From Facebook a breakdown of several hours may have ended, and apparently, it's Apple's turn to suffer a system crash. The company is report recurring issues on almost all iCloud services from 11am ET today.
Apple gives no details about the problems, only that "some users are affected" and that "users may not be able to access this service". However, according to the support page of the company, the problem is widespread. iCloud connection, backup, calendar, contacts, messaging, keychain, iCloud Drive file storage, iWork, photos, notes, reminders, find my iPhone, etc., are apparently affected by the problem.
The iCloud failure marks the third major technical failure in as many days, after Gmail and Google Drive issues earlier in the week and yesterday Facebook, WhatsApp and Instagram failures due to a change in the server configuration. It's unclear when iCloud services will return to normal, but Apple System Status Page is probably your best choice for tracking issues.