docs: add how-to section on making upgrades

docs/howto/admin/upgrade-tljh.md

@@ -0,0 +1,64 @@
+(howto-admin-upgrade-tljh)=
+
+# Upgrade TLJH
+
+An TLJH installation is supposed to be upgradable to get updates to JupyterHub
+itself and its dependencies in the [hub environment](hub-environment). For
+details on what is done during an upgrade, see
+[](topic-installer-upgrade-actions).
+
+## Step 1: Read the changelog
+
+Before making an upgrade, please read the [](changelog) to become aware about
+breaking changes. If there are breaking changes, you may need to update your
+configuration files or take other actions as well as part of the upgrade.
+
+Adjusting to the breaking changes isn't part of this documentation, please rely
+on the TLJH changelog and the changelogs of related projects linked to from the
+TLJH changelog.
+
+## Step 2: Consider making a backup
+
+Before making an upgrade, consider if you want to first make a backup in some
+way. While upgrades between TLJH versions are tested with automation, there are
+no guarantees.
+
+This project does't yet provide documentation on how to make backups, but if
+TLJH is installed on a virtual machine in a cloud, a good option is to try
+create a snapshot of the associated disk. If this isn't an option, you could
+consider making a backup of the files in `/opt/tljh` that contain most but not
+all things during an upgrade, or perhaps only the JupyterHub database with
+information about its users in `/opt/tljh/state` together with some other
+details.
+
+## Step 3: Make the upgrade
+
+To initialize the upgrade, do the following from a terminal on the machine where
+TLJH is installed.
+
+```shell
+# IMPORTANT: This should NOT be run from a JupyterHub started user server, but
+#            should only run from a standalone terminal session in the machine
+#            where TLJH has been installed.
+#
+curl -L https://tljh.jupyter.org/bootstrap.py \
+  | sudo python3 - \
+    --version=latest
+```
+
+You can also upgrade to specific version by changing `--version=latest` to
+`--version=1.0.0` or similar. There is no need to specify admin users etc again.
+
+## Step 4: Verify function
+
+After having made an upgrade its always good to verify that the JupyterHub
+installation still works as expected. You may want to try logging out, logging
+in, and starting a new server for example.
+
+If you have issues consider the [](troubleshooting) documentation. If you need
+help you can ask questions in [Jupyter forum], and if you think there is a bug
+or documentation improvement that should be made you can open an issue or pull
+request in the [TLJH GitHub project].
+
+[jupyter forum]: https://discourse.jupyter.org/c/jupyterhub/tljh
+[tljh github project]: https://github.com/jupyterhub/the-littlest-jupyterhub

docs/howto/index.md

@@ -56,6 +56,7 @@ admin/nbresuse
 admin/https
 admin/enable-extensions
 admin/systemd
+admin/upgrade-tljh
 ```
 
 ## Cloud provider configuration

docs/troubleshooting/index.md

@@ -1,3 +1,5 @@
+(troubleshooting)=
+
 # Troubleshooting
 
 In time, all systems have issues that need to be debugged. Troubleshooting