As was noticed in previous answer, AWS is required for using Bamboo in Cloud. It is however not necessary if you're running Bamboo server.
For server, there are more agent types to choose: local agents (run on the same machine as the server node), remote agents (usually run in the same local network), or elastic agents (on EC2 from AWS) - as an option, not necessity.
As per the below documentations, AWS is a fundamental requirement to use Bamboo Cloud:
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