Cloud services do occasionally fail, e.g. hardware or network failure, bugs, etc. The following URLs provide the current status for a cloud service:
Amazon S3: https://status.aws.amazon.com/
Google Drive: https://www.google.com/appsstatus#hl=en&v=status
Google Storage: https://status.cloud.google.com/
Office 365 and SharePoint: https://status.office365.com/
Amazon Drive (NO LONGER AVAILABLE): https://developer.amazon.com/docs/amazon-drive/ad-status.html
Review our article on Cloud Backup which considers its strengths, its weaknesses, and how Cloud services should form part of your overall backup strategy.