On October 21st there was a large scale Denial-of-Service attack directed against Dyn DNS. While Cloudflare services were operating normally, if you were using both Cloudflare and Dyn services, your website may have been affected.
Specifically, if you are using CNAME records which point to a zone hosted on Dyn, our DNS queries directed to Dyn might fail making your website unavailable, and presenting a “1001” error message.
As a possible workaround, you might be able to update your Cloudflare DNS records from CNAMEs (referring to Dyn hosted records) to A/AAAA records specifying the origin IP of your website. This will allow Cloudflare to reach your origin without the need for an external DNS lookup.
Note that if you use different origin IP addresses (for example based on the geographical location) you may lose some of that functionality by using plain A/AAAA records. We recommend that you provide addresses for many of your different locations, so that load will be shared amongst them.
Customers with a CNAME setup (which means Cloudflare is not configured in your domain NS records) where the main zone is hosted on a Dyn service will be affected as well. You might be able to make Cloudflare your authoritative DNS provider by contacting support and asking to be changed to Full mode and then updating your nameservers at your registrar, but the change can take up to 24h to propagate.
Please note that the Cloudflare status page and support system might be affected by the ongoing attack, since they are hosted on third parties, as per industry best practices.