Kubernetes(1) - operator 初体验

本章参考operator-sdk的tutorial编写一个memcache的operator

1 功能介绍

memcache operator创建成功后，可以通过如下yaml来创建进一个memcache 服务

apiVersion: cache.example.com/v1alpha1
kind: Memcached
metadata:
  name: memcached-sample
spec:
  size: 3

根据yaml创建memcached

kubectl create -f memcached.yaml

创建成功后，可以通过kubectl 查看memcached的状态信息

# 查看是否存在对应资源信息
tingshuai.yts@B-5BBCMD6M-2026 ~ % kubectl get memcached
NAME               AGE
memcached-sample   34m

# 查看memcached详细信息
tingshuai.yts@B-5BBCMD6M-2026 ~ % kubectl get memcached memcached-sample -o yaml
apiVersion: cache.example.com/v1alpha1
kind: Memcached
metadata:
  creationTimestamp: "2022-02-24T07:16:33Z"
  generation: 2
  name: memcached-sample
  namespace: default
  resourceVersion: "3385066472"
  selfLink: /apis/cache.example.com/v1alpha1/namespaces/default/memcacheds/memcached-sample
  uid: 12f26a9f-fc34-492e-a30f-bc17266052aa
spec:
  size: 4
status:
  nodes:
  - memcached-sample-9b765dfc8-w6l26
  - memcached-sample-9b765dfc8-7cwpl
  - memcached-sample-9b765dfc8-kxnmd
  - memcached-sample-9b765dfc8-hsrqd

memcached operator主要工作是根据yaml中的描述spec来创建deployment，如下所示：

tingshuai.yts@B-5BBCMD6M-2026 ~ % kubectl get deploy
NAME               READY   UP-TO-DATE   AVAILABLE   AGE
memcached-sample   4/4     4            4           37m

2 整体流程

编写一个operator一般分为如下几个步骤：

• 开发环境搭建
• 通过operator sdk创建operator project
• 通过operator sdk创建API和controller 框架代码
• 编写API和controller业务代码
• 调试执行

3 环境搭建

开发controller依赖如下环境，由于篇幅有限，本文仅列举依赖的内容，安装方式读者自行百度即可

• golang
• operator-sdk
• kubectl 和k8s对应的config

4 创建operator project

通过operator-sdk init命令创建controller的project

mkdir -p $HOME/projects/memcached-operator
cd $HOME/projects/memcached-operator

# we'll use a domain of example.com
# so all API groups will be .example.com
operator-sdk init --domain example.com --repo github.com/example/memcached-operator

operator-sdk init的帮助文档信息如下：

% operator-sdk init --help
Initialize a new project including the following files:
  - a "go.mod" with project dependencies
  - a "PROJECT" file that stores project configuration
  - a "Makefile" with several useful make targets for the project
  - several YAML files for project deployment under the "config" directory
  - a "main.go" file that creates the manager that will run the project controllers

Usage:
  operator-sdk init [flags]

Examples:
  # Initialize a new project with your domain and name in copyright
  operator-sdk init --plugins go/v3 --domain example.org --owner "Your name"

  # Initialize a new project defining an specific project version
  operator-sdk init --plugins go/v3 --project-version 3


Flags:
      --component-config         create a versioned ComponentConfig file, may be 'true' or 'false'
      --domain string            domain for groups (default "my.domain")
      --fetch-deps               ensure dependencies are downloaded (default true)
  -h, --help                     help for init
      --license string           license to use to boilerplate, may be one of 'apache2', 'none' (default "apache2")
      --owner string             owner to add to the copyright
      --project-name string      name of this project
      --project-version string   project version (default "3")
      --repo string              name to use for go module (e.g., github.com/user/repo), defaults to the go package of the current working directory.
      --skip-go-version-check    if specified, skip checking the Go version

Global Flags:
      --plugins strings   plugin keys to be used for this subcommand execution
      --verbose           Enable verbose logging

5 创建API和controller框架代码

执行下面的命令会创建api和controller的框架代码，然后我们在框架代码的基础上按照需求填写业务逻辑代码即可：

• api代码会在api/v1alpha1/memcached_types.go
• controller代码会在controllers/memcached_controller.go

$ operator-sdk create api --group cache --version v1alpha1 --kind Memcached --resource --controller

6 编写API

6.1 api 定义

创建完api后代码，operator sdk生成的主要代码如下：

// MemcachedSpec defines the desired state of Memcached
type MemcachedSpec struct {
        // INSERT ADDITIONAL SPEC FIELDS - desired state of cluster
        // Important: Run "make" to regenerate code after modifying this file

        // Foo is an example field of Memcached. Edit memcached_types.go to remove/update
        Foo string `json:"foo,omitempty"`
}

// MemcachedStatus defines the observed state of Memcached
type MemcachedStatus struct {
        // INSERT ADDITIONAL STATUS FIELD - define observed state of cluster
        // Important: Run "make" to regenerate code after modifying this file
}

//+kubebuilder:object:root=true
//+kubebuilder:subresource:status

// Memcached is the Schema for the memcacheds API
type Memcached struct {
        metav1.TypeMeta   `json:",inline"`
        metav1.ObjectMeta `json:"metadata,omitempty"`

        Spec   MemcachedSpec   `json:"spec,omitempty"`
        Status MemcachedStatus `json:"status,omitempty"`
}

一般来说，我们需要修改spec和status的定义，来满足我们的业务需求。

spec更改如下：

• 添加Size字段，用来定义memcache 副本的个数
• +kubebuilder:validation:Minimum=0 是marker comments；operator-sdk会根据marker comments的描述来生成代码。本例中marker comments的作用是生成api定义的校验代码，如果spec的小于0，则validation检查会失败（下一节会对marker comments进一步介绍）

// MemcachedSpec defines the desired state of Memcached
type MemcachedSpec struct {
	//+kubebuilder:val