Knative Tutorials - Chapter 2 - Your first Knative application

	To run an application with Knative on a Kubernetes cluster and expose it to the public internet, you need:

	an application packaged as container image
	a Knative Service manifest file
	Service definition
	To expose an application on Knative, you need to define a Service object. (This is different than the Kubernetes Service type which helps you set up load balancing for Pods.)

	Save the following into a file named helloworld.yaml:



	helloworld.yaml
	apiVersion: serving.knative.dev/v1
	kind: Service
	metadata:
	name: hello
	spec:
	template:
	spec:
	containers:
	- image: gcr.io/knative-samples/helloworld-go
	ports:
	- containerPort: 8080
	env:
	- name: TARGET
	value: "World"


	This Knative Service example uses the container image gcr.io/knative-samples/helloworld-go, which is a Go web application listening on port 8080 (currently required port number by Knative).

	Deploy it:

	$ kubectl apply -f helloworld.yaml
	Verify it's deployed by querying "ksvc" (Knative Service) objects:

	$ kubectl get ksvc

	NAME CREATED AT
	helloworld 32s

	Make a request
	External requests to Knative applications in a cluster go through a single public load balancer called knative-ingressgateway which has a public IP address.

	Find the public IP address of the gateway (make a note of the EXTERNAL-IP field in the output), by running:

	$ kubectl get service --namespace=istio-system istio-ingressgateway
	Find the hostname of the application:

	$ kubectl get ksvc

	$ kubectl get ksvc helloworld --output jsonpath='{.status.domain}'
	The hostname of the application should be helloworld.default.example.com.

	Now, use curl to make the first request to this function (replace the IP_ADDRESS below with the gateway's external IP address you found earlier):

	$ curl -H "Host: helloworld.default.example.com" http://IP_ADDRESS
	$ curl -H "Host: hello.default.example.com" http://a9ae901051ac946dcb73928376469d03-1543302244.us-west-2.elb.amazonaws.com

	Hello world!
	After you made a request to the helloworld Service, you will see that a Pod is created on the Kubernetes cluster to serve the request. Query the list of Pods deployed:

	$ kubectl get pods

	NAME READY STATUS AGE
	helloworld-00001-deployment-58b8b4d79b 3/3 Running 1m


	Observe autoscaling

	Watch the pods and see how they scale to zero after traffic stops going to the URL:

	kubectl get pod -l serving.knative.dev/service=hello -w
	Note

	It may take up to 2 minutes for your pods to scale down. Pinging your service again resets this timer.

	Expected output

	NAME READY STATUS
	hello-world 2/2 Running
	hello-world 2/2 Terminating
	hello-world 1/2 Terminating
	hello-world 0/2 Terminating
	Scale up your Knative Service¶
	Rerun the Knative Service in your browser. You can see a new pod running again:

	Expected output

	NAME READY STATUS
	hello-world 0/2 Pending
	hello-world 0/2 ContainerCreating
	hello-world 1/2 Running
	hello-world 2/2 Running
	List your Knative Service
	View a list of Knative Services by running the command:

	$ kubectl get ksvc

	Introduction to Knative Serving API
	When you deploy the helloworld Service to Knative, it creates three kinds of objects: Configuration, Route, and Revision:

	kubectl get configuration,revision,route

	NAME CREATED AT
	configuration.serving.knative.dev/helloworld 28m
	NAME CREATED AT
	revision.serving.knative.dev/helloworld-00001 28m
	NAME CREATED AT
	route.serving.knative.dev/helloworld 28m
	Creating a new Revision
	Instead of TARGET=World, update the environment variable TARGET on your Knative Service to greet "Knative" instead.

	Edit your existing hello.yaml file to contain the following:

	apiVersion: serving.knative.dev/v1
	kind: Service
	metadata:
	name: hello
	spec:
	template:
	spec:
	containers:
	- image: gcr.io/knative-samples/helloworld-go
	ports:
	- containerPort: 8080
	env:
	- name: TARGET
	value: "Knative"


	Deploy the updated version of your Knative Service by running the command:

	$ kubectl apply -f hello.yaml



	Because you are updating an existing Knative Service, the URL won't change, but the new Revision has the new name hello-00002.

	Accessing the new Revision & View Existing Revisions

	To see the change, access the Knative Service again on your browser or use curl in your terminal:


	$ echo "Accessing URL $(kn service describe hello -o url)"
	$ curl "$(kn service describe hello -o url)"

	$ kubectl get revisions

	$ kn revisions list



	When running the kn command, the relevant column is TRAFFIC. You can see that 100% of traffic is going to the latest Revision, hello-00002, which is on the row with the highest GENERATION. 0% of traffic is going to the Revision hello-00001.



	When you create a new Revision of a Knative Service, Knative defaults to directing 100% of traffic to this latest Revision. You can change this default behavior by specifying how much traffic you want each Revision to receive.

	Splitting traffic between Revisions
	Split the traffic between the two Revisions:

	Add the traffic section to the bottom of your existing hello.yaml file

	apiVersion: serving.knative.dev/v1
	kind: Service
	metadata:
	name: hello
	spec:
	template:
	spec:
	containers:
	- image: gcr.io/knative-samples/helloworld-go
	ports:
	- containerPort: 8080
	env:
	- name: TARGET
	value: "Knative"
	traffic:
	- latestRevision: true
	percent: 50
	- latestRevision: false
	percent: 50
	revisionName: hello-00001


	Verify the traffic split
	$ kn revisions list
	$ kubectl get revisions

view raw gistfile1.txt hosted with

by GitHub

Here’s what each of these Serving APIs do:

`Service`	Describes an application on Knative.
`Revision`	Read-only snapshot of an application’s image and other settings (created by `Configuration`).
`Configuration`	Created by Service (from its `spec.configuration` field). It creates a new `Revision` when the `revisionTemplate` field changes.
`Route`	Configures how the traffic coming to the Service should be split between `Revision`s.

This diagram explains the relationship between them:

Rajesh Kumar

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