kubevela.github.io/docs/core-concepts/application.md

title
The Application Model

KubeVela introduces Open Application Model (OAM) to capture a full deployment of micro-services application across hybrid environments.

The Application Deployment Plan

With this model, a typical deployment plan in KubeVela looks as below:

# sample.yaml
apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
  name: website
spec:
  components:
    - name: frontend              # e.g. we want to deploy a frontend component and serves as web service
      type: webservice
      properties:
        image: nginx
      traits:
        - type: cpuscaler         # e.g. we add a CPU based auto scaler to this component
          properties:
            min: 1
            max: 10
            cpuPercent: 60
        - type: sidecar           # add a sidecar container into this component
          properties:
            name: "sidecar-test"
            image: "fluentd"
    - name: backend
      type: worker
      properties:
        image: busybox
        cmd:
          - sleep
          - '1000'
  policies:
    - name: demo-policy
      type: env-binding
      properties:
        envs:
          - name: test
            placement:
              clusterSelector:
                name: cluster-test
          - name: prod
            placement:
              clusterSelector:
                name: cluster-prod
  workflow:
    steps:
      #workflow step name
      - name: deploy-test-env
        type: deploy2env
        properties:
          # Specify the policy name
          policy: demo-policy
          # Specify the env name in the policy
          env: test    
      - name: manual-approval
        # use suspend can stop workflow and wait here until condition changed
        type: suspend
      - name: deploy-prod-env
        type: deploy2env
        properties:
          # Specify the policy name
          policy: demo-policy
          # Specify the env name in the policy
          env: prod    

The building blocks in this entity are explained as below.

Components

An application could be composed by multiple components. KubeVela already built-in with several widely used components definitions to help you model an application deployment, you can list them by using KubeVela CLI:

vela components 

The output shows:

NAME          NAMESPACE   WORKLOAD                              DESCRIPTION
helm          vela-system autodetects.core.oam.dev              helm release is a group of K8s resources from either git
                                                                repository or helm repo
kustomize     vela-system autodetects.core.oam.dev              kustomize can fetching, building, updating and applying
                                                                Kustomize manifests from git repo.
task          vela-system jobs.batch                            Describes jobs that run code or a script to completion.
webservice    vela-system deployments.apps                      Describes long-running, scalable, containerized services
                                                                that have a stable network endpoint to receive external
                                                                network traffic from customers.
worker        vela-system deployments.apps                      Describes long-running, scalable, containerized services
                                                                that running at backend. They do NOT have network endpoint
                                                                to receive external network traffic.                    
alibaba-ack   vela-system configurations.terraform.core.oam.dev Terraform configuration for Alibaba Cloud ACK cluster
alibaba-oss   vela-system configurations.terraform.core.oam.dev Terraform configuration for Alibaba Cloud OSS object
alibaba-rds   vela-system configurations.terraform.core.oam.dev Terraform configuration for Alibaba Cloud RDS object

Traits

Traits are operational behaviors that you can attach to component. KubeVela also has built-in traits installed, search them by using KubeVela CLI:

vela traits 

The result can be:

NAME        NAMESPACE   APPLIES-TO        CONFLICTS-WITH  POD-DISRUPTIVE  DESCRIPTION                                          
annotations vela-system deployments.apps                  true            Add annotations for your Workload.                   
cpuscaler   vela-system webservice,worker                 false           Automatically scale the component based on CPU usage.
ingress     vela-system webservice,worker                 false           Enable public web traffic for the component.         
labels      vela-system deployments.apps                  true            Add labels for your Workload.                        
scaler      vela-system webservice,worker                 false           Manually scale the component.                        
sidecar     vela-system deployments.apps                  true            Inject a sidecar container to the component.   

Policy

Policy enforces deployment process of the application, such as quality gates, security groups, placement strategy, fire walls, SLO targets and so on.

Workflow

Workflow allows you to assemble components, operation and task steps into a DAG, and it is process-oriented. Typical workflow steps includes pause, manual verification, waiting state, data flow transmission, multi-environment rollout, and A/B testing, etc.

Each policy and workflow step is a independent capability entity that is fully plugable, KubeVela allows you to create your own step through CUE.

What's Next

Here are some recommended next steps:

• Start using KubeVela from deploying Helm component.
• Learn about customizing this application model in programmable approach.