Josef Strzibny writes notes on Ruby, Rails, Elixir, and deploying with Kamal, and promotes his books on deployment and Kamal.
HN links it for practical Kamal deployment guides, such as running multiple apps on one server. The author also describes it as his own notes and book marketing.
I am still writing https://nts.strzibny.name
It's my own retrospection / notes / and now also marketing for my books Deployment from Scratch and Kamal Handbook.
I get around 6k/mo visits, it's not really growing but I also never wrote "for SEO", just whatever I am dealing with.
As for promotion I submit the better posts to Ruby subreddit and I am lucky my posts are often picked up by 2 Ruby newsletters.
You should be able to run multiple services with kamal 2! [0] They'll just be their own config.yml file that you push with the cli.
[0] https://nts.strzibny.name/multiple-apps-single-server-kamal-2/