add general docs for leases

Signed-off-by: Andrew Sy Kim <andrewsy@google.com>

content/en/docs/concepts/architecture/leases.md

@@ -0,0 +1,40 @@
+---
+title: Leases
+content_type: concept
+weight: 30
+---
+
+<!-- overview -->
+
+Distrbuted systems often have a need for "leases", which provides a mechanism to lock shared resources and coordinate activity between nodes.
+In Kubernetes, the "lease" concept is represented by `Lease` objects in the `coordination.k8s.io` API group, which are used for system-critical
+capabilities like node heart beats and component-level leader election.
+
+<!-- body -->
+
+## Node Heart Beats
+
+Kubernetes uses the Lease API to communicate kubelet node heart beats to the Kubernetes API server.
+For every `Node` , there is a `Lease` object with a matching name in the `kube-node-lease`
+namespace. Under the hood, every kubelet heart beat is an UPDATE request to this `Lease` object, updating
+the `spec.renewTime` field for the Lease. The Kubernetes control plane uses the time stamp of this field
+to determine the availability of this `Node`.
+
+See [Node Lease objects](/docs/concepts/architecture/nodes/#heartbeats) for more details.
+
+## Leader Election
+
+Leases are also used in Kubernetes to ensure only one instance of a component is running at any given time.
+This is used by control plane components like `kube-controller-manager` and `kube-scheduler` in
+HA configurations, where only one instance of the component should be actively running while the other
+instances are on stand-by.
+
+## kube-apiserver identity
+
+{{< feature-state for_k8s_version="v1.26" state="beta" >}}
+
+Starting in Kubernetes v1.26, each `kube-apiserver` uses the Lease API to publish its identity to the
+rest of the system. While not particularly useful on its own, this provides a mechanism for clients to
+discover how many instances of `kube-apiserver` are operating the Kubernetes control plane.
+Existence of kube-apiserver leases enables future capabilities that may require coordination between
+each kube-apiserver.