Getting Started with App Deployment

This guide shows you how to deploy an app using Knative, then interact with it using cURL requests.

Before you begin

You need:

  • A Kubernetes cluster with Knative Serving installed.
  • An image of the app that you’d like to deploy available on a container registry. The image of the sample app used in this guide is available on Google Container Registry.

Sample application

This guide demonstrates the basic workflow for deploying the Hello World sample app (Go) from the Google Container Registry. You can use these steps as a guide for deploying your container images from other registries like Docker Hub.

To deploy a local container image, you need to disable image tag resolution by running the following command:

# Set to dev.local/local-image when deploying local container images
docker tag local-image dev.local/local-image

Learn more about image tag resolution.

The Hello World sample app reads in an env variable, TARGET, then prints “Hello World: ${TARGET}!”. If TARGET isn’t defined, it will print “NOT SPECIFIED”.

Creating your Deployment with the Knative CLI

The easiest way to deploy a Knative Service is by using the Knative CLI kn.

Prerequisite: Install the kn binary as described in Installing the Knative CLI

It will create a corresponding resource description internally as when using a YAML file directly. kn provides a command-line mechanism for managing Services. It allows you to configure every aspect of a Service. The only mandatory flag for creating a Service is --image with the container image reference as value.

To create a Service directly at the cluster, use:

# Create a Knative service with the Knative CLI kn
kn service create helloworld-go --image gcr.io/knative-samples/helloworld-go --env TARGET="Go Sample v1"

If you want to deploy the sample app, leave the --image config as-is. If you’re deploying an image of your app, update the name of the Service and the value of the --image flag accordingly.

Now that you have deployed the service, Knative will perform the following steps:

  • Create a new immutable revision for this version of the app.
  • Perform network programming to create a route, ingress, service, and load balancer for your app.
  • Automatically scale your pods up and down based on traffic, including to zero active pods.

Creating your Deployment with YAML

Alternatively, to deploy an app using Knative, you can also create the configuration in a YAML file that defines a service. For more information about the Service object, see the Resource Types documentation.

This configuration file specifies metadata about the application, points to the hosted image of the app for deployment, and allows the deployment to be configured. For more information about what configuration options are available, see the Serving spec documentation.

To create the same application as in the previous kn example, create a new file named service.yaml, then copy and paste the following content into it:

apiVersion: serving.knative.dev/v1 # Current version of Knative
kind: Service
metadata:
  name: helloworld-go # The name of the app
  namespace: default # The namespace the app will use
spec:
  template:
    spec:
      containers:
        - image: gcr.io/knative-samples/helloworld-go # Reference to the image of the app
          env:
            - name: TARGET # The environment variable printed out by the sample app
              value: "Go Sample v1"

If you want to deploy the sample app, leave the config file as-is. If you’re deploying an image of your app, update the name of the Service (.metadata.name) and the reference to the container image (.spec.containers[].image) accordingly.

From the directory where the new service.yaml file was created, apply the configuration:

kubectl apply --filename service.yaml

Now that you have deployed the service, Knative will perform the following steps:

  • Create a new immutable revision for this version of the app.
  • Perform network programming to create a route, ingress, service, and load balancer for your app.
  • Automatically scale your pods up and down based on traffic, including to zero active pods.

Interacting with your app

To see if your app has been deployed successfully, you need the URL created by Knative.

  1. To find the URL for your service, use either kn or kubectl
kn service describe helloworld-go

This will return something like

Name        helloworld-go
Namespace   default
Age         12m
URL         http://helloworld-go.default.34.83.80.117.xip.io

Revisions:
  100%  @latest (helloworld-go-dyqsj-1) [1] (39s)
        Image:  gcr.io/knative-samples/helloworld-go (pinned to 946b7c)

Conditions:
  OK TYPE                   AGE REASON
  ++ Ready                  25s
  ++ ConfigurationsReady    26s
  ++ RoutesReady            25s

kubectl get ksvc helloworld-go

The command will return the following:

NAME            URL                                                LATESTCREATED         LATESTREADY           READY   REASON
helloworld-go   http://helloworld-go.default.34.83.80.117.xip.io   helloworld-go-96dtk   helloworld-go-96dtk   True

Note: If your URL includes example.com then consult the setup instructions for configuring DNS (e.g. with xip.io), or using a Custom Domain.

If you changed the name from helloworld-go to something else when creating the .yaml file, replace helloworld-go in the above commands with the name you entered.

  1. Now you can make a request to your app and see the results. Replace the URL with the one returned by the command in the previous step.

    # curl http://helloworld-go.default.34.83.80.117.xip.io
Hello World: Go Sample v1!

    If you deployed your app, you might want to customize this cURL request to interact with your application.

    It can take a few seconds for Knative to scale up your application and return a response.

    Note: Add -v option to get more detail if the curl command failed.

You’ve successfully deployed your first application using Knative!

Cleaning up

To remove the sample app from your cluster, delete the service record:

kn service delete helloworld-go

Alternatively, you can also delete the service with kubectl via the definition file or by name.

# Delete with the KService given in the yaml file:
kubectl delete --filename service.yaml

# Or just delete it by name:
kubectl delete kservice helloworld-go