiple CDN Sub-Domains
UPDATE (Jul 2018):  
The information in this blog post was relevant and value at the time of publishing. However, multiple subdomains is no longer necessary now that Cloudinary delivers via HTTP/2 and it can actually degrade the performance of your site. Therefore, use of this option is no longer recommended.

OpinionStage is a wonderful service. It allows everybody a better, more engaging way to express and debate their views. OpinionStage is also one of Cloudinary's early adopters. Over time, our friends at OpinionStage helped us improve Cloudinary with many constructive suggestions.
 
If you take a look at the home page of OpinionStage you would notice that it has many small profile pictures of users that recently participated in debates and expressed their opinions. There are about 60 different user thumbnails in the home page of OpinionStage alone. There are also plenty of additional dynamic and static images in this page.
 
OpinionStage
 
Using Cloudinary, all of these images are smartly fetched from Facebook, resized and delivered through a CDN. However, there is still a potential performance issue here. Even after utilizing the fastest CDN, downloading 60 images is still a lengthy process. The browser will take a significant time to fetch them all, and result in a poor user experience. This might also compromise your search engine rank and hurt SEO effectiveness due to slower browsing speed ranking by services such as Google PageSpeed.
 
The reason for this slowness is that most modern browsers limit the number of simultaneous requests from a single remote host name while loading a web page. The limit in browsers like Chrome, Firefox and IE is 6 concurrent downloads from the same domain. The purpose of this limit is to avoid overloading the remote server with concurrent requests, but this same policy might harm user experience.
 
For example, downloading 60 images from a single host assuming 100ms for a single image download, will require 10 sequential batches of six image downloads in each and will take an overall of one whole second.
 
The following chart illustrates the performance delay of downloading many small images. Notice how slanted the asset loading chart is:
 
Chart
 
A delay of one second is definitely a lot for your users and search engines crawlers to wait for, and if the images are larger, the delay might be much longer. For a website, this may result in a reduced conversion rate and follow with a reduced income.
 
Fortunately, there are several ways to solve this performance issue. In this post we wanted to describe one of the solutions and how Cloudinary seamlessly supports it.
 

Multiple CDN sub-domains

We know that our system and the CDN we use (Akamai and AWS CloudFront) can handle many concurrent connections. Therefore we can use multiple sub-domains for the images displayed in each web page. In a way, this tells the browser that this website will not be overloaded by concurrent requests, and will allow assets to be retrieved faster. 
 
For example, if your standard Cloudinary URL for embedding an uploaded image is the following:
 
 
You can simply add to the 'a1.' prefix to the host name part of the URL. For the browser, this image is retrieved from a different host, and can be retrieved in parallel to others.
 
 
Cloudinary supports five different hostnames, 'a1' through 'a5' as a prefix to the host name. This number was selected because 30 is the global max concurrent connections of most modern browsers, and this equals 5 hostnames times 6 connections per host.
 
Back to our previous example, downloading the same 60 images can now be performed from five different hostnames simultaneously. Your visitor browsers can now retrieve 30 images simultaneously instead of just 6. This will result in a five times (80%) speed improvement over the single host method. Not bad at all.
 

Consistent sub-domain usage

You should not randomly add 'a1'-'a5' prefixes to images in your web site. Doing so might do more harm than good to your performance - a certain image is probably displayed multiple times in your web page and site. Referencing a certain image once from 'a1' and then again from 'a2' will bypass browser caching and will force downloading the image twice. Therefore, you should ensure that an image always use the same 'aX' host name. Cloudinary uses a simple CRC32 code for mapping the ID of an image to 'a1'-'a5' consistently.
 
If you are using our Ruby GEM for Ruby on Rails integration, simply set :cdn_subdomain to true either in your cloudinary.yml or in your cl_image_tag calls. Any call to cl_image_tag will calculate and attach the correct subdomain.
 
For example, the following view helper call would automatically generate a URL with a CDN subdomain if 'cdn_domain' is set to 'true':
Copy to clipboard
<%= cl_image_tag("sample.jpg", :width => 100, :height => 100,
                 :crop => :fill) %>

https://a2.res.cloudinary.com/demo/image/upload/sample.jpg
 
Same goes for when using our jQuery plugin. Simply enable CDN subdomain and all URLs would automatically have the correctly calculated prefix:
Copy to clipboard
$.cloudinary.config("cdn_subdomain", true);
Note: CDN sub-domains for secure HTTPS URLs are currently not supported due to limitations of the CDN layer.
UPDATE: HTTPS support was added as well. See details at the end of this post.
 
Why don’t you try it out? If you already have a Cloudinary account, make sure you use our latest Ruby GEM, edit your cloudinary.yml and see it in action. Click here to create a new account if you haven’t already done it.
 
For other methods to improve your website’s performance, make sure you subscribe to our feed and like our Facebook page.
 
 
UPDATE (Feb 2015): Multiple sub-domain URL convention was changed to res-X.cloudinary.com (res-1, res-2, res-3, res-4, res-5) instead of the a1-a5 prefix, which is still supported for backward compatiblity. In addition, HTTPS sub-domain support was added using the new res-X prefix convention. Cloudinary's client libraries were updated to automatically build HTTP and HTTPS URLs of the updated convention. Sample URLs:
 
 

Multi-CDN

UPDATE (Jan 2018): Readers of this post may be interested to know that Cloudinary has since launched another innovative CDN feature: Multi-CDN. Cloudinary now helps you optimize your resources to deliver maximum quality in minimum time. We now provide dynamic multi-CDN switching and smart CDN selection to ensure each user gets the CDN that will deliver content the fastest, given their location and network parameters. 
 
 

Recent Blog Posts

Create Lightweight Sites With Low-Code and No-Code Technology

Consumers expect modern websites to be mainly visual. But, the more compelling and complex the related media is, the more data is involved, compounding the site’s weight. In today’s content-craving world, delivering unoptimized media can cost you because it leads to sluggish page loads, resulting in visitors abandoning your site in search of a faster alternative. In fact, a page load that takes more than three seconds can cause as many as 40% of your visitors to bounce. Given this competitive, digital-first environment, you can’t afford to lose page views, for time is of the essence.

Read more
A Blueprint for AWS-Secured Webhook Listeners for Cloudinary

tl;dr: An AWS-secured and optimized Cloudinary webhook listener for extending the Cloudinary service

Code: Github

A webhook is a communication medium for sending notifications from one platform to another about events that occurred. In place are user-defined HTTP callbacks that are triggered by specific events. When a triggered event takes place on the source site, the webhook listens to the event, collects the data, and sends it to the URL you specified in the form of an HTTP request.

Read more
New Accessibility Features for Cloudinary’s Product Gallery Widget

Cloudinary’s Product Gallery widget, which launched in 2019, has enabled many brands to effectively and efficiently showcase their products in a sleek and captivating manner, saving countless hours of development time and accelerating release cycles. By adding Cloudinary’s Product Gallery widget with its customizable UI to their product page, retailers reap numerous benefits, often turning visitors into customers in short order.

Read more
Why Successful Businesses Engage With and Convert Audiences With Visual Media

Most business buyers prefer to research purchase options online, as do many shoppers. No wonder online retail sales in the U.S. rose by 32.4% in 2020—an impressive gain of $105 billion.

For B2B and B2C businesses, text-heavy websites are no longer adequate in attracting shoppers. Instead, engaging visual media—spin images, videos, 3D models, augmented reality—are becoming a must for conveying eye-catching details and differentiators about products or services.

Read more
Making User-Generated Content (UGC) Shoppable With Cloudinary

User-generated content (UGC) is a powerful marketing tool. Not only does video complement marketing efforts for e-commerce by enabling customers to explore products in greater detail, but UGC also adds an element of trust. As a bonus, user-generated video is an exceptional opportunity for e-businesses to attract website traffic without their marketing team having to create promotional videos from scratch. User-generated content drives conversions and brand loyalty as a direct result of authentic interaction.

Read more