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Version: v1.5

Component Orchestration

This section will introduce the dependencies in components and how to pass data between components.

We use helm in the examples, make sure you enable the fluxcd addon:

vela addon enable fluxcd

Dependency

We can use dependsOn to specify the dependencies between components.

For example, component A depends on component B:

...
components:
- name: A
type: helm
dependsOn:
- B
- name: B
type: helm

In this case, KubeVela will deploy B first, and then deploy A when the component B is running.

How to use

If we want to apply a MySQL cluster, we need:

  1. Apply a secret for MySQL password.
  2. Apply MySQL controller.
  3. Apply MySQL cluster.

Apply the following file:

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
name: mysql
namespace: default
spec:
components:
- name: mysql-secret
type: raw
properties:
apiVersion: v1
kind: Secret
metadata:
name: mysql-secret
type: kubernetes.io/opaque
stringData:
ROOT_PASSWORD: test
- name: mysql-controller
type: helm
properties:
repoType: helm
url: https://presslabs.github.io/charts
chart: mysql-operator
version: "0.4.0"
- name: mysql-cluster
type: raw
dependsOn:
- mysql-controller
- mysql-secret
properties:
apiVersion: mysql.presslabs.org/v1alpha1
kind: MysqlCluster
metadata:
name: mysql-cluster
spec:
replicas: 1
secretName: mysql-secret

Expected Outcome

Check the application in the cluster:

$ vela ls
APP COMPONENT TYPE TRAITS PHASE HEALTHY STATUS CREATED-TIME
mysql mysql-secret raw runningWorkflow 2021-10-14 12:09:55 +0800 CST
├─ mysql-controller helm runningWorkflow 2021-10-14 12:09:55 +0800 CST
└─ mysql-cluster raw runningWorkflow 2021-10-14 12:09:55 +0800 CST

In the beginning, the status is running workflow since the mysql-controller is not ready.

$ vela ls
APP COMPONENT TYPE TRAITS PHASE HEALTHY STATUS CREATED-TIME
mysql mysql-secret raw running healthy 2021-10-14 12:09:55 +0800 CST
├─ mysql-controller helm running healthy 2021-10-14 12:09:55 +0800 CST
└─ mysql-cluster raw running 2021-10-14 12:09:55 +0800 CST

After a while, all components is running successfully. The mysql-cluster will be deployed after mysql-controller and mysql-secret is healthy.

dependsOn use healthy to check status. If the component is healthy, then KubeVela will deploy the next component. If you want to customize the healthy status of the component, please refer to Status Write Back

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
  1. 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
valueFrom: 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

Check the application in the cluster:

$ vela ls

APP COMPONENT TYPE TRAITS PHASE HEALTHY STATUS CREATED-TIME
wordpress-with-mysql mysql helm running healthy 2021-10-12 18:04:10 +0800 CST
└─ wordpress helm running healthy 2021-10-12 18:04:10 +0800 CST

The WordPress with MySQL has been successfully applied.