If you’re storing files in Azure Storage, you’ll likely soon find that the cost of bandwidth will soon become one of the more expensive items in your Azure bill. By using a content delivery network (CDN), you can improve performance for those accessing your files from around the world, while also reducing the bandwidth costs incurred on Azure.

Microsoft offers its own Azure CDN solution, or you can use Akamai or Verizon. However, for the purposes of this tutorial we’ll be using Cloudflare - a third-party vendor who offers a free tier that should meet most people’s needs. Cloudflare can cache files based on the caching headers you apply when you upload files to blob storage, or you can apply default caching values. As a side note, Cloudflare also offers other services such as DDoS protection and edge workers.

Note that you’lll need to have your own domain name for this to work - you need to associate a custom domain name with the blob storage account. To use Cloudflare services, you also need to point your domain to Cloudflare’s name servers.

Setup Cloudflare
If you have a Cloudflare account already, you can skip this section. Otherwise, create an account at Cloudflare. The free account will be fine for this tutorial.

Once your account has been created, click “Add a site” and follow the instructions to verify and add your domain to Cloudflare. If you want to use a sub domain (eg. cdn.example.com) for the Blob Storage custom domain, this should be the root domain (eg. example.com).

This will also require changing your domain’s nameservers, so you’ll require admin permissions with your DNS registrar.

Getting started
If you haven’t already done so, create an Azure Storage resource by clicking “Create a resource” in the Azure Portal. Search for “storage account”, and choose the Microsoft service by clicking “Create”. Fill in the settings as required for your storage account.

Once your account has been provisioned, head to the “Storage accounts” tab and choose the account you want to setup.

Create a custom domain
The first step in setting up Cloudflare with Blob Storage is to map it to a custom domain name that you own (such as example.com). In the Azure Portal for your storage account, go to “Custom domain” under the “Blob service” tab.

You should see some Microsoft instructions about configuring a CNAME record with your DNS provider, which should now be Cloudflare. Follow these steps first, by logging into your Cloudflare account and adding the CNAME record to validate your ownership of the domain with Microsoft. Note that this will be the URL that people will see and use when accessing your content, so CNAMEs such as cdn.example.com or static.example.com are commonly used.

In Cloudflare, make sure the proxy status for your domain or subdomain is set to DNS only. If proxied is enabled, verification with Microsoft will fail.

Once you’ve added the required record to your domain name, enter the URL in the text field below in the Azure Portal. Click “Save”, and if the DNS changes have propogated (this can take up to 24-48 hours depending on your provider and configuration) then the custom domain should be added successfully. Otherwise, try again later once the changes have propegated.

Enable the Cloudflare proxy
Once you’ve verified your domain, you can enable caching on Cloudflare. Go back to your domain or subdomain in the DNS tab, and click the cloud icon until it’s orange and “Proxied” shows.

Then go to “Caching” and set the “Caching level” to standard.

Finally, by default Cloudflare will only cache certain types of files. If you’re serving predominantly static HTML or CSS files, this might be OK but if you’re sending other content types such as JSON you’ll need to add a page rule so that the files are cached.

Go to the “Page Rules” tab, and choose “Create Page Rule”. Enter the domain/subdomain you’re using for blob storage (eg cdn.example.com) and then click “Add a setting”. Choose “Cache Level” and select “Cache Everything”. This will now cache everything served on this domain, using either the Cloudflare defaults or the cache-control headers applied to the individual files.

Upload files to Blob Storage with cache-control headers set
Now, upload some files to your blob storage account in the Azure Portal. Depending on how you upload the files, you’ll need to set the cache-control headers. The .NET SDK has built-in support, or you can use these instructions to use PowerShell.

Conclusion
By enabling Cloudflare for your domain, you’re now saving money each month on bandwidth costs (Cloudflare will only request resources once the cached copy expires) and protecting yourself from a variety of security attacks.