Rebuild from the command line takes less ram.
With a two container install, you can build a new container while the old one continues to work (if you have enough ram). That gives you little downtime.
You have to do a command line rebuild sometimes because underlying libraries need to be updated and those can’t be done from the ux.
You can
cd /var/discourse
grep swap discourse-setup
to see the commands that it does to create the swap. If you run swapoff (so that the file is no longer busy) you can then run the commands that create the file (fsallocate) making it bigger, if desired, and format it as swap (mkswap) and then swapon -a to turn it back on.
If you’ve got many plugins you likely need a total of 5 or 6gb.