kubevela.github.io/versioned_docs/version-v1.0/developers/extensions/set-rollout.md

title
Setting Rollout Strategy

Note: rollout is one of the extension capabilities installed from cap center, please install it if you can't find it in vela traits.

The rollout section is used to configure Canary strategy to release your app.

Add rollout config under express-server along with a route.

name: testapp
services:
  express-server:
    type: webservice
    image: oamdev/testapp:rolling01
    port: 80

    rollout:
      replicas: 5
      stepWeight: 20
      interval: "30s"
    
    route:
      domain: "example.com"

The full specification of rollout could show up by $ vela show rollout or be found on its reference documentation

Apply this appfile.yaml:

$ vela up

You could check the status by:

$ vela status testapp
About:

  Name:      	testapp
  Namespace: 	myenv
  Created at:	2020-11-09 17:34:38.064006 +0800 CST
  Updated at:	2020-11-10 17:05:53.903168 +0800 CST

Services:

  - Name: testapp
    Type: webservice
    HEALTHY Ready: 5/5
    Traits:
      - ✅ rollout: interval=5s
		replicas=5
		stepWeight=20
      - ✅ route: 	Visiting URL: http://example.com	IP: <your-ingress-IP-address>

    Last Deployment:
      Created at: 2020-11-09 17:34:38 +0800 CST
      Updated at: 2020-11-10T17:05:53+08:00

Visiting this app by:

$ curl -H "Host:example.com" http://<your-ingress-IP-address>/
Hello World -- Rolling 01

In day 2, assuming we have make some changes on our app and build the new image and name it by oamdev/testapp:v2.

Let's update the appfile by:

name: testapp
services:
  express-server:
    type: webservice
-   image: oamdev/testapp:rolling01
+   image: oamdev/testapp:rolling02
    port: 80
    rollout:
      replicas: 5
      stepWeight: 20
      interval: "30s"
    route:
      domain: example.com

Apply this appfile.yaml again:

$ vela up

You could run vela status several times to see the instance rolling:

$ vela status testapp
About:

  Name:      	testapp
  Namespace: 	myenv
  Created at:	2020-11-12 19:02:40.353693 +0800 CST
  Updated at:	2020-11-12 19:02:40.353693 +0800 CST

Services:

  - Name: express-server
    Type: webservice
    HEALTHY express-server-v2:Ready: 1/1 express-server-v1:Ready: 4/4
    Traits:
      - ✅ rollout: interval=30s
		replicas=5
		stepWeight=20
      - ✅ route: 	 Visiting by using 'vela port-forward testapp --route'

    Last Deployment:
      Created at: 2020-11-12 17:20:46 +0800 CST
      Updated at: 2020-11-12T19:02:40+08:00

You could then try to curl your app multiple times and and see how the app being rollout following Canary strategy:

$ curl -H "Host:example.com" http://<your-ingress-ip-address>/
Hello World -- This is rolling 02                                        
$ curl -H "Host:example.com" http://<your-ingress-ip-address>/
Hello World -- Rolling 01                                                                
$ curl -H "Host:example.com" http://<your-ingress-ip-address>/
Hello World -- Rolling 01                                                    
$ curl -H "Host:example.com" http://<your-ingress-ip-address>/
Hello World -- This is rolling 02                                         
$ curl -H "Host:example.com" http://<your-ingress-ip-address>/
Hello World -- Rolling 01                                                  
$ curl -H "Host:example.com" http://<your-ingress-ip-address>/
Hello World -- This is rolling 02

How Rollout works?

Rollout trait implements progressive release process to rollout your app following Canary strategy.

In detail, Rollout controller will create a canary of your app , and then gradually shift traffic to the canary while measuring key performance indicators like HTTP requests success rate at the same time.

In this sample, for every 10s, 5% traffic will be shifted to canary from the primary, until the traffic on canary reached 50%. At the mean time, the instance number of canary will automatically scale to replicas: 2 per configured in Appfile.

Based on analysis result of the KPIs during this traffic shifting, a canary will be promoted or aborted if analysis is failed. If promoting, the primary will be upgraded from v1 to v2, and traffic will be fully shifted back to the primary instances. So as result, canary instances will be deleted after the promotion finished.

Note: KubeVela's Rollout trait is implemented with Weaveworks Flagger operator.