Just for reference, I just updated my two forums, both done within an hour elapsed, in both cases I temporarily resized to 8G RAM and back again. This particular step took about 5mins, with (temporarily) 4 CPUs and 8G RAM.
I, [2024-01-10T16:07:58.323464 #1] INFO -- : > cd /var/www/discourse && su discourse -c 'bundle exec rake themes:update assets:precompile'
110:M 10 Jan 2024 16:08:52.047 * 100 changes in 300 seconds. Saving...
110:M 10 Jan 2024 16:08:52.048 * Background saving started by pid 3276
3276:C 10 Jan 2024 16:08:52.384 * DB saved on disk
3276:C 10 Jan 2024 16:08:52.386 * Fork CoW for RDB: current 1 MB, peak 1 MB, average 0 MB
110:M 10 Jan 2024 16:08:52.449 * Background saving terminated with success
Purging temp files
Bundling assets
MaxMind IP database updates require a license
Please set DISCOURSE_MAXMIND_LICENSE_KEY to one you generated at https://www.maxmind.com
MaxMind IP database updates require a license
Please set DISCOURSE_MAXMIND_LICENSE_KEY to one you generated at https://www.maxmind.com
I, [2024-01-10T16:12:14.362017 #3300] INFO -- : Writing /var/www/discourse/public/assets/break_string-cc617154cd957804f2f6a1f3bc68258c9cdca3d4b9a322bf777d145fed04790e.js
Here we see ember (column 12) is using 2.5G RAM (column 6) and more than one CPU (column 3)
# ps auxfc|egrep -A29 containerd
root 1097 0.2 0.5 1510892 44924 ? Ssl 16:00 0:01 containerd
root 4507 0.1 0.0 717892 7556 ? Sl 16:03 0:00 \_ containerd-shim
root 4530 0.1 0.3 312292 30512 ? Ssl 16:03 0:00 \_ pups
systemd+ 4609 0.0 0.3 213236 28608 ? S 16:03 0:00 \_ postmaster
systemd+ 4617 0.0 0.8 213340 67288 ? Ss 16:03 0:00 | \_ postmaster
systemd+ 4618 0.0 0.0 213236 5876 ? Ss 16:03 0:00 | \_ postmaster
systemd+ 4619 0.0 0.1 213236 10076 ? Ss 16:03 0:00 | \_ postmaster
systemd+ 4620 0.0 0.1 213904 8860 ? Ss 16:03 0:00 | \_ postmaster
systemd+ 4621 0.0 0.0 68004 5592 ? Ss 16:03 0:00 | \_ postmaster
systemd+ 4622 0.0 0.0 213796 7100 ? Ss 16:03 0:00 | \_ postmaster
message+ 4682 0.2 0.4 87976 35724 ? Sl 16:03 0:00 \_ redis-server
1000 7722 1.1 0.0 0 0 ? Z 16:07 0:01 \_ esbuild <defunct>
root 7736 0.0 0.0 2476 520 ? S 16:07 0:00 \_ sh
root 7737 0.0 0.0 9296 4156 ? S 16:07 0:00 | \_ su
1000 7738 8.3 0.0 2476 580 ? Ss 16:07 0:12 | \_ sh
1000 7835 0.4 0.9 929524 78416 ? Sl 16:08 0:00 | \_ node
1000 7857 0.0 0.0 2484 524 ? S 16:08 0:00 | \_ sh
1000 7858 156 30.5 67413228 2491796 ? Sl 16:08 3:37 | \_ ember
1000 7876 39.0 1.7 11486300 145476 ? Ssl 16:08 0:44 | \_ node
1000 7882 36.7 1.5 11466956 122648 ? Ssl 16:08 0:41 | \_ node
1000 7889 37.1 4.1 11647592 340908 ? Ssl 16:08 0:42 | \_ node
1000 7761 1.5 0.0 0 0 ? Z 16:08 0:02 \_ esbuild <defunct>
Probably 4G RAM would have been enough for me, but as noted this whole thing only cost a few cents. (I see now that I could have chosen faster CPUs for an extra cent.)
Edit: I took a backup before I started and another after the job was done, and they were 35 mins apart. So the downtime as seen by the users was no longer than that.
Edit: note that Digital Ocean control panel says the resizing operation may take up to 1min per GB of data on the disk - in my case only 14G and as it turned out only 2 mins for each resize. But if you have a great deal of data on the instance, this resizing dance might take longer. (Then again, if you have a great deal of data you are perhaps not trying to run in less than 4G of RAM)