关于kubevela和oam

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发布于 2021-02-26 10:16:41

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发布于 2021-02-26 10:16:41

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kubevela 是 OAM 的实现，虽然是今年才发布的项目，但我们可以通过结合 kubevela 帮助我们更好地了解 OAM。

vela 安装：

$ vela install
- Installing Vela Core Chart:
created namespace vela-system
install chart vela-core, version v0.3.0, desc : A Helm chart for Kube Vela core, contains 36 file
Automatically discover capabilities successfully ✅ Add(8) Update(0) Delete(0)
⠋ Waiting Capability ready to install ... 
TYPE       	CATEGORY	DESCRIPTION                                                                     
+task      	workload	Describes jobs that run code or a script to completion.                         
+webservice	workload	Describes long-running, scalable, containerized services that have a stable     
           	        	network endpoint to receive external network traffic from customers. If workload
           	        	type is skipped for any service defined in Appfile, it will be defaulted to     
           	        	`webservice` type.                                                              
+worker    	workload	Describes long-running, scalable, containerized services that running at        
           	        	backend. They do NOT have network endpoint to receive external network          
           	        	traffic.                                                                        
+autoscale 	trait   	Automatically scales workloads by resource utilization metrics or cron          
           	        	triggers.                                                                       
+metrics   	trait   	Configures monitoring metrics for your service.                                 
+rollout   	trait   	Configures Canary deployment strategy for your application.                     
+route     	trait   	Configures external access to your service.                                     
+scaler    	trait   	Configures replicas for your service.                                           

- Finished successfully.

可以看到kubevela提供了 8 种资源，workload类型的task、webservice、worker，traint类型的autoscale，metrics，rollout，route和scaler。

这里出现了两个概念workload和traint，这是 OAM 定义的资源概念：

workload 类似于 k8s 的自定义资源（CR）的概念，用于基础设施人员自定义资源
component 用于定义应用程序的基本组件，可以理解成一个job,一个db或一个deployment，一个 Component 中只能引用一个workload
taint 可以用于定义 component 的运维属性，比如路由，限流熔断策略，由最终的ApplicationConfiguration将其和 component 组装
ApplicationConfiguration 定义了一个应用程序的配置，通过component和taint模板，定义一个具体的运行实例

可以看到 OAM 核心就是组合和装配。

简单了解了 OAM 的几个概念之后，我们来看看 kubevela 提供哪些 workload:

$ kubectl get WorkloadDefinition
NAME         DEFINITION-NAME
task         jobs.batch
webservice   deployments.apps
worker       deployments.apps

vela 提供了三种 workload： task， webservice, worker。其中 task 对应 k8s 中的 job.batch，webservice 和 worker 都是 deployments， webservice 提供更多能力，比如端口，环境变量，config设置等，下面是 webservice 的 workloadDefinition 定义:

$ kubectl get WorkloadDefinition webservice -oyaml | yq r - spec.extension.template
output: {
	apiVersion: "apps/v1"
	kind:       "Deployment"
	spec: {
		selector: matchLabels: {
			"app.oam.dev/component": context.name
		}

		template: {
			metadata: labels: {
				"app.oam.dev/component": context.name
			}

			spec: {
				containers: [{
					name:  context.name
					image: parameter.image

					if parameter["cmd"] != _|_ {
						command: parameter.cmd
					}

					if parameter["env"] != _|_ {
						env: parameter.env
					}

					if context["config"] != _|_ {
						env: context.config
					}

					ports: [{
						containerPort: parameter.port
					}]

					if parameter["cpu"] != _|_ {
						resources: {
							limits:
								cpu: parameter.cpu
							requests:
								cpu: parameter.cpu
						}
					}
				}]
		}
		}
	}
}
parameter: {
	// +usage=Which image would you like to use for your service
	// +short=i
	image: string

	// +usage=Commands to run in the container
	cmd?: [...string]

	// +usage=Which port do you want customer traffic sent to
	// +short=p
	port: *80 | int
	// +usage=Define arguments by using environment variables
	env?: [...{
		// +usage=Environment variable name
		name: string
		// +usage=The value of the environment variable
		value?: string
		// +usage=Specifies a source the value of this var should come from
		valueFrom?: {
			// +usage=Selects a key of a secret in the pod's namespace
			secretKeyRef: {
				// +usage=The name of the secret in the pod's namespace to select from
				name: string
				// +usage=The key of the secret to select from. Must be a valid secret key
				key: string
			}
		}
	}]
	// +usage=Number of CPU units for the service, like `0.5` (0.5 CPU core), `1` (1 CPU core)
	cpu?: string
}

提供的traits:

$ kubectl get traitDefinitions
NAME        DEFINITION-NAME
autoscale   autoscalers.standard.oam.dev
metrics     metricstraits.standard.oam.dev
rollout     canaries.flagger.app
route       routes.standard.oam.dev
scaler      manualscalertraits.core.oam.dev

vela 提供了五种 trait，自动扩容，metrics指标，回滚，路由和手动扩容，以最常见的 route 为例，我们看看 traits 的定义：

$ kubectl get traitDefinitions route -oyaml   | yq r - spec.extension.template
output: {
	apiVersion: "standard.oam.dev/v1alpha1"
	kind:       "Route"
	spec: {
		host: parameter.domain

		if parameter.issuer != "" {
			tls: {
				issuerName: parameter.issuer
			}
		}

		if parameter["rules"] != _|_ {
			rules: parameter.rules
		}

		provider: *"nginx" | parameter.provider
	}
}
parameter: {
	// +usage= Domain name
	domain: *"" | string

	issuer: *"" | string
	rules?: [...{
		path:          string
		rewriteTarget: *"" | string
	}]
	provider?: string
}

最后是 scopes， scopes 表示作用域，主要用于分组和管理，比如可以将一个 component 划归到多个 scopes，一个scopes 也可以包含多个 component，因为在日常中 scopes 概念用的比较，因为用的比较少，这里就不细讲了，vela 提供了一个 healthscopes :

$ kubectl get scopedefinitions
NAME                        DEFINITION-NAME
healthscopes.core.oam.dev   healthscopes.core.oam.dev

了解 OAM 应用的基本组成之后，我们基于 vela 来创建一个 Application ，并看他如何创建的。

vela 创建应用

我们构建一个webservice应用，这里就使用官方提供的案例：

$ cat vela.yaml
name: first-vela-app
services:
  testsvc:
    type: webservice
    image: crccheck/hello-world
    port: 8000
    route:
      domain: testsvc.example.com
$ vela up -f vela.yaml
Parsing vela appfile ...
Load Template ...

Rendering configs for service (testsvc)...
Writing deploy config to (.vela/deploy.yaml)

Applying application ...
Checking if app has been deployed...
App has not been deployed, creating a new deployment...
✅ App has been deployed ???
    Port forward: vela port-forward first-vela-app
             SSH: vela exec first-vela-app
         Logging: vela logs first-vela-app
      App status: vela status first-vela-app
  Service status: vela status first-vela-app --svc testsvc

vela 会将 Appfile 渲染成 Application资源。

我们看看 website 的Application：

# kubectl get Application  first-vela-app -oyaml
apiVersion: core.oam.dev/v1alpha2
kind: Application
metadata:
  creationTimestamp: "2021-01-26T08:24:53Z"
  generation: 1
  name: first-vela-app
  namespace: default
  resourceVersion: "2662687"
  selfLink: /apis/core.oam.dev/v1alpha2/namespaces/default/applications/first-vela-app
  uid: a603e28a-b52a-4b5f-ae6c-be57de887c51
spec:
  components:
  - name: testsvc
    scopes:
      healthscopes.core.oam.dev: first-vela-app-default-health
    settings:
      image: crccheck/hello-world
      port: 8000
    traits:
    - name: route
      properties:
        domain: testsvc.example.com
    type: webservice

这个 Application 是 kubevela 的 appfile 服务端映射，其下层实现是由 ApplicationConfiguration 来做的。

我们可以看看ApplicationConfiguration：

apiVersion: core.oam.dev/v1alpha2
kind: ApplicationConfiguration
metadata:
  creationTimestamp: "2021-01-26T04:23:03Z"
  finalizers:
  - scope.finalizer.core.oam.dev
  generation: 1
  labels:
    application.oam.dev: first-vela-app
  name: first-vela-app
  namespace: default
  ownerReferences:
  - apiVersion: core.oam.dev/v1alpha2
    controller: true
    kind: Application
    name: first-vela-app
    uid: 5b2c0284-0bd1-4c4c-a671-0fa8c7684b26
  resourceVersion: "39680262"
  selfLink: /apis/core.oam.dev/v1alpha2/namespaces/default/applicationconfigurations/first-vela-app
  uid: 00bc284d-c57f-4b52-a177-31753520c619
spec:
  components:
  - componentName: testsvc
    scopes:
    - scopeRef:
        apiVersion: core.oam.dev/v1alpha2
        kind: HealthScope
        name: first-vela-app-default-health
    traits:
    - trait:
        apiVersion: standard.oam.dev/v1alpha1
        kind: Route
        metadata:
          labels:
            trait.oam.dev/type: route
        spec:
          host: testsvc.example.com
          provider: nginx
status:
  conditions:
  - lastTransitionTime: "2021-01-31T22:49:03Z"
    reason: ReconcileSuccess
    status: "True"
    type: Synced
  dependency: {}
  observedGeneration: 1
  workloads:
  - componentName: testsvc
    componentRevisionName: testsvc-v3
    scopes:
    - scopeRef:
        apiVersion: core.oam.dev/v1alpha2
        kind: HealthScope
        name: first-vela-app-default-health
    traits:
    - traitRef:
        apiVersion: standard.oam.dev/v1alpha1
        kind: Route
        name: testsvc-route-c4575497d
    workloadRef:
      apiVersion: apps/v1
      kind: Deployment
      name: testsvc

包含了一个 testsvc 的component，这个 component 包含了一个 scopes 和 traits。 application 会根据 type 配置从 workload模板中创建一个 component，我们看看 testsvc 的 component:

# kubectl get components testsvc -oyaml
apiVersion: core.oam.dev/v1alpha2
kind: Component
metadata:
  creationTimestamp: "2021-01-26T08:24:55Z"
  generation: 1
  labels:
    application.oam.dev: first-vela-app
  name: testsvc
  namespace: default
  ownerReferences:
  - apiVersion: core.oam.dev/v1alpha2
    controller: true
    kind: Application
    name: first-vela-app
    uid: a603e28a-b52a-4b5f-ae6c-be57de887c51
  resourceVersion: "2662686"
  selfLink: /apis/core.oam.dev/v1alpha2/namespaces/default/components/testsvc
  uid: eb6a8f1a-c8e5-4140-b5e8-ad5864862c4b
spec:
  workload:
    apiVersion: apps/v1
    kind: Deployment
    metadata:
      labels:
        workload.oam.dev/type: webservice
    spec:
      selector:
        matchLabels:
          app.oam.dev/component: testsvc
      template:
        metadata:
          labels:
            app.oam.dev/component: testsvc
        spec:
          containers:
          - image: crccheck/hello-world
            name: testsvc
            ports:
            - containerPort: 8000

我们可以看到ApplicationConfiguration 和 Component 这两个资源都有 ownerReferences，在 owner 资源被删除的时候，Kubernetes 垃圾收集器会自动将附属的资源清除。

小结

OAM 提供了三种核心的模板来创建一个应用， components，traits 和 scopes，components 一般定义一些和基础设施相关模板，由平台团队提供，traits 定义和基础运维相关模板，由运维人员定义，scopes 偏向于两者都关心的部分。通过将应用拆分成不同的层次，让各部分只关注自己的那个专注的那个点，而不用对全局的关注。

vela 算是 OAM 的一种落地实现，定义几种通用的资源（worker,webservices,routes…），再通过 Appfile 渲染生成 Application。本质上和基于 helm 开发一套符合 OAM 标准的模板依赖一样，不过 vela 是运行在集群内部，对应用会更强的控制，和 helm 这种从集群中退下来(v3去掉tiller)变成纯粹部署工具的理念还是有些区别的。

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原始发表：2021-01-24，如有侵权请联系 cloudcommunity@tencent.com 删除

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