docs: Add snap upgrades how-to (#934)

docs/src/snap/howto/index.md

@@ -23,6 +23,7 @@ backup-restore
 refresh-certs
 restore-quorum
 two-node-ha
+Managing upgrades <upgrades>
 Set up Enhanced Platform Awareness <epa>
 contribute
 Get support <support>

docs/src/snap/howto/upgrades.md

@@ -0,0 +1,108 @@
+# Upgrading the snap
+
+Upgrading the Kubernetes version of a node is a critical operation that 
+requires careful planning and execution. {{product}} is shipped as a snap,
+which simplifies the upgrade process.
+This how-to guide will cover the steps to upgrade the {{product}} snap 
+and how to put a hold on upgrades if desired.
+
+## Important Considerations Before Upgrading
+
+- According to the [upstream Kubernetes][1], skipping **minor** versions while 
+upgrading is not supported. For more details, please visit the
+[Version Skew Policy][2].
+- Before performing an upgrade, it's important to back up the cluster data. 
+This can be done by following the steps outlined in the [backup guide][3].
+- For more information on managing snap updates, please refer to the 
+[snap documentation][4].
+
+## Patch Upgrade
+
+Patch upgrades address bug fixes and are typically safe, introducing no 
+breaking changes.
+Snaps automatically check for updates of their specific track 
+(e.g. `1.32-classic`) several times a day and apply them when available.
+These updates ensure that the latest changes in the installed track are applied.
+Patch upgrades can also be triggered manually by following the steps below.
+
+1. **List available revisions:**
+
+```
+snap info k8s
+```
+
+2. **Refresh the snap:**
+
+```
+snap refresh k8s
+```
+
+3. **Verify the upgrade:**
+
+Ensure that the upgrade was successful by checking the version of the snap and 
+confirming that the cluster is ready:
+
+```
+snap info k8s
+sudo k8s status --wait-ready
+```
+
+## Minor Version Upgrade
+
+Minor versions add new features or deprecate existing features without 
+breaking changes.
+To upgrade to a new minor version, the snap channel needs to be changed.
+
+
+1. **List available channels:**
+
+```
+snap info k8s
+```
+
+2. **Change the snap channel:**
+
+The {{product}} snap channel can be changed by using the `snap refresh` 
+command.
+
+```
+snap refresh --channel=1.33/stable k8s
+```
+
+3. **Verify the upgrade:**
+
+Ensure that the upgrade was successful by checking the version of the snap 
+and confirming that the cluster is ready:
+
+```
+snap info k8s
+sudo k8s status --wait-ready
+```
+
+```{note}
+In a multi-node cluster, the upgrade should be performed on all nodes.
+```
+
+## Freezing Upgrades
+
+To prevent automatic updates, the snap can be tied to a specific revision. 
+`snap refresh --hold[=<duration>]` holds snap refreshes for a specified 
+duration (or forever, if no value is specified).
+
+```
+snap refresh k8s --hold
+```
+
+Or specify a time window:
+
+```
+snap refresh k8s --hold=24h
+```
+
+<!-- LINKS -->
+[1]: https://kubernetes.io/docs/tasks/administer-cluster/kubeadm/kubeadm-upgrade/
+[2]: https://kubernetes.io/docs/setup/release/version-skew-policy/
+[3]: ./backup-restore.md
+[4]: https://snapcraft.io/docs/managing-updates
+[5]: ../../charm/index.md
+[6]: ../../capi/index.md