docs: High availability explanation page (#940)

docs/src/snap/explanation/high-availability.md

@@ -0,0 +1,44 @@
+# High availability
+
+High availability (HA) is a core feature of {{ product }}, ensuring that
+a Kubernetes cluster remains operational and resilient, even when nodes or
+critical components encounter failures. This capability is crucial for
+maintaining continuous service for applications and workloads running in
+production environments.
+
+HA is automatically enabled in {{ product }} for clusters with three or
+more nodes independent of the deployment method. By distributing key components
+across multiple nodes, HA reduces the risk of downtime and service
+interruptions, offering built-in redundancy and fault tolerance.
+
+## Key components of a highly available cluster
+
+A highly available Kubernetes cluster exhibits the following characteristics:
+
+### 1. **Multiple nodes for redundancy**
+
+Having multiple nodes in the cluster ensures workload distribution and
+redundancy. If one node fails, workloads will be rescheduled automatically on
+other available nodes without disrupting services. This node-level redundancy
+minimizes the impact of hardware or network failures.
+
+### 2. **Control plane redundancy**
+
+The control plane manages the cluster’s state and operations. For high
+availability, the control plane components—such as the API server, scheduler,
+and controller-manager—are distributed across multiple nodes. This prevents a
+single point of failure from rendering the cluster inoperable.
+
+### 3. **Highly available datastore**
+
+By default, {{ product }} uses **dqlite** to manage the Kubernetes
+cluster state. Dqlite leverages the Raft consensus algorithm for leader
+election and voting, ensuring reliable data replication and failover
+capabilities. When a leader node fails, a new leader is elected seamlessly
+without administrative intervention. This mechanism allows the cluster to
+remain operational even in the event of node failures. More details on
+replication and leader elections can be found in
+the [dqlite replication documentation][Dqlite-replication].
+
+<!-- LINKS -->
+[Dqlite-replication]: https://dqlite.io/docs/explanation/replication

docs/src/snap/explanation/index.md

@@ -18,6 +18,7 @@ channels
 clustering
 ingress
 epa
+high-availability
 security
 cis
 ```