Amazon told Signal not to use its AWS servers for domain-fronting, a technique used to enable communications in countries such as Egypt, Oman, Qatar and UAE. The move was admonished by anti-censorship and free speech advocates at the American Civil Liberties Union and the Electronic Frontier Foundation. Amazon follows a similar move by Google earlier this year also threatened to push Signal off its platform if it continued to use the technique on its servers. The technique uses HTTPS to communicate with a censored host while appearing, on the outside, to be communicating with a different, permitted host.
Source: https://threatpost.com/free-speech-advocates-blast-amazon-over-threats-against-signal/131640/