This just started for me. It looks like they've posted about it on https://status.shopify.com/
Edit: Due to Cloudflare, not Shopify itself https://www.cloudflarestatus.com/
Edit: 45 mins after the first outage my storefront and admin are backup, not sure if everyone's are. Cloudflare claims they've implemented a fix and it seems to be working well. Shopify claims that a majority of the stores affected have now recovered.
Edit: Shopify is now saying that all issues are resolved, thankfully. Cloudflare still is having minor issues but it doesn't seem like they pertain to Shopify's operation.

