Create a domain name for the content delivery through CDN. Note that a CNAME must differ from your origin source.
Add a DNS record in your website administration panel for a CNAME before using it for integration.
cdn.example.ru. CNAME d.gcdn.co
For working with HTTPS your SSL certificate must secure CNAME or be a wildcard. Read more on SSL certificates.
If you do not have access to the DNS records or prefer to work with our shared SSL certificate choose gcdn.co zone CNAME (*.gcdn.co).
A free SSL-certificate is applied for the resource by default.
Note, that the CNAME type can't be changed after a CDN Resource creation.
Check the CNAME record
Run dig command in the console on your computer or use online services.
If the CNAME was added in a right way, you will see the record as follows:
cdn.site.ru 14399 IN CNAME d.gcdn.co
If you see other answers, check your DNS settings or contact your hosting provider support.
As soon as your CNAME is added to DNS panel and provisioned, you can use it to integrate your website with a CDN.