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Version: v1.1

How-to

In this section we will introduce how to define a trait.

Simple Trait#

A trait in KubeVela can be defined by simply reference a existing Kubernetes API resource.

apiVersion: core.oam.dev/v1beta1
kind: TraitDefinition
metadata:
name: ingress
spec:
definitionRef:
name: ingresses.networking.k8s.io

Let's attach this trait to a component instance in Application:

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
name: testapp
spec:
components:
- name: express-server
type: webservice
properties:
cmd:
- node
- server.js
image: oamdev/testapp:v1
port: 8080
traits:
- type: ingress
properties:
rules:
- http:
paths:
- path: /testpath
pathType: Prefix
backend:
service:
name: test
port:
number: 80

Note that in this case, all fields in the referenced resource's spec will be exposed to end user and no metadata (e.g. annotations etc) are allowed to be set trait properties. Hence this approach is normally used when you want to bring your own CRD and controller as a trait, and it dose not rely on annotations etc as tuning knobs.

Using CUE as Trait Schematic#

The recommended approach is defining a CUE based schematic for trait as well. In this case, it comes with abstraction and you have full flexibility to templating any resources and fields as you want. Note that KubeVela requires all traits MUST be defined in outputs section (not output) in CUE template with format as below:

outputs: <unique-name>:
<full template data>

Below is an example for ingress trait.

apiVersion: core.oam.dev/v1beta1
kind: TraitDefinition
metadata:
name: ingress
spec:
podDisruptive: false
schematic:
cue:
template: |
parameter: {
domain: string
http: [string]: int
}
// trait template can have multiple outputs in one trait
outputs: service: {
apiVersion: "v1"
kind: "Service"
spec: {
selector:
app: context.name
ports: [
for k, v in parameter.http {
port: v
targetPort: v
},
]
}
}
outputs: ingress: {
apiVersion: "networking.k8s.io/v1beta1"
kind: "Ingress"
metadata:
name: context.name
spec: {
rules: [{
host: parameter.domain
http: {
paths: [
for k, v in parameter.http {
path: k
backend: {
serviceName: context.name
servicePort: v
}
},
]
}
}]
}
}

Let's attach this trait to a component instance in Application:

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
name: testapp
spec:
components:
- name: express-server
type: webservice
properties:
cmd:
- node
- server.js
image: oamdev/testapp:v1
port: 8080
traits:
- type: ingress
properties:
domain: test.my.domain
http:
"/api": 8080

CUE based trait definitions can also enable many other advanced scenarios such as patching and data passing. They will be explained in detail in the following documentations.

Last updated on by yangsoon