kubevela.github.io/docs/end-user/workflow/component-dependency-parameter.md

title
Data Passing

This section will introduce how to pass data between components.

Inputs and Outputs

In KubeVela, we can use inputs and outputs in Components to pass data.

Outputs

Outputs is made of name and valueFrom. Input will use name to reference output.

We can write valueFrom in the following ways:

1. Fill string value in the field, eg. valueFrom: testString.
2. Use expression, eg. valueFrom: output.metadata.name. Note that output is a built-in field referring to the resource in the component that is rendered and deployed to the cluster.
3. Use + to combine above two ways, the computed value will be the result, eg. valueFrom: output.metadata.name + "testString".

Inputs

Inputs is made of from and parameterKey. Input uses from to reference output, parameterKey is a expression that assigns the value of the input to the corresponding field.

eg.

1. Specify inputs:

...
- name: wordpress
  type: helm
  inputs:
    - from: mysql-svc
      parameterKey: properties.values.externalDatabase.host

2. The field parameterKey specifies the field path of the parameter key in component to be assigned after rendering:

Which means the input value will be passed into the below properties:

...
- name: wordpress
  type: helm
  properties:
    values:
      externalDatabase:
        host: <input value>

How to use

In the following we will apply a WordPress server with the MySQL address passed from a MySQL component:

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
  name: wordpress-with-mysql
  namespace: default
spec:
  components:
    - name: mysql
      type: helm
      outputs:
        # the output is the mysql service address
        - name: mysql-svc
          exportKey: output.metadata.name + ".default.svc.cluster.local"
      properties:
        repoType: helm
        url: https://charts.bitnami.com/bitnami
        chart: mysql
        version: "8.8.2"
        values:
          auth:
            rootPassword: mypassword
    - name: wordpress
      type: helm
      inputs:
        # set the host to mysql service address
        - from: mysql-svc
          parameterKey: properties.values.externalDatabase.host
      properties:
        repoType: helm
        url: https://charts.bitnami.com/bitnami
        chart: wordpress
        version: "12.0.3"
        values:
          mariadb:
            enabled: false
          externalDatabase:
            user: root
            password: mypassword
            database: mysql
            port: 3306

Expected Outcome

The WordPress with MySQL has been successfully applied.