Component Definition
In this section, we will introduce how to use CUE to customize components via ComponentDefinition. Make sure you've learned the basic knowledge about Definition Concept and how to manage definition.
Declare ComponentDefinition
First, generate ComponentDefinition scaffolds via vela def init with existed YAML file.
The YAML file:
apiVersion: "apps/v1"
kind: "Deployment"
spec:
selector:
matchLabels:
"app.oam.dev/component": "name"
template:
metadata:
labels:
"app.oam.dev/component": "name"
spec:
containers:
- name: "name"
image: "image"
Generate ComponentDefinition based on the YAML file:
vela def init stateless -t component --template-yaml ./stateless.yaml -o stateless.cue
It generates a file:
stateless: {
annotations: {}
attributes: workload: definition: {
apiVersion: "<change me> apps/v1"
kind: "<change me> Deployment"
}
description: ""
labels: {}
type: "component"
}
template: {
output: {
spec: {
selector: matchLabels: "app.oam.dev/component": "name"
template: {
metadata: labels: "app.oam.dev/component": "name"
spec: containers: [{
name: "name"
image: "image"
}]
}
}
apiVersion: "apps/v1"
kind: "Deployment"
}
outputs: {}
parameter: {}
}
In detail:
- The
statelessis the name of component definition, it can be defined by yourself when initialize the component. stateless.attributes.workloadindicates the workload type of this component, it can help integrate with traits that apply to this kind of workload.templateis a CUE template, specifically:- The
outputandoutputsfields define the resources that the component will be composed. - The
parameterfield defines the parameters of the component, i.e. the configurable properties exposed in theApplication(and schema will be automatically generated based on them for end users to learn this component).
- The
Add parameters in this auto-generated custom component file :
stateless: {
annotations: {}
attributes: workload: definition: {
apiVersion: "apps/v1"
kind: "Deployment"
}
description: ""
labels: {}
type: "component"
}
template: {
output: {
spec: {
selector: matchLabels: "app.oam.dev/component": parameter.name
template: {
metadata: labels: "app.oam.dev/component": parameter.name
spec: containers: [{
name: parameter.name
image: parameter.image
}]
}
}
apiVersion: "apps/v1"
kind: "Deployment"
}
outputs: {}
parameter: {
name: string
image: string
}
}
You can use vela def vet to validate the format:
vela def vet stateless.cue
expected output
Validation succeed.
Apply above ComponentDefinition to your Kubernetes cluster to make it work:
vela def apply stateless.cue
expected output
ComponentDefinition stateless created in namespace vela-system.
Then the end user can check the schema and use it in an application now:
vela show stateless
expected output
# Specification
+-------+-------------+--------+----------+---------+
| NAME | DESCRIPTION | TYPE | REQUIRED | DEFAULT |
+-------+-------------+--------+----------+---------+
| name | | string | true | |
| image | | string | true | |
+-------+-------------+--------+----------+---------+
Declare another component named task which is an abstraction for run-to-completion workload works the same.
Check the details for another example to define a task based component.
vela def init task -t component -o task.cue
It generates a file:
// $ cat task.cue
task: {
annotations: {}
attributes: workload: definition: {
apiVersion: "<change me> apps/v1"
kind: "<change me> Deployment"
}
description: ""
labels: {}
type: "component"
}
template: {
output: {}
parameter: {}
}
Edit the generated component file:
task: {
annotations: {}
attributes: workload: definition: {
apiVersion: "batch/v1"
kind: "Job"
}
description: ""
labels: {}
type: "component"
}
template: {
output: {
apiVersion: "batch/v1"
kind: "Job"
spec: {
parallelism: parameter.count
completions: parameter.count
template: spec: {
restartPolicy: parameter.restart
containers: [{
image: parameter.image
if parameter["cmd"] != _|_ {
command: parameter.cmd
}
}]
}
}
}
parameter: {
count: *1 | int
image: string
restart: *"Never" | string
cmd?: [...string]
}
}
Apply above ComponentDefinition files to your Kubernetes cluster to make it work:
$ vela def apply task.cue
ComponentDefinition task created in namespace vela-system.
Now let's use the stateless and task component type.
Declare an Application using this component
The ComponentDefinition can be instantiated in Application abstraction as below:
apiVersion: core.oam.dev/v1alpha2
kind: Application
metadata:
name: website
spec:
components:
- name: hello
type: stateless
properties:
image: oamdev/hello-world
name: mysvc
- name: countdown
type: task
properties:
image: centos:7
cmd:
- "bin/bash"
- "-c"
- "for i in 9 8 7 6 5 4 3 2 1 ; do echo $i ; done"
Learn Details Under The Hood
Above application resource will generate and manage following Kubernetes resources in your target cluster based on the output in CUE template and user input in Application properties.
apiVersion: apps/v1
kind: Deployment
metadata:
name: backend
... # skip tons of metadata info
spec:
template:
spec:
containers:
- name: mysvc
image: oamdev/hello-world
metadata:
labels:
app.oam.dev/component: mysvc
selector:
matchLabels:
app.oam.dev/component: mysvc
---
apiVersion: batch/v1
kind: Job
metadata:
name: countdown
... # skip tons of metadata info
spec:
parallelism: 1
completions: 1
template:
metadata:
name: countdown
spec:
containers:
- name: countdown
image: 'centos:7'
command:
- bin/bash
- '-c'
- for i in 9 8 7 6 5 4 3 2 1 ; do echo $i ; done
restartPolicy: Never
You can also use dry run to show what the yaml results will be rendered for debugging.
CUE Context for runtime information
KubeVela allows you to reference the runtime information of your application via context keyword.
The most widely used context is application name(context.appName) component name(context.name).
context: {
appName: string
name: string
}
For example, let's say you want to use the component name filled in by users as the container name in the workload instance:
parameter: {
image: string
}
output: {
...
spec: {
containers: [{
name: context.name
image: parameter.image
}]
}
...
}
Note that context information are auto-injected before resources are applied to target cluster.
The list of all available context variables are listed at last of this doc.
Compose resources in one component
It's common that a component definition is composed by multiple API resources, for example, a webserver component that is composed by a Deployment and a Service. CUE is a great solution to achieve this in simplified primitives.
Compare to using Helm, this approach gives your more flexibility as you can control the abstraction any time and integrate with traits, workflows in KubeVela better.
KubeVela requires you to define the template of main workload in output section, and leave all the other resource templates in outputs section with format as below:
output: {
<template of main workload structural data>
}
outputs: {
<unique-name>: {
<template of auxiliary resource structural data>
}
}
The reason for this requirement is KubeVela needs to know it is currently rendering a workload so it could do some "magic" by traits such like patching annotations/labels or other data during it.
Below is the example for webserver definition, let's use a demo to show how to use it:
webserver: {
annotations: {}
attributes: workload: definition: {
apiVersion: "apps/v1"
kind: "Deployment"
}
description: ""
labels: {}
type: "component"
}
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
}
}
}]
}
}
}
}
// an extra template
outputs: service: {
apiVersion: "v1"
kind: "Service"
spec: {
selector: {
"app.oam.dev/component": context.name
}
ports: [
{
port: parameter.port
targetPort: parameter.port
},
]
}
}
parameter: {
image: string
cmd?: [...string]
port: *80 | int
env?: [...{
name: string
value?: string
valueFrom?: {
secretKeyRef: {
name: string
key: string
}
}
}]
cpu?: string
}
}
Apply to your Kubernetes cluster:
vela def apply webserver.cue
expected output
ComponentDefinition webserver created in namespace vela-system.
The user could now declare an Application with it:
apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
name: webserver-demo
namespace: default
spec:
components:
- name: hello-webserver
type: webserver
properties:
image: oamdev/hello-world
port: 8000
env:
- name: "foo"
value: "bar"
cpu: "100m"
Create this application by:
vela up -f webserver-app.yaml
Then you can check the resources and find the results:
vela status webserver-demo --tree --detail
expected output
CLUSTER NAMESPACE RESOURCE STATUS APPLY_TIME DETAIL
local ─── default ─┬─ Service/hello-webserver-auxiliaryworkload-685d98b6d9 updated 2022-10-15 21:58:35 Type: ClusterIP
│ Cluster-IP: 10.43.255.55
│ External-IP: <none>
│ Port(s): 8000/TCP
│ Age: 66s
└─ Deployment/hello-webserver updated 2022-10-15 21:58:35 Ready: 1/1 Up-to-date: 1
Available: 1 Age: 66s
Define health check and status message for component
You can also define health check policy and status message when a component deployed and tell the real status to end users.
Reference parameter defined in template is not supported now in health check and custom status, they work in different stage with the resource template. While we're going to support this feature in https://github.com/kubevela/kubevela/issues/4863 .
Health check
The spec of health check is <component-type-name>.attributes.status.healthPolicy.
If not defined, the health result will always be true, which means it will be marked as healthy immediately after resources applied to Kubernetes. You can define a CUE expression in it to notify if the component is healthy or not.
The keyword is isHealth, the result of CUE expression must be bool type.
KubeVela runtime will evaluate the CUE expression periodically until it becomes healthy. Every time the controller will get all the Kubernetes resources and fill them into the context variables.
So the context will contain following information:
context:{
name: <component name>
appName: <app name>
output: <K8s workload resource>
outputs: {
<resource1>: <K8s trait resource1>
<resource2>: <K8s trait resource2>
}
}
The example of health check likes below:
webserver: {
type: "component"
...
attributes: {
status: {
healthPolicy: #"""
isHealth: (context.output.status.readyReplicas > 0) && (context.output.status.readyReplicas == context.output.status.replicas)
"""#
}
}
}
The health check result will be recorded into the corresponding component in .status.services of Application resource.
apiVersion: core.oam.dev/v1beta1
kind: Application
status:
...
services:
- healthy: true
name: myweb
...
status: running
Please refer to this doc for more examples.
Custom Status
The spec of custom status is <component-type-name>.attributes.status.customStatus, it shares the same mechanism with the health check.
The keyword in CUE expression is message, the result must be string type.
Application CRD controller will evaluate the CUE expression after the health check succeed.
The example of custom status likes below:
webserver: {
type: "component"
...
attributes: {
status: {
customStatus: #"""
ready: {
readyReplicas: *0 | int
} & {
if context.output.status.readyReplicas != _|_ {
readyReplicas: context.output.status.readyReplicas
}
}
message: "Ready:\(ready.readyReplicas)/\(context.output.spec.replicas)"
"""#
}
}
}
The message will be recorded into the corresponding component in .status.services of Application resource like below.
apiVersion: core.oam.dev/v1beta1
kind: Application
status:
...
services:
- healthy: false
message: Ready:1/1
name: express-server
Please refer to this doc for more examples.
Full available context in Component
| Context Variable | Description | Type |
|---|---|---|
context.appName | The app name corresponding to the current instance of the application. | string |
context.namespace | The target namespace of the current resource is going to be deployed, it can be different with the namespace of application if overridden by some policies. | string |
context.cluster | The target cluster of the current resource is going to be deployed, it can be different with the namespace of application if overridden by some policies. | string |
context.appRevision | The app version name corresponding to the current instance of the application. | string |
context.appRevisionNum | The app version number corresponding to the current instance of the application. | int |
context.name | The component name corresponding to the current instance of the application. | string |
context.revision | The version name of the current component instance. | string |
context.output | The object structure after instantiation of current component. | Object Map |
context.outputs.<resourceName> | Structure after instantiation of current component auxiliary resources. | Object Map |
context.workflowName | The workflow name specified in annotation. | string |
context.publishVersion | The version of application instance specified in annotation. | string |
context.appLabels | The labels of the current application instance. | Object Map |
context.appAnnotations | The annotations of the current application instance. | Object Map |
context.replicaKey | The key of replication in context. Replication is an internal policy, it will replicate resources with different keys specified. (This feature will be introduced in v1.6+.) | string |
Component definition in Kubernetes
KubeVela is fully programmable via CUE, while it leverage Kubernetes as control plane and align with the API in yaml. As a result, the CUE definition will be converted as Kubernetes API when applied into cluster.
The component definition will be in the following API format:
apiVersion: core.oam.dev/v1beta1
kind: ComponentDefinition
metadata:
name: <ComponentDefinition name>
annotations:
definition.oam.dev/description: <Function description>
spec:
workload: # Workload Capability Indicator
definition:
apiVersion: <Kubernetes Workload resource group>
kind: <Kubernetes Workload types>
schematic: # Component description
cue: # Details of components defined by CUE language
template: <CUE format template>
You can check the detail of this format here.
More examples to learn
You can check the following resources for more examples:
- Builtin component definitions in the KubeVela github repo.
- Definitions defined in addons in the catalog repo.