Are devices on Amazon Web Services device farm real?
I was just curious that where those devices are placed and how can they work simultaneously for thousands of users?
Some of this is covered in the Device Farm FAQ, e.g.
Q: Does AWS Device Farm use simulators or emulators?
AWS Device Farm tests are run on real, non-rooted devices. The devices are a mixture of OEM and carrier-branded devices.
Q: How do you clean up devices after my testing is completed?
After test execution completes, we perform a series of cleanup tasks on each device, including uninstallation of your app. If we cannot verify uninstallation of your app or any of the other cleanup steps, the device will be removed and will no longer be available.
While we continue to add additional cleanup steps and improve the cleanup process, it is possible for data to persist between sessions in some cases, especially if you make use of the device system outside the context of your app. For this reason, and because AWS Device Farm captures video and logs of activity taking place during your use of each device, it is recommended that you avoid providing or entering sensitive information such as account info (E.g., Google Account, Apple ID), personal information, and other security-sensitive details during your automated test and remote access sessions.
I recommend visiting that page and reading the entire FAQ.
The actual mechanics of how Amazon provisions Device Farm devices probably aren't available publicly.