First of all, I would like to thank the Lemmy.world team and the 2 admins of other servers @stanford@discuss.as200950.com and @sunaurus@lemm.ee for their help! We did some thorough troubleshooting to get this working!
The upgrade
The upgrade itself isn't too hard. Create a backup, and then change the image names in the docker-compose.yml and restart.
But, like the first 2 tries, after a few minutes the site started getting slow until it stopped responding. Then the troubleshooting started.
The solutions
What I had noticed previously, is that the lemmy container could reach around 1500% CPU usage, above that the site got slow. Which is weird, because the server has 64 threads, so 6400% should be the max.
So we tried what @sunaurus@lemm.ee had suggested before: we created extra lemmy containers to spread the load. (And extra lemmy-ui containers). And used nginx to load balance between them.
Et voilΓ . That seems to work.
Also, as suggested by him, we start the lemmy containers with the scheduler disabled, and have 1 extra lemmy running with the scheduler enabled, unused for other stuff.
There will be room for improvement, and probably new bugs, but we're very happy lemmy.world is now at 0.18.1-rc. This fixes a lot of bugs.
I'm one of the many who have had trouble logging in, and this issue is surely underreported as those affected generally aren't able to report it. It also seems like I'm not able to upvote or downvote. I'll update with any more issues that I come across but I only just now became able to log-in after a long wait and several different browsers.
Edit: it seems like I can successfully upvote/downvote, but the updated vote count and my blue/red arrow only show after refreshing the page. Thanks for all the work you put into this instance btw