Does anyone have any recommendations for how to recover from a CF update that leaves the server broken in some way? I've always stopped the service and taken a backup of the cfusion directory, which I can restore from if the update goes sideways. However, I've hit a couple of situations lately where restoring that as it was before the update was insufficient, server was still twisted. Do I need to back up and restore the entire ColdFusion2021 directory? Its inconveniently large, and contains some useful stuff I'd rather not lose, logs for instance, and others that aren't coming to mind. Do updates ever do anything outside cfusion? For that matter, anything outside ColdFusion2021? Other ideas?

Read the logs to determine what is causing the outage is a starting point.

Hey Dave - Yes, CF updates only update files inside the ColdFusion2021 directory. Every update takes it's own backup of files it's going to replace before it begins. If you look inside the cfusion/hf-updates directory you'll see your downloaded hf directories (something like hf-2021-00012-xxxxxx) and their corresponding properties file. Inside those directories are the "backup" directories. Those are the original files before the HF took effect. To roll back, first I'd stop all the CF services (add-ons too) and run the uninstall.jar in the cfusion/hf-updates/hf-2021-00012-xxxxxx/uninstall directory. That's usually all you need to do. If the uninstall fails and you need to manually restore, stop the CF services (and any add-ons), copy the contents of the cfusion/hf-updates/hf-2021-00012-xxxxxx/backup directory and paste it right over everything in the cfusion directory. Then, delete the whole cfusion/hf-updates/hf-T2021-00012-xxxxxx directory and associated properties file. Start the CF services and you're back to where you were.

Thank you @David Belanger. So it doesn't modify anything outside the ColdFusion2021, but it DOES modify things outside cfusion, right?

That's correct. Before 2021, there was only the built-in java and the Tomcat configuration files outside of cfusion. Adobe only updates the built-in java on new major releases. As of 2021, the modules folder was added outside the cfusion as well. That being said, sometimes when you install an HF update you'll restart CF and see that some of the modules now need an update. But in your case, if your HF update failed, I doubt you would have updated any modules. If you had updated any modules, you may have to roll them back manually too (but that's pretty easy using the GUI or the CLI tool)

I usually have to reinstall the SAML module after the updates. For whatever reason, it complains that some files are not found. Uninstall then reinstall fix it.