To avoid missing posts and comments the site will be down, while the upgrade is happening.

EDIT: I will try a new deployment, which should provide zero downtime(blue-green), but if anything goes wrong, there still might be some downtime.

EDIT2: Due to some preparation I had to do for the new deployment rollout, I had to upgrade sooner, than I had mentioned. There was a little downtime, but no comments or posts were lost.