Using Cloudflare with WWW or a subdomain
If you're using Cloudflare without a subdomain, then you must select ‘Add WWW’ to the domain. This is a limitation that Cloudflare imposes when adding their service through DreamHost. If you wish to use Cloudflare without the www subdomain, you must purchase an account directly through their website.
If your domain is already a subdomain, such as "subdomain.example.com", then there is no need to change the domain hosting options and you can configure Cloudflare on subdomain.example.com.
If your domain uses a content management application like WordPress, this can cause an issue as the URL used by the application has changed. If you need to change your domain to include WWW in the URL, you must make sure to update the URL used in your application or code as well. It’s best to make the changes to your CMS program or code before enabling Cloudflare on the domain.
View the Change WordPress Site URL article for details on how to adjust this setting for a WordPress site.
Using Cloudflare with dreamhosters.com subdomains
Cloudflare cannot be used with dreamhosters.com subdomains at this time.
Using Cloudflare with external nameservers
If your domain is not using DreamHost’s nameservers, you must manually update your domain's DNS records. You can view all of the DNS records that are set up for any site you host at DreamHost simply by clicking the 'DNS' link under the domain name on the (Panel > ‘Domains’ > ‘Manage Domains’) page. View the DNS article for further details.
If the domain uses WWW or the subdomain IP changed, you’ll need to update the IP address at the company that hosts your nameservers. As with any DNS change, the DNS propagation takes several hours to complete.