Merge pull request #46982 from Jefftree/cle

[KEP-4355] Coordinated Leader Election alpha documentation

Author: k8s-ci-robot

content/en/docs/concepts/cluster-administration/coordinated-leader-election.md

@@ -0,0 +1,40 @@
+---
+reviewers:
+- jpbetz
+title: Coordinated Leader Election
+content_type: concept
+weight: 200
+---
+
+<!-- overview -->
+
+{{< feature-state feature_gate_name="CoordinatedLeaderElection" >}}
+
+Kubernetes {{< skew currentVersion >}} includes an alpha feature that allows {{<
+glossary_tooltip text="control plane" term_id="control-plane" >}} components to
+deterministically select a leader via _coordinated leader election_.
+This is useful to satisfy Kubernetes version skew constraints during cluster upgrades.
+Currently, the only builtin selection strategy is `OldestEmulationVersion`,
+preferring the leader with the lowest emulation version, followed by binary
+version, followed by creation timestamp.
+
+## Enabling coordinated leader election
+
+Ensure that `CoordinatedLeaderElection` [feature
+gate](/docs/reference/command-line-tools-reference/feature-gates/) is enabled
+when you start the {{< glossary_tooltip text="API Server"
+term_id="kube-apiserver" >}}: and that the `coordination.k8s.io/v1alpha1` API group is
+enabled.
+
+This can be done by setting flags `--feature-gates="CoordinatedLeaderElection=true"` and
+`--runtime-config="coordination.k8s.io/v1alpha1=true"`.
+
+## Component configuration
+Provided that you have enabled the `CoordinatedLeaderElection` feature gate _and_  
+have the `coordination.k8s.io/v1alpha1` API group enabled, compatible control plane  
+components automatically use the LeaseCandidate and Lease APIs to elect a leader  
+as needed.  
+
+For Kubernetes {{< skew currentVersion >}}, two control plane components  
+(kube-controller-manager and kube-scheduler) automatically use coordinated  
+leader election when the feature gate and API group are enabled.  

content/en/docs/reference/command-line-tools-reference/feature-gates/coordinated-leader-election.md

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+---
+title: CoordinatedLeaderElection
+content_type: feature_gate
+_build:
+  list: never
+  render: false
+
+stages:
+  - stage: alpha
+    defaultValue: false
+    fromVersion: "1.31"
+---
+Enables the behaviors supporting the LeaseCandidate API, and also enables
+coordinated leader election for the Kubernetes control plane, deterministically.

content/en/docs/reference/kubernetes-api/cluster-resources/lease-candidate-v1alpha1.md

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+---
+api_metadata:
+  apiVersion: "coordination.k8s.io/v1alpha1"
+  import: "k8s.io/api/coordination/v1alpha1"
+  kind: "LeaseCandidate"
+content_type: "api_reference"
+description: "This is a placeholder page to be overwritten when the docs are generated for 1.31"
+title: "LeaseCandidate"
+weight: 5
+---
+
+