docs(cluster-management): add hub and spoke feature sets guide

docs/platform/guides/cluster-management/hub-and-spoke-featuresets.md

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+---
+layout: docs
+menu:
+  docsplatform_{{.version}}:
+    identifier: hub-ui-featuresets
+    name: Cluster Types & Feature Sets
+    parent: hub-ui
+    weight: 75
+menu_name: docsplatform_{{.version}}
+section_menu_id: guides
+---
+
+
+# Enable Feature Sets on General, Hub, and Spoke Clusters
+
+A **Feature Set** is a group of product capabilities (for example Backup & Recovery or Databases) that you can enable on a cluster. Where you enable it depends on what kind of cluster you are working with, so first identify the cluster type, then follow the matching steps below.
+
+## Cluster types
+
+Every cluster you add to the platform is one of three types.
+
+| | General cluster | Hub cluster | Spoke cluster |
+|---|---|---|---|
+| What it is | A standalone cluster managed on its own | The central cluster that manages other clusters | A cluster connected to a hub and managed from it |
+| Connected to a hub? | No | It is the hub | Yes |
+| Typical role | Runs workloads; managed individually | Control plane for the fleet; stores cluster state and distributes applications and policies | Runs workloads; receives configuration from the hub |
+| How it is created | Import a cluster without selecting a hub | Enable the **Multicluster Hub** feature set. See [Hub UI](../hub-ui/introduction.md) | Import with a hub selected, or enable **Multicluster Spoke**. See [Create a Spoke Cluster](../hub-ui/spoke.md) |
+| Feature sets are enabled | On that cluster, one cluster at a time | On the hub only | From the hub, per ClusterSet |
+| Scope of one change | That cluster | The hub only | Every spoke in the ClusterSet |
+
+* **ClusterSet**: a named group of spoke clusters. Spoke feature sets are enabled per ClusterSet, not per individual spoke. See [Cluster & Clusterset](../hub-ui/cluster-and-clusterset.md).
+
+## Which cluster type should I use?
+
+Choose the type by how many clusters you manage and whether they should share configuration.
+
+| If your situation is... | Use | Why |
+|---|---|---|
+| One cluster, or a few unrelated clusters you manage separately | **General cluster** | No hub to run or maintain; each cluster is configured on its own |
+| Many clusters that should get the same features and policies | **Hub + spokes** | Configure once on the hub and it applies to every spoke in a ClusterSet |
+| Clusters that need different feature sets (for example production and development) | **Hub + spokes in separate ClusterSets** | Each ClusterSet has its own feature sets |
+
+Trade-off: a hub is an extra cluster to run, and spokes depend on it for feature changes. For a single cluster, a general cluster is simpler.
+
+## Where should I enable the feature on?
+
+This docs refers two wordings : cluster-ui & hub-ui for the cluster views. So, Applying something on hub cluster means accessing ![Cluster-ui](../images/cluster_and_clusterset/cluster-ui.png), But Applying something on hub ui (for its spokes obviously) means accessing ![Hub-ui](../images/cluster_and_clusterset/hub-ui.png). See the switcher, that is the most important thing in this page.
+
+| | General cluster | Hub feature sets | Spoke feature sets |
+|---|---|---|---|
+| Applies to | That cluster only | The hub cluster only | Every spoke in the selected ClusterSet |
+| Where to open it | Cluster → **Overview** → **Feature Sets** | Hub cluster → **Overview** → **Feature Sets** | Hub UI → hub **Overview** → **Cluster Sets** → *ClusterSet* → *feature set* |
+| Example | Enable Databases on a standalone cluster | Enable Backup & Recovery on the hub | Enable Config Syncer on all spokes in `prod-set` |
+
+---
+
+## Enable a feature on the hub cluster
+
+1. Open your hub cluster. The **Overview** page has a **Feature Sets** section.
+2. Select the feature set you want, for example **Backup & Recovery**.
+3. On that feature set's page, enable and configure the features you need.
+
+![Feature Sets grid on the Overview page](../images/cluster-features/features.png)
+
+The full enable flow is the same as for any cluster. See [Manage Feature Sets](../cluster-features.md) and [Cluster Overview](../cluster-overview.md).
+
+---
+
+## Enable a feature on spoke clusters
+
+Spoke feature sets are managed from the hub, per ClusterSet.
+
+1. Open the hub in the Hub UI. The **Overview** page has a **Cluster Sets** section with one card per ClusterSet, showing its name and **Number of Managed Cluster**. Click the ClusterSet that contains your spokes.
+
+   ![Cluster Sets section on the hub Overview page](../images/cluster_and_clusterset/clustersets.png)
+
+2. The ClusterSet's **Feature Sets** page lists every feature set with an **Installed** or **Not Installed** badge. Below the cards, **All cluster overview** and the **Cluster list** show the spokes in this ClusterSet. Click the feature set you want, for example **Secret Management** (**Not Installed**).
+
+   ![Feature Sets page of a ClusterSet](../images/cluster_and_clusterset/cluster_set_feature_1.png)
+
+3. The feature set page lists its **Components**, for example Config Syncer, External Secrets and Reloader. Click **Enable** at the top right.
+
+   ![Secret Management feature set before enabling](../images/cluster_and_clusterset/enable_feature.png)
+
+4. On the **Configure** page, tick the components you want to install. Enabling a component also enables any prerequisite components it needs. Click **Preview**, or **Cancel** to go back without changes.
+
+   ![Select the components to install](../images/cluster_and_clusterset/select_feature.png)
+
+5. **Preview** shows the `helm_release.yaml` that will be applied, in **YAML** or **JSON** with a **Copy** button. Review it, then click **Submit**. Click **Previous** to change your selection.
+
+   ![Preview of the generated helm release](../images/cluster_and_clusterset/preview_feature.png)
+
+6. After a successful submit, the feature set page shows **Configure** and **Disable** in place of **Enable**. Use **Configure** to change the selected components later. Each enabled component is marked with a green check, for example **Config Syncer**.
+
+   ![Feature set after it is enabled](../images/cluster_and_clusterset/enabled_feature.png)
+
+The **Out of sync & Unaligned clusters** table at the bottom of the page lists the spokes in the ClusterSet with two columns:
+
+| Column | Meaning |
+|---|---|
+| **Additional feature list** | Features enabled on the spoke but not on the hub (unaligned) |
+| **Out of sync feature list** | Hub features that have not been applied to the spoke yet |
+
+A `-` in both columns means the spoke matches the hub. **No Data Available** (as before you enable) means there is nothing to compare yet. The change applies to all spoke clusters in the ClusterSet. See [Cluster & Clusterset](../hub-ui/cluster-and-clusterset.md).
+
+> **Note:** Do not manage feature sets directly on a spoke cluster. Make feature changes from the hub so the two stay in sync.
+
+---
+
+## Quick reference
+
+| Task | How to do it |
+|---|---|
+| Enable a feature on a standalone (general) cluster | Cluster → Overview → Feature Sets → *feature set* |
+| Enable a feature on the hub | Hub cluster → Overview → Feature Sets → *feature set* |
+| Enable a feature on all spokes in a group | Hub UI → hub Overview → Cluster Sets → *ClusterSet* → *feature set* → Enable |
+| Check whether spokes match the hub | ClusterSet → *feature set* → Out of sync & Unaligned clusters table |