My secondary DNS server was running on a Pi 3B+, however I really found doing a docker pull was taking a while to download and extract due to the limited hardware specs. In some cases I was seeing 10+ minute extract times… I decided to take advantage of another refurbished PC to replace the Pi, and managed an HP EliteDesk 800 G2 mini desktop for under $200 shipped with the below specs:
Intel Core i5 6400T
16GB DDR4 RAM
256GB SATA SSD
It’s cool, it’s quiet, it’s compact, and it’s got a load of RAM for whatever it ends up getting used for other than secondary DNS. For the time being I’ve put Proxmox on it and had my secondary DNS server setup in with Docker in about half an hour. I may consider trying out Frigate on this with Intel GPU acceleration, and I will likely also use this node for a lot of dev stuff I want to try out rather than doing it on the main host.