The site is static, hosted on GitHub Pages and generated via Jekyll, backed by Cloudflare for extra HN-proofing.
As of this comment, there are 150-170 concurrent users on the site, with about 120 of them (~80%) from HN. Although I do have the data, I am hesitant to do a write up since I would need to correlate traffic to the rank of a submission on HN, which I do not have in retrospect. (For example, a post at #1 can get 300 concurrent users while this post at #3 only 150. Posts in #20-30 are lucky to get 50 concurrents. For further reference, note that Reddit posts which hit the front page of a default like /r/dataisbeautiful can get 1,000 concurrents.)
EDIT: When this post dropped to #4, traffic immediately dropped to 100-110 concurrents.