Proposal: YurtCluster Operator for converting K8S to OpenYurt (#389)

Signed-off-by: nunu <[email protected]>

20210722-yurtcluster-operator.md

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+---
+title: YurtCluster Operator
+authors:
+  - "@gnunu"
+  - "@lindayu17"
+reviewers:
+  - "@rambohe-ch"
+  - "@guofei"
+  - "@kadisi"
+  - "@wenjun93"
+creation-date: 2021-07-22
+last-updated: 2021-07-22
+status: provisional
+---
+
+# Convert Vanilla Kubernetes cluster to OpenYurt cluster through Operator
+
+## Table of Contents
+* [Convert Vanilla Kubernetes cluster to OpenYurt cluster through Opertaor](#convert-vanilla-kubernetes-cluster-to-openyurt-cluster-through-operator)
+  * [Table of Contents](#table-of-contents)
+  * [Glossary](#glossary)
+  * [Summary](#summary)
+  * [Motivation](#motivation)
+    * [Goals](#goals)
+    * [Non-Goals/Future Work](#non-goalsfuture-work)
+  * [Proposal](#proposal)
+    * [User Stories](#user-stories)
+      * [Story 1](#story-1)
+      * [Story 2](#story-2)
+    * [Requirements](#requirements)
+      * [Functional Requirements](#functional-requirements)
+        * [FR1](#fr1)
+        * [FR2](#fr2)
+        * [FR3](#fr3)
+        * [FR4](#fr4)
+      * [Non-Functional Requirements](#non-functional-requirements)
+        * [NFR1](#nfr1)
+        * [NFR2](#nfr2)
+      * [Implementation Details/Notes/Constraints](#implementation-detailsnotesconstraints)
+      * [Risks and Mitigations](#risks-and-mitigations)
+  * [Alternatives](#alternatives)
+  * [Upgrade Strategy](#upgrade-strategy)
+  * [Additional Details](#additional-details)
+    * [Test Plan](#test-plan)
+  * [Implementation History](#implementation-history)
+
+## Glossary
+
+Refer to the [Cluster API Book Glossary](https://cluster-api.sigs.k8s.io/reference/glossary.html).
+
+## Summary
+
+This YurtCluster Operator is to translate a vanilla Kubernetes cluster into an OpenYurt cluster, through a simple API (YurtCluster CRD).
+
+## Motivation
+
+To make OpenYurt translation easy for user, i.e., as automative as possible.
+
+### Goals
+* Convert nodes automatically
+* Revert nodes automatically
+* Translated OpenYurt cluster should be the same as through yurtctl or doing manually
+
+### Non-Goals/Future Work
+
+This is NOT a replacement of yurtctl command.
+
+## Proposal
+
+This is an operator, with CRD and Controller.
+
+CRD's definition:
+
+```go
+type ComponentConfig struct {
+        Enabled bool   `json:"enebled,omitempty"`
+        Version string `json:"version,omitempty"`
+}
+
+type NodeSpec struct {
+        Names           []string `json:"names,omitempty"`
+        Pattern         string   `json:"pattern,omitempty"`
+        ExcludedNames   []string `json:"excludedNames,omitempty"`
+        ExcludedPattern string   `json:"excludedPattern,omitempty"`
+}
+
+type FailedNode struct {
+        Name string `json:"name,omitempty"`
+        Info string `json:"info,omitempty"`
+}
+
+// YurtClusterSpec defines the desired state of YurtCluster
+type YurtClusterSpec struct {
+        CloudNodes            NodeSpec        `json:"cloudNodes,omitempty"`
+        EdgeNodes             NodeSpec        `json:"edgeNodes,omitempty"`
+        YurtHub               ComponentConfig `json:"yurtHub,omitempty"`
+        YurtControllerManager ComponentConfig `json:"yurtControllerManager,omitempty"`
+        TunnelService         ComponentConfig `json:"yurtTunnel,omitempty"`
+        AppManager            ComponentConfig `json:"appManger,omitempty"`
+}
+
+// YurtClusterStatus defines the observed state of YurtCluster
+type YurtClusterStatus struct {
+        ConvertedCloudNodes   []string        `json:"convertedCloudNodes,omitempty"`
+        ConvertedEdgeNodes    []string        `json:"convertedEdgeNodes,omitempty"`
+        YurtHub               ComponentConfig `json:"yurtHub,omitempty"`
+        YurtControllerManager ComponentConfig `json:"yurtControllerManager,omitempty"`
+        YurtTunnel            ComponentConfig `json:"yurtTunnel,omitempty"`
+        AppManager            ComponentConfig `json:"appManger,omitempty"`
+        ExcludedNodes         []string        `json:"excludedNodes,omitempty"`
+        FailedNodes           []FailedNode    `json:"failedNodes,omitempty"`
+}
+```
+
+The CRD would be enforced to have a cluster singleton CR semantics, through patched name validation for CRD definition. (for kubebuilder, under config/crd/patches)
+
+The controller would listen incomming CR, and analyze the requirements to figure out user's intention, that is, what nodes to convert, and what nodes to revert.
+
+The controller would update status to record converted, reverted, and failed nodes.
+
+The plan:
+This feature would be merged into release 0.7, hopefully.
+
+### User Stories
+
+#### Story 1
+To convert all nodes, including the future added nodes, automatically.
+
+#### Story 2
+To revert some nodes back to normal K8S node.
+
+### Requirements
+
+User should have a Kubernetes cluster setup.
+
+#### Functional Requirements
+
+The Operator would do these things:
+1) Analyze requests
+2) Do nodes conversion
+3) Do nodes reversion
+4) Act on CR deletion
+
+##### FR1
+Analyze requests:
+Through the YurtCluster CR, the controller would figure out what nodes to convert, what nodes to revert, and if enabling addons like YurtTunel and AppManger.
+Th nodes to be converted or reverted can be specified using Regular expressions, the controller would process the nodes set, including those coming in the future.
+
+##### FR2
+Convert:
+From the analysis, the controller would know which nodes should be converted and do conversion automatically.
+
+##### FR3
+Revert:
+From the analysis, the controller would know which nodes should be reverted and do reversion automatically.
+
+##### FR4
+On CR deletion, the controller should undo anything done to the original K8S cluster, that is, recover back to the origin point.
+
+#### Non-Functional Requirements
+
+##### NFR1
+This operator should not cause any performance impact to the cluster.
+
+##### NFR2
+This operator should keep cluster serects safe.
+
+### Implementation Details/Notes/Constraints
+
+The procedure of coverting/reverting a node will refer to yurtctl's implementation.
+
+Wheteher or not use helm is to be discovered.
+
+### Risks and Mitigations
+
+If number of nodes is large, the performance may be a concern.
+Solution: reduce non-necessary actions as low as possible, and keep necessary cache to reduce api-server/etcd access.
+
+## Alternatives
+
+yurtctl: the classic command to do the cluster conversion/reversion.
+manual: user should convert/revert nodes manually.
+
+## Upgrade Strategy
+
+The Operator supports OpenYurt components upgrade, such as YuntTunnel and AppManager.
+
+For Operator itself, upgrade would have no side effects, idempotent semantics would be kept.
+
+## Additional Details
+
+### Test Plan
+
+test minikube
+test kind
+test kubeadm
+test Operator upgrade
+
+## Implementation History
+
+[x] 03/27/2021: Proposed idea in an issue (https://github.com/openyurtio/openyurt/issues/328).