I was frustrated by CW's lack of being able to process book covers, where each cover listed showed a "Cover Not Available".
The dev who wrote Calibre-Web is keeping it in maintenance mode for the foreseeable future, so a nice dev in Germany forked the project and made it much simpler to deploy in Docker, on your own server or a VPS.
You can find it on GitHub here:
https://github.com/crocodilestick/Calibre-Web-Automator