View on GitHub

Knative Hands-on Workshop

Why is deploying a Knative service easier than a Kubernetess deployment?

Knative Revisions

A Knative Revision is a specific version of a code deployment.

If you deploy a new version of an app in Kubernetes, you typically change the deployment.yaml file and apply the changed version using kubectl. Kubernetes will then perform a rolling update from the old to the new version.

If you have used Istio before, you know that with Istio you can deploy multiple versions of your application.

With Knative, every deployment of a new version will create a new revision. If you explicitly name the revisions, you will have to change the name with every new deployment, otherwise Knative will decline the deployment.

This is version 2 of the helloworld app, specified in service-v2.yaml:

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: helloworld
spec:
  template:
    metadata:
      name: helloworld-v2
    spec:
      containers:
        - image: docker.io/ibmcom/kn-helloworld
          env:
            - name: TARGET
              value: "HelloWorld Sample v2 -- UPDATED"

Version 2 has a new value for the TARGET environment variable. It also has a new revision name (‘helloworld-v2’), if this does not change, Knative will deny the request.

Apply the new version:
```
kubectl apply -f service-v2.yaml
```

Check the Knative Service:

kn service describe helloworld

Output:

Name:       helloworld
Namespace:  default
Age:        53s
URL:        http://helloworld....appdomain.cloud

Revisions:  
  100%  @latest (helloworld-v2) [2] (44s)
        Image:  docker.io/ibmcom/kn-helloworld (at b17fc9)
  
Conditions:  
  OK TYPE                   AGE REASON
  ++ Ready                  40s 
  ++ ConfigurationsReady    40s 
  ++ RoutesReady            40s 

You can see that the ‘@latest’ revison is ‘helloworld-v2’.

Test it with curl, output:
```
Hello HelloWorld Sample v2 -- UPDATED!
```
Display the Revisions:
```
kn revision list
```
Output:
```
NAME            SERVICE      GENERATION   AGE   CONDITIONS   READY   REASON
helloworld-v2   helloworld   2            12m   3 OK / 4     True    
helloworld-v1   helloworld   1            12m   3 OK / 4     True    
```
As you can see, both revisions are there but in the description of the Knative Service above you can see that only Revision 2 is currently used.

So how is this different from a typical Kubernetes rolling update? The difference is that both revisions are available and we will see in the next section how to make use of that.

Continue with the next part Knative Traffic Management