kubevela.github.io/docs/platform-engineers/workflow/data-flow.md

title
Data Flow

What's Data Flow

In KubeVela, data flow enables users to pass data from one workflow step to another. You can orchestrate the data flow by specifying declarative config -- inputs and outputs of each step. This doc will explain how to specify data inputs and outputs.

Full example available at: https://github.com/oam-dev/kubevela/blob/master/docs/examples/workflow

Outputs

An output exports the data corresponding to a key in the CUE template of a workflow step. Once the workflow step has finished running, the output will have the data from the key.

Here is an example to specify the output in Application:

apiVersion: core.oam.dev/v1beta1
kind: Application
spec:
  ...
  workflow:
    steps:
      - name: deploy-server1
        type: apply-component
        properties:
          component: "server1"
        outputs:
          - name: server1IP
            # Any key can be exported from the CUE template of the Definition
            exportKey: "myIP"

Here is an example CUE template that contains the export key:

apiVersion: core.oam.dev/v1beta1
kind: WorkflowStepDefinition
metadata:
  name: apply-component
spec:
  schematic:
    cue:
      template: |
        import ("vela/op")
        parameter: {
          component: string
        }
        // load component from application
        component: op.#Load & {
          component: parameter.component
        }
        // apply workload to Kubernetes cluster
        apply: op.#ApplyComponent & {
          component: parameter.component
        }
        // export podIP
        myIP: apply.workload.status.podIP        

The output can then be used by the input in the following.

Inputs

An input takes the data of an output to fill a parameter in the CUE template of a workflow step. The parameter will be filled before running the workflow step.

Here is an example to specify the input in Application:

kind: Application
spec:
  ...
  workflow:
    steps:
      ...
      - name: deploy-server2
        type: apply-with-ip
        inputs:
          - from: server1IP
            parameterKey: serverIP
        properties:
          component: "server2"

Here is an example CUE template that takes the input parameter:

apiVersion: core.oam.dev/v1beta1
kind: WorkflowStepDefinition
metadata:
  name: apply-with-ip
spec:
  schematic:
    cue:
      template: |
        import ("vela/op")
        parameter: {
          component: string
          // the input value will be used to fill this parameter
          serverIP?: string
        }
        // load component from application
        component: op.#Load & {
          component: parameter.component
          value: {}
        }
        // apply workload to Kubernetes cluster
        apply: op.#Apply & {
          value: {
            component.value.workload
            metadata: name: parameter.component
            if parameter.serverIP!=_|_{
              // this data will override the env fields of the workload container
              spec: containers: [{env: [{name: "PrefixIP",value: parameter.serverIP}]}]
            }
          }
        }
        // wait until workload.status equal "Running"
        wait: op.#ConditionalWait & {
          continue: apply.value.status.phase =="Running"
        }