Here are a few relevant point to upgrading to Debian 9:
Debian 9 (“Stretch”) is still in dev/testing. It’s possible to run into issues in the usage of Debian 9, and it’s possible to run into complications from the upgrade.
That said, most of the changes in a distro release upgrade are to the
apt packages–since you tagged this MineOS Turnkey, I’ll assume that this is how you are using MineOS. I haven’t personally upgraded Turnkey to Stretch, so this is all general speculation.
Here are the packages MineOS Turnkey installs: from normal repos & from third-party repos
Most of these standard packages–if upgraded–will continue to work exactly as they did on Debian 8. From that perspective, you should expect no issues from the upgrade (at least I wouldn’t).
Also, NodeJS is installed through apt, but from a separate repository (configured through that
script line). This will also ensure NodeJS will remain the right version (which is preferably 4.x).
JDK8 is installed from a separate (but official) repo locked into this version. If Stretch makes a newer version available, this will not be downloaded/utilized unless you go through the steps to uninstall it (not necessary, or at least: not necessary until you confirm everything else went well)
To that end, I expect upgrading to be safe. But as always, you should go through preventative measures to protect against upgrade-related issues:
- Stop all your servers beforehand (obvious, right?)
- Make an archive of your servers
- Copy your most recent archive off the server machine (sftp client is always nice from your desktop!)
Last thing to remember: so long as you protect your server archives, you can just as well demolish your server and you’ll always be able to get back to a Turnkey install (or a fresh Debian 9 install). So don’t be afraid of bricking your server–I know when I’ve done it (on things like kernel recompiling in the past), it has always been educational!