Anything that can go wrong will go wrong
Long story. I decided to upgrade my server OS. Everything, almost everything, went fine. But, when I try to access my website, I couldn't. I just update some nginx settings and reload the configuration file, and it worked. Nothing fancy, quite easy, actually.
I visited my web site and tried to reach my blog, but I couldn't. I thought, I just forgot to restart forever. Then, I did but nothing happened. I started Ghost manually and saw the problem. Node were upgraded and my old Ghost blog didn't support this new version.
I should check Ghost/nodeJS version compatibility but I didn't. Actually, I should have a Dockerised environment of my droplet. By doing so, I would have known what could happen if I upgrade my server operating system. A zero-cost environment could saved me a lot of time and stress. Huge mistake.
Crying over the spilled milk never is a good choice. My choices were, either downgrade nodeJS and keep my old Ghost version or upgrade Ghost. I chose the latter. I installed the Ghost client, MySQL and the latest Ghost version. Nice and easy, at first, though. I tried to import my old blog post into my new Ghost, but I couldn't. Another issue came out. Ghost asked me for a JSON backup and I haven't done that before. I thought a database backup was enough, but it wasn't. Another mistake to my bag.