Amazon doesn't really have a "primary e-commerce front-end stack" in any concrete sense. They have hundreds/thousands of teams that deploy bits and pieces to a massive pipeline that ultimately makes up what you see on Amazon.com, but each team can have their own infrastructure backing things. Some teams might run everything off a dozen low-end EC2 instances while another sibling team has 3k+ instances; it's really all over the place, and that's ignoring specific events like Black Friday or Prime Day, etc. where teams need to prescale things in advance.

Source: Worked at Amazon/AWS for almost a decade.