Hello!
I like many here in the forum, when updating Ghost to version 4 I had an error on my site, which threw a 502/503 error or possibly also launched the message “We’ll be right back”.
Well, after spending a couple of hours trying to fix it, I finally came up with a solution that worked for me and I share it with you, to see if it works anyway for you.
It should be noted that I am using Ubuntu with DigitalOcean, but don’t be alarmed, just try to adapt the steps to the distribution or place where you have Ghost installed.
Note: If you are using DigitalOcean, I recommend you follow the steps with the ghost-mgr user. In the event that you do not have this user, just be careful with the permissions, especially if you are with root.
1. Remove Ghost-CLI
The first thing I did was remove the Ghost-CLI, using npm.
$ npm uninstall ghost-cli --global
Make sure you no longer have it, run any
ghostcommand and get an error as a result.
2. Uninstall node
The following is to do the same, but with nodejs.
If you are using nvm
nvm already brings problems to Ghost by installing it locally in / root or / home, so it would be best not to use it and choose to install node in the usual way.
Make sure you know the current breadcrumb of Node first, then remove it.
$ nvm which 14.0 # Just make sure you use the version you have
Later we proceed to uninstall:
$ rm -rf $NVM_DIR ~/.npm ~/.bower
$ unset NVM_DIR;
$ which node;
$ rm -rf {path_to_node_version} # The route that we previously took
Open ~/.bash_profile or ~/.bashrc and remove any nvm lines.
If you are using node without nvm
For the second case, node would have to be removed from the system. In my case, I installed it with apt-get, so I removed it in the same way.
$ sudo apt-get remove nodejs
To remove both the package and the configuration files run:
$ sudo apt-get purge nodejs
As a final step, you can run the command below to remove any unused files and free up the disk space
$ sudo apt-get autoremove
3.Install node & npm
Well, now we are going to reinstall Nodejs, in the traditional way and without nvm. In my case, that I am with Ubuntu, I will use apt-get.
To start off, add the NodeJS PPA to your system using the following commands.
$ sudo apt-get install software-properties-common
Next, add the NodeJS PPA.
Version v12.21.0 worked for me, I have also seen that version 12.x is recommended for this problem. So I also recommend doing the same.
$ curl -sL https://deb.nodesource.com/setup_12.x | sudo -E bash -
It’s time now to install NodeJS using the command below.
$ sudo apt-get install nodejs
Verify that everything is working correctly.
$ node -v
4. Reinstall Ghost-CLI
$ sudo npm install -g ghost-cli@latest
5. Update Ghost again
Finally update Ghost again to version 4 (/var/www/ghost).
$ ghost update --force
And finally run start
$ ghost start
Bonus
As a bonus, another common problem that I have seen related to the same issue is the systemd. For this I leave you the following article that can help with that problem.
Well, I hope this has solved the problem for you, it worked for me and I would like it to be so with you.
Greetings 
!
