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Version: v1.4

If Conditions

This section introduces how to add if conditions to workflow steps.

In the KubeVela workflow, each step can specify an if, in which you can determine whether the step should be executed.

No If specified

In the case where a step does not specify an If, KubeVela will determine whether to execute the step based on the status of the previous steps. In default, if all the previous steps are succeeded, the step will be executed.

This also means that if step A fails, step B after step A will be skipped and will not be executed.

Apply the following example:

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
name: err-with-no-if
namespace: default
spec:
components:
- name: express-server
type: webservice
properties:
image: oamdev/hello-world
ports:
- port: 8000
workflow:
steps:
- name: apply-err
type: apply-object
properties:
value:
test: err
- name: apply-comp
type: apply-component
properties:
component: express-server

Use vela status to check the status of the Application:

$ vela status err-with-no-if
About:

Name: err-with-no-if
Namespace: default
Created at: 2022-06-24 18:14:46 +0800 CST
Status: workflowTerminated

Workflow:

mode: StepByStep
finished: true
Suspend: false
Terminated: true
Steps
- id:bztlmifsjl
name:apply-err
type:apply-object
phase:failed
message:step apply: run step(provider=kube,do=apply): Object 'Kind' is missing in '{"test":"err"}'
- id:el8quwh8jh
name:apply-comp
type:apply-component
phase:skipped
message:

Services:

As you can see, the step apply-err will fail due to an attempt to deploy an invalid resource, and the step apply-comp will be skipped because the previous step failed.

If Always

If you want a step to be executed anyway, you can specify if to always for this step.

Apply the following example:

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
name: err-with-always
namespace: default
spec:
components:
- name: invalid
type: webservice
properties:
image: invalid
ports:
- port: 8000
workflow:
steps:
- name: comp
type: apply-component
timeout: 5s
outputs:
- name: status
valueFrom: output.status.conditions[0].type + output.status.conditions[0].status
properties:
component: invalid
- name: notification
type: notification
inputs:
- from: status
parameterKey: slack.message.text
if: always
properties:
slack:
url:
value: <your slack url>

Use vela status to check the status of the Application:

$ vela status err-with-always
About:

Name: err-with-always
Namespace: default
Created at: 2022-06-27 17:30:29 +0800 CST
Status: workflowTerminated

Workflow:

mode: StepByStep
finished: true
Suspend: false
Terminated: true
Steps
- id:loeqr6dlcn
name:comp
type:apply-component
phase:failed
message:
- id:hul9tayu82
name:notification
type:notification
phase:succeeded
message:

Services:

- Name: invalid
Cluster: local Namespace: default
Type: webservice
Unhealthy Ready:0/1
No trait applied

You can see that step comp will try to deploy a component whose image is invalid, and the component will fail due to timeout after five seconds because the image cannot be pulled. In the meanwhile, this step passes the component's status as outputs. The step notification will be executed because if: always is specified. At the same time, the content of the message notification is the status of the component in the previous step. Therefore, we can see the message notification carrying the status information in slack.

Custom If conditions

Note: You need to upgrade to version 1.5 or above to use custom If conditions.

You can also write your own judgment logic to determine whether the step should be executed. Note: The value in if will be executed as CUE codes. KubeVela provides some built-in variables in if, they are:

  • statusstatus contains status information for all workflow steps. You can use status.<step-name>.phase == "succeeded" to determine the status of a step, or you can use the simplified status.<step-name>.succeeded to determine.
  • inputsinputs contains all the inputs parameters of the step. You can use inputs.<input-name> == "value" to get input for the step.

Note that if your step name or inputs name is not a valid CUE variable name (eg: contains -, or starts with a number, etc.), you can refer to it as follows: status["invalid-name"].failed

Apply the following example:

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
name: custom-if
namespace: default
spec:
components:
- name: comp-custom-if
type: webservice
properties:
image: crccheck/hello-world
port: 8000
traits:
workflow:
steps:
- name: apply
type: apply-component
properties:
component: comp-custom-if
outputs:
- name: comp-output
valueFrom: context.name
- name: notification
type: notification
inputs:
- from: comp-output
parameterKey: slack.message.text
if: inputs["comp-output"] == "custom-if"
properties:
slack:
url:
value: <your slack url>
- name: notification-skip
type: notification
if: status.notification.failed
properties:
slack:
url:
value: <your slack url>
message:
text: this notification should be skipped
- name: notification-succeeded
type: notification
if: status.notification.succeeded
properties:
slack:
url:
value: <your slack url>
message:
text: the notification is succeeded

Use vela status to check the status of the Application:

$ vela status custom-if
About:

Name: custom-if
Namespace: default
Created at: 2022-06-25 00:37:14 +0800 CST
Status: running

Workflow:

mode: StepByStep
finished: true
Suspend: false
Terminated: false
Steps
- id:un1zd8qc6h
name:apply
type:apply-component
phase:succeeded
message:
- id:n5xbtgsi68
name:notification
type:notification
phase:succeeded
message:
- id:2ufd3v6n78
name:notification-skip
type:notification
phase:skipped
message:
- id:h644x6o8mb
name:notification-succeeded
type:notification
phase:succeeded
message:

Services:

- Name: comp-custom-if
Cluster: local Namespace: default
Type: webservice
Healthy Ready:1/1
No trait applied

As you can see, after the first step apply succeeded, the outputs comp-output will be output. The second step notification refers to the outputs of the first step as inputs and makes a judgment. After the condition is met, the notification is successfully sent. The third step notification-skip judges whether the second step is in a failed state. If the condition is not met, this step is skipped. The fourth step notification-succeeded judges whether the second step is successful, if the condition is met, the step is successfully executed.