Merge pull request 2i2c-org#3511 from GeorgianaElena/upgrade-policy

Add a short initial policy about k8s version used in our clusters

docs/howto/upgrade-cluster/index.md

@@ -5,14 +5,26 @@ How we upgrade a Kubernetes cluster is specific to the cloud provider. This
 section covers topics in upgrading an existing Kubernetes cluster.
 
 ```{warning}
-As of now, we have not yet established practices on when to upgrade our
-Kubernetes clusters. Establishing this is tracked in [this GitHub
-issue](https://github.com/2i2c-org/infrastructure/issues/412).
-
 As of now, we also only have written documentation for how to upgrade Kubernetes
 clusters on AWS.
 ```
 
+## Upgrade policy
+
+We aim to ensure we use a k8s version for the control plane and node groups that is at least **five minor versions** behind the latest one available at any given time.
+
+Ideally, the following rules should also be respected:
+
+1. Every new cluster we deploy should be using the latest available kubernetes version.
+1. All of the clusters deployed in a cloud provider should be using the same version.
+1. Check if new upgrades are needed at least every 3 months.
+
+
+```{warning}
+As of now, we have not yet established practices on how to ensure these upgrades happen according to the policy above. Establishing this is tracked in [this GitHub
+issue](https://github.com/2i2c-org/infrastructure/issues/412).
+```
+
 ```{toctree}
 :maxdepth: 1
 :caption: Upgrading Kubernetes clusters