It states that Apple uses Amazon Web Services and Google Cloud Platform for iCloud services. Details are as below.
Apple updated the page that showed the security outline of its cloud service “iCloud” on April 4, 2019 local time, and some data of iCloud to servers of third-party partners such as Amazon Web Services and Google Cloud Platform It states clearly that it has been saved.
In some cases, your iCloud data may be stored using third-party partners—such as Amazon Web Services or Google Cloud Platform—but these partners don’t have the keys to decrypt your data stored on their servers.
iCloud security overview-Apple Support
iCloud and Third Party Services
iCloud service data is published by Apple on a regular white paper ” iOS Security Guid “ that AWS and Microsoft Azure use AWS and GCP from 2017 to 2016 from 2011 to 2016 Although it was clearly stated, in the latest iOS Security iOS 12.1 November 2018, it was clearly stated as “Apple and third-party storage services.”, And it was unclear which service was being used,
The updated iCloud security overview states that iCloud data is stored on third party server partners (AWS and GCP), but the partner has no key to decrypt the user data stored on the server As a result, the dependence on Amazon and Google does not seem to change.
In addition, iCloud security overview adds that the screen time introduced in iOS 12 as with Keychain and Message in iCloud, and the vocabulary learned with Quicktype Keyboard are subject to end-to-end encryption.