· cloud
快速实现一个Kubernetes Operator
Kubernetes 提供了众多的扩展功能，比如 CRD、CRI、CSI 等等，强大的扩展功能让 k8s 迅速占领市场。Operator模式可以实现 CRD 并管理自定义资源的生命周期，本文基于kubebuilder快速实现一个 Operator，示例源码见mygame。
Kubebuilder
kubebuilder是一个官方提供快速实现 Operator 的工具包，可快速生成 k8s 的 CRD、Controller、Webhook，用户只需要实现业务逻辑。
类似工具还有operader-sdk，目前正在与
Kubebuilder融合
kubebuilder 封装了controller-runtime与controller-tools，通过controller-gen来生产代码，简化了用户创建 Operator 的步骤。
一般创建 Operator 流程如下：
- 创建工作目录，初始化项目
- 创建 API，填充字段
- 创建 Controller，编写核心协调逻辑(Reconcile)
- 创建 Webhook，实现接口，可选
- 验证测试
- 发布到集群中
示例
我们准备创建一个 2048 的游戏，对外可以提供服务，也能方便地扩缩容。
准备环境
首先你需要有 Kubernetes、Docker、Golang 相关环境。 Linux 下安装 kubebuilder
curl -L -o kubebuilder https://go.kubebuilder.io/dl/latest/$(go env GOOS)/$(go env GOARCH)
chmod +x kubebuilder && mv kubebuilder /usr/local/bin/
创建项目
mkdir -p ~/work/mygame && cd $_
kubebuilder init --domain qingwave.github.io --repo qingwave.github.io/mygame
创建 API
kubebuilder create api --group myapp --version v1 --kind Game
Create Resource [y/n]
y #生成CR
Create Controller [y/n]
y #生成Controller
目录结构如下：
├── api
│ └── v1 # CRD定义
├── bin
│ └── controller-gen
├── config
│ ├── crd # crd配置
│ ├── default
│ ├── manager # operator部署文件
│ ├── prometheus
│ ├── rbac
│ └── samples # cr示例
├── controllers
│ ├── game_controller.go # controller逻辑
│ └── suite_test.go
├── Dockerfile
├── go.mod
├── go.sum
├── hack
│ └── boilerplate.go.txt # 头文件模板
├── main.go # 项目主函数
├── Makefile
└── PROJECT #项目元数据
编写 API
在mygame/api/v1/game_types.go定义我们需要的字段
Spec配置如下
type GameSpec struct {
// Number of desired pods. This is a pointer to distinguish between explicit
// zero and not specified. Defaults to 1.
// +optional
//+kubebuilder:default:=1
//+kubebuilder:validation:Minimum:=1
Replicas *int32 `json:"replicas,omitempty" protobuf:"varint,1,opt,name=replicas"`
// Docker image name
// +optional
Image string `json:"image,omitempty"`
// Ingress Host name
Host string `json:"host,omitempty"`
}
kubebuilder:default可以设置默认值
Status定义如下
const (
Running = "Running"
Pending = "Pending"
NotReady = "NotReady"
Failed = "Failed"
)
type GameStatus struct {
// Phase is the phase of guestbook
Phase string `json:"phase,omitempty"`
// replicas is the number of Pods created by the StatefulSet controller.
Replicas int32 `json:"replicas"`
// readyReplicas is the number of Pods created by the StatefulSet controller that have a Ready Condition.
ReadyReplicas int32 `json:"readyReplicas"`
// LabelSelector is label selectors for query over pods that should match the replica count used by HPA.
LabelSelector string `json:"labelSelector,omitempty"`
}
另外需要添加scale接口
//+kubebuilder:subresource:scale:specpath=.spec.replicas,statuspath=.status.replicas,selectorpath=.status.labelSelector
添加kubectl展示参数
//+kubebuilder:printcolumn:name="Phase",type="string",JSONPath=".status.phase",description="The phase of game."
//+kubebuilder:printcolumn:name="Host",type="string",JSONPath=".spec.host",description="The Host Address."
//+kubebuilder:printcolumn:name="DESIRED",type="integer",JSONPath=".spec.replicas",description="The desired number of pods."
//+kubebuilder:printcolumn:name="CURRENT",type="integer",JSONPath=".status.replicas",description="The number of currently all pods."
//+kubebuilder:printcolumn:name="READY",type="integer",JSONPath=".status.readyReplicas",description="The number of pods ready."
//+kubebuilder:printcolumn:name="AGE",type="date",JSONPath=".metadata.creationTimestamp",description="CreationTimestamp is a timestamp representing the server time when this object was created. It is not guaranteed to be set in happens-before order across separate operations. Clients may not set this value. It is represented in RFC3339 form and is in UTC."
编写 Controller 逻辑
Controller 的核心逻辑在Reconcile中，我们只需要填充自己的业务逻辑
func (r *GameReconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
logger := log.FromContext(ctx)
logger.Info("revice reconcile event", "name", req.String())
// 获取game对象
game := &myappv1.Game{}
if err := r.Get(ctx, req.NamespacedName, game); err != nil {
return ctrl.Result{}, client.IgnoreNotFound(err)
}
// 如果处在删除中直接跳过
if game.DeletionTimestamp != nil {
logger.Info("game in deleting", "name", req.String())
return ctrl.Result{}, nil
}
// 同步资源，如果资源不存在创建deployment、ingress、service，并更新status
if err := r.syncGame(ctx, game); err != nil {
logger.Error(err, "failed to sync game", "name", req.String())
return ctrl.Result{}, nil
}
return ctrl.Result{}, nil
}
添加 rbac 配置
//+kubebuilder:rbac:groups=apps,resources=deployments,verbs=get;list;watch;create;update;patch;delete
//+kubebuilder:rbac:groups=apps,resources=deployments/status,verbs=get;update;patch
//+kubebuilder:rbac:groups=core,resources=services,verbs=get;list;watch;create;update;patch;delete
//+kubebuilder:rbac:groups=networking,resources=ingresses,verbs=get;list;watch;create;update;patch;delete
具体syncGame逻辑如下
func (r *GameReconciler) syncGame(ctx context.Context, obj *myappv1.Game) error {
logger := log.FromContext(ctx)
game := obj.DeepCopy()
name := types.NamespacedName{
Namespace: game.Namespace,
Name: game.Name,
}
// 构造owner
owner := []metav1.OwnerReference{
{
APIVersion: game.APIVersion,
Kind: game.Kind,
Name: game.Name,
Controller: pointer.BoolPtr(true),
BlockOwnerDeletion: pointer.BoolPtr(true),
UID: game.UID,
},
}
labels := game.Labels
labels[gameLabelName] = game.Name
meta := metav1.ObjectMeta{
Name: game.Name,
Namespace: game.Namespace,
Labels: labels,
OwnerReferences: owner,
}
// 获取对应deployment, 如不存在则创建
deploy := &appsv1.Deployment{}
if err := r.Get(ctx, name, deploy); err != nil {
if !errors.IsNotFound(err) {
return err
}
deploy = &appsv1.Deployment{
ObjectMeta: meta,
Spec: getDeploymentSpec(game, labels),
}
if err := r.Create(ctx, deploy); err != nil {
return err
}
logger.Info("create deployment success", "name", name.String())
} else {
// 如果存在对比和game生成的deployment是否一致，不一致则更新
want := getDeploymentSpec(game, labels)
get := getSpecFromDeployment(deploy)
if !reflect.DeepEqual(want, get) {
deploy = &appsv1.Deployment{
ObjectMeta: meta,
Spec: want,
}
if err := r.Update(ctx, deploy); err != nil {
return err
}
logger.Info("update deployment success", "name", name.String())
}
}
//service创建
svc := &corev1.Service{}
if err := r.Get(ctx, name, svc); err != nil {
...
}
// ingress创建
ing := &networkingv1.Ingress{}
if err := r.Get(ctx, name, ing); err != nil {
...
}
newStatus := myappv1.GameStatus{
Replicas: *game.Spec.Replicas,
ReadyReplicas: deploy.Status.ReadyReplicas,
}
if newStatus.Replicas == newStatus.ReadyReplicas {
newStatus.Phase = myappv1.Running
} else {
newStatus.Phase = myappv1.NotReady
}
// 更新状态
if !reflect.DeepEqual(game.Status, newStatus) {
game.Status = newStatus
logger.Info("update game status", "name", name.String())
return r.Client.Status().Update(ctx, game)
}
return nil
}
默认情况下生成的 controller 只监听自定义资源，在示例中我们也需要监听game的子资源，如监听deployment是否符合预期
// SetupWithManager sets up the controller with the Manager.
func (r *GameReconciler) SetupWithManager(mgr ctrl.Manager) error {
// 创建controller
c, err := controller.New("game-controller", mgr, controller.Options{
Reconciler: r,
MaxConcurrentReconciles: 3, //controller运行的worker数
})
if err != nil {
return err
}
//监听自定义资源
if err := c.Watch(&source.Kind{Type: &myappv1.Game{}}, &handler.EnqueueRequestForObject{}); err != nil {
return err
}
//监听deployment,将owner信息即game namespace/name添加到队列
if err := c.Watch(&source.Kind{Type: &appsv1.Deployment{}}, &handler.EnqueueRequestForOwner{
OwnerType: &myappv1.Game{},
IsController: true,
}); err != nil {
return err
}
return nil
}
部署验证
安装 CRD
make install
本地运行 operator
make run
修改 sample 文件config/samples/myapp_v1_game.yaml
apiVersion: myapp.qingwave.github.io/v1
kind: Game
metadata:
name: game-sample
spec:
replicas: 1
image: alexwhen/docker-2048
host: mygame.io
部署game-sample
kubectl apply -f config/samples/myapp_v1_game.yaml
查看game自定义资源状态
# 查看game
kubectl get game
NAME PHASE HOST DESIRED CURRENT READY AGE
game-sample Running mygame.io 1 1 1 6m
# 查看deploy
kubectl get deploy game-sample
NAME READY UP-TO-DATE AVAILABLE AGE
game-sample 1/1 1 1 6m
# 查看ingress
kubectl get ing game-sample
NAME CLASS HOSTS ADDRESS PORTS AGE
game-sample <none> mygame.io 192.168.49.2 80 7m
验证应用，在/etc/hosts中添加<Ingress ADDRESS Ip> mygame.io，访问浏览器如下图所示 
验证扩容
kubectl scale games.myapp.qingwave.github.io game-sample --replicas 2
game.myapp.qingwave.github.io/game-sample scaled
# 扩容后
kubectl get games.myapp.qingwave.github.io
NAME PHASE HOST DESIRED CURRENT READY AGE
game-sample Running mygame.io 2 2 2 7m
如需部署Operator到集群中，可参考官方文档，制作镜像并上传，运行make deploy
Webhook
通常我们需要与 CR 自定义资源设置部分字段的默认值，或者验证字段是否合法，这就需要自己实现Webhook，Kubebuilder也提供了Webhook的功能。
通过设置--defaulting可创建mutatingadmissionwebhook类型准入控制器，用来修改传入资源；参数--programmatic-validation可创建validatingadmissionwebhook，用来验证传入资源
在资源创建、修改时
apiserver会通过 http 调用webhook提供的接口，所以会带来额外开销，简单的验证工作可通过//+kubebuilder:validation注解，直接通过openapi验证，性能更好
kubebuilder create webhook --group myapp --version v1 --kind Game --defaulting --programmatic-validation
生成文件在api/v1/game_webhook.go
Default接口可实现修改资源，根据 kubebuilder 注释,当game资源create与update时，调用这个接口
//+kubebuilder:webhook:path=/mutate-myapp-qingwave-github-io-v1-game,mutating=true,failurePolicy=fail,sideEffects=None,groups=myapp.qingwave.github.io,resources=games,verbs=create;update,versions=v1,name=mgame.kb.io,admissionReviewVersions={v1,v1beta1}
const (
defaultImage = `alexwhen/docker-2048`
)
// Default implements webhook.Defaulter so a webhook will be registered for the type
func (r *Game) Default() {
gamelog.Info("default", "name", r.Name)
// 设置默认镜像
if r.Spec.Image == "" {
r.Spec.Image = defaultImage
}
// 设置默认Host
if r.Spec.Host == "" {
r.Spec.Host = fmt.Sprintf("%s.%s.mygame.io", r.Name, r.Namespace)
}
}
同样的通过ValidateCreate、ValidateUpdate可实现validating webhook
func (r *Game) ValidateCreate() error {
gamelog.Info("validate create", "name", r.Name)
// Host不能包括通配符
if strings.Contains(r.Spec.Host, "*") {
return errors.New("host should not contain *")
}
return nil
}
本地验证 webhook 需要配置证书，在集群中测试更方便点，可参考官方文档。
总结
至此，我们已经实现了一个功能完全的game-operator，可以管理game资源的生命周期，创建/更新 game 时会自动创建deployment、service、ingress等资源，当deployment被误删或者误修改时也可以自动回复到期望状态，也实现了scale接口。
通过kubebuiler大大简化了开发operator的成本，我们只需要关心业务逻辑即可，不需要再手动去创建client/controller等，但同时kubebuilder生成的代码中屏蔽了很多细节，比如controller的最大 worker 数、同步时间、队列类型等参数设置，只有了解operator的原理才更好应用于生产。