Do all your clients use the same stack? Most resellers use 1 big server and cPanel and (although I dislike GUIs and abstractions) I can say that cPanel is reall

Do all your clients use the same stack? Most resellers use 1 big server and cPanel and (although I dislike GUIs and abstractions) I can say that cPanel is really good at what it does. If you're not fond of cPanel and you want to use multiple VPSs you should definitely do it with docker, one container per client and then map them to a CNAME (e.g. www.website.com), you can use AWS, DO or any VPS provider with a mature API to automate the process, use logspout and ELK for logging and you're all set. You can either choose to scale vertically (more servers) or horizontally (increase CPU/RAM).