Data Passing

This section introduces how to use Inputs and Outputs to pass data between workflow steps in KubeVela.

Outputs

Outputs consists of name and valueFrom. name declares the name of this output, which will be referenced by from in input.

valueFrom can be written in the following ways:

1. Use value expression, eg. valueFrom: output.value.status.workflow.message. Note that output.value.status.workflow.message will use the value of the variable from the CUE template of the current step. If this field does not exist in the CUE template of the step, the resulting value will be empty.
2. Use CUE expressions, eg. use + to combine value and string: valueFrom: output.metadata.name + "testString" or you can import built-in packages in CUE like:

valueFrom: |
          import "strings"
          strings.Join(["1","2"], ",")

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.

caution

If you want to set the parameterKey with a invalid CUE variable name (eg: contains -, or starts with a number, etc.), you can refer to it with [] like:

inputs:
   - from: output
     parameterKey: data["my-input"]

eg. Specify inputs:

...
- name: notify
  type: notification
  inputs:
    - from: read-status
      parameterKey: slack.message.text

How to use

Suppose we already have a depends application in the cluster, and we want to read the workflow status of the depends Application in a new Application and send the status information to Slack.

Apply the following YAML:

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
  name: input-output
  namespace: default
spec:
  components:
  - name: express-server
    type: webservice
    properties:
      image: oamdev/hello-world
      ports:
        - port: 8000
  workflow:
    steps:
      - name: read
        type: read-object
        properties:
          name: depends
        outputs:
          - name: read-status
            valueFrom: output.value.status.workflow.message
      - name: slack-message
        type: notification
        inputs:
          - from: read-status
            parameterKey: slack.message.text
        properties:
          slack:
            url:
              value: <your slack url>

When reading the depends application, we use the read-object step type. In this step type, the read resources will be placed in output.value, so we can use output.value.status.workflow.message reads the workflow status information of depends.

When the application runs successfully, we can receive the workflow status information of the depends application in the Slack message notification.