Serverless applications using Knative services

To deploy a serverless application using OpenShift Serverless, you must create a Knative service. Knative services are Kubernetes services, defined by a route and a configuration, and contained in a YAML file.

Example Knative service YAML
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: hello (1)
  namespace: default (2)
spec:
  template:
    spec:
      containers:
        - image: docker.io/openshift/hello-openshift (3)
          env:
            - name: RESPONSE (4)
              value: "Hello Serverless!"
1 The name of the application.
2 The namespace the application will use.
3 The image of the application.
4 The environment variable printed out by the sample application.

You can create a serverless application by using one of the following methods:

  • Create a Knative service from the OpenShift Container Platform web console.

  • Create a Knative service using the kn CLI.

  • Create and apply a YAML file.

Creating serverless applications using the OpenShift Container Platform web console

You can create a serverless application using either the Developer or Administrator perspective in the OpenShift Container Platform web console.

Creating serverless applications using the Administrator perspective

Prerequisites

To create serverless applications using the Administrator perspective, ensure that you have completed the following steps.

  • The OpenShift Serverless Operator and Knative Serving are installed.

  • You have logged in to the web console and are in the Administrator perspective.

Procedure
  1. Navigate to the ServerlessServices page.

    Services page
  2. Click Create Service.

  3. Manually enter YAML or JSON definitions, or by dragging and dropping a file into the editor.

    Text editor
  4. Click Create.

Creating serverless applications using the Developer perspective

For more information about creating applications using the Developer perspective in OpenShift Container Platform, see the documentation on Creating applications using the Developer perspective.

Creating serverless applications using the kn CLI

The following procedure describes how you can create a basic serverless application using the kn CLI.

Prerequisites
  • OpenShift Serverless Operator and Knative Serving are installed on your cluster.

  • You have installed kn CLI.

Procedure
  1. Create the Knative service by entering the following command:

    $ kn service create <service-name> --image <image> --env <key=value>
    Example command
    $ kn service create hello --image docker.io/openshift/hello-openshift --env RESPONSE="Hello Serverless!"
    Example output
    Creating service 'hello' in namespace 'default':
    
      0.271s The Route is still working to reflect the latest desired specification.
      0.580s Configuration "hello" is waiting for a Revision to become ready.
      3.857s ...
      3.861s Ingress has not yet been reconciled.
      4.270s Ready to serve.
    
    Service 'hello' created with latest revision 'hello-bxshg-1' and URL:
    http://hello-default.apps-crc.testing

Creating serverless applications using YAML

To create a serverless application, you can create a YAML file and apply it using oc apply.

You can create a YAML file by copying the following example:

Example Knative service YAML
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: hello
  namespace: default
spec:
  template:
    spec:
      containers:
        - image: docker.io/openshift/hello-openshift
          env:
            - name: RESPONSE
              value: "Hello Serverless!"

In this example, the YAML file is named hello-service.yaml.

Procedure
  1. Navigate to the directory where the hello-service.yaml file is contained, and deploy the application by applying the YAML file:

    $ oc apply --filename hello-service.yaml

After the service has been created and the application has been deployed, Knative will create a new immutable revision for this version of the application.

Knative will also perform network programming to create a route, ingress, service, and load balancer for your application, and will automatically scale your pods up and down based on traffic, including inactive Pods.

Verifying your serverless application deployment

To verify that your serverless application has been deployed successfully, you must get the application URL created by Knative, and then send a request to that URL and observe the output.

OpenShift Serverless supports the use of both HTTP and HTTPS URLs, however the output from oc get ksvc <SERVICE-NAME> will always print URLs using the http:// format.

Procedure
  1. Find the application URL by entering:

    $ oc get ksvc hello
    Example output
    NAME            URL                                        LATESTCREATED         LATESTREADY           READY   REASON
    hello   http://hello-default.example.com   hello-4wsd2   hello-4wsd2   True
  2. Make a request to your cluster and observe the output.

    Example HTTP request
    $ curl http://hello-default.example.com
    Hello Serverless!
    Example HTTPS request
    $ curl https://hello-default.example.com
    Hello Serverless!
  3. Optional. If you receive an error relating to a self-signed certificate in the certificate chain, you can add the --insecure flag to the curl command to ignore the error.

    Self-signed certificates must not be used in a production deployment. This method is only for testing purposes.

    Example
    $ curl https://hello-default.example.com --insecure
    Hello Serverless!
  4. Optional. If your OpenShift Container Platform cluster is configured with a certificate that is signed by a certificate authority (CA) but not yet globally configured for your system, you can specify this with the curl command. The path to the certificate can be passed to the curl command by using the --cacert flag.

    Example
    $ curl https://hello-default.example.com --cacert <file>
    Hello Serverless!

Interacting with a serverless application using HTTP2 / gRPC

OpenShift Container Platform routes do not support HTTP2, and therefore do not support gRPC as this is transported by HTTP2. If you use these protocols in your application, you must call the application using the ingress gateway directly. To do this you must find the ingress gateway’s public address and the application’s specific host.

Procedure
  1. Find the application host. See the instructions in Verifying your serverless application deployment.

  2. The ingress gateway’s public address can be determined using this command:

    $ oc -n knative-serving-ingress get svc kourier

    The output will be similar to this example:

    NAME                   TYPE           CLUSTER-IP      EXTERNAL-IP                                                             PORT(S)                                                                                                                                      AGE
    kourier   LoadBalancer   172.30.51.103   a83e86291bcdd11e993af02b7a65e514-33544245.us-east-1.elb.amazonaws.com   80:31380/TCP,443:31390/TCP   67m

    The public address is surfaced in the EXTERNAL-IP field, and in this case would be:

    a83e86291bcdd11e993af02b7a65e514-33544245.us-east-1.elb.amazonaws.com
  3. Manually set the host header of your HTTP request to the application’s host, but direct the request itself against the public address of the ingress gateway.

    Here is an example, using the information obtained from the steps in Verifying your serverless application deployment:

    $ curl -H "Host: hello-default.example.com" a83e86291bcdd11e993af02b7a65e514-33544245.us-east-1.elb.amazonaws.com
    Hello Serverless!

    You can also make a gRPC request by setting the authority to the application’s host, while directing the request against the ingress gateway directly.

    Here is an example of what that looks like in the Golang gRPC client:

    Ensure that you append the respective port (80 by default) to both hosts as shown in the example.

    grpc.Dial(
        "a83e86291bcdd11e993af02b7a65e514-33544245.us-east-1.elb.amazonaws.com:80",
        grpc.WithAuthority("hello-default.example.com:80"),
        grpc.WithInsecure(),
    )