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kn service commands

Creating serverless applications by using the Knative CLI

Using the Knative (kn) CLI to create serverless applications provides a more streamlined and intuitive user interface over modifying YAML files directly. You can use the kn service create command to create a basic serverless application.

Prerequisites

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

  • You have installed the Knative (kn) CLI.

  • You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

Procedure

  • Create a Knative service:

    $ kn service create <service-name> --image <image> --tag <tag-value>

    Where:

    • --image is the URI of the image for the application.

    • --tag is an optional flag that can be used to add a tag to the initial revision that is created with the service.

      Example command
      $ kn service create showcase \
    --image quay.io/openshift-knative/showcase
      Example output
      Creating service 'showcase' in namespace 'default':

  0.271s The Route is still working to reflect the latest desired specification.
  0.580s Configuration "showcase" is waiting for a Revision to become ready.
  3.857s ...
  3.861s Ingress has not yet been reconciled.
  4.270s Ready to serve.

Service 'showcase' created with latest revision 'showcase-00001' and URL:
http://showcase-default.apps-crc.testing

Updating serverless applications by using the Knative CLI

You can use the kn service update command for interactive sessions on the command line as you build up a service incrementally. In contrast to the kn service apply command, when using the kn service update command you only have to specify the changes that you want to update, rather than the full configuration for the Knative service.

Example commands

  • Update a service by adding a new environment variable:

    $ kn service update <service_name> --env <key>=<value>

  • Update a service by adding a new port:

    $ kn service update <service_name> --port 80

  • Update a service by adding new request and limit parameters:

    $ kn service update <service_name> --request cpu=500m --limit memory=1024Mi --limit cpu=1000m

  • Assign the latest tag to a revision:

    $ kn service update <service_name> --tag <revision_name>=latest

  • Update a tag from testing to staging for the latest READY revision of a service:

    $ kn service update <service_name> --untag testing --tag @latest=staging

  • Add the test tag to a revision that receives 10% of traffic, and send the rest of the traffic to the latest READY revision of a service:

    $ kn service update <service_name> --tag <revision_name>=test --traffic test=10,@latest=90

Applying service declarations

You can declaratively configure a Knative service by using the kn service apply command. If the service does not exist it is created, otherwise the existing service is updated with the options that have been changed.

The kn service apply command is especially useful for shell scripts or in a continuous integration pipeline, where users typically want to fully specify the state of the service in a single command to declare the target state.

When using kn service apply you must provide the full configuration for the Knative service. This is different from the kn service update command, which only requires you to specify in the command the options that you want to update.

Example commands

  • Create a service:

    $ kn service apply <service_name> --image <image>

  • Add an environment variable to a service:

    $ kn service apply <service_name> --image <image> --env <key>=<value>

  • Read the service declaration from a JSON or YAML file:

    $ kn service apply <service_name> -f <filename>

Describing serverless applications by using the Knative CLI

You can describe a Knative service by using the kn service describe command.

Example commands

  • Describe a service:

    $ kn service describe --verbose <service_name>

    The --verbose flag is optional but can be included to provide a more detailed description. The difference between a regular and verbose output is shown in the following examples:

    Example output without --verbose flag
    Name:       showcase
Namespace:  default
Age:        2m
URL:        http://showcase-default.apps.ocp.example.com

Revisions:
  100%  @latest (showcase-00001) [1] (2m)
        Image:  quay.io/openshift-knative/showcase (pinned to aaea76)

Conditions:
  OK TYPE                   AGE REASON
  ++ Ready                   1m
  ++ ConfigurationsReady     1m
  ++ RoutesReady             1m
    Example output with --verbose flag
    Name:         showcase
Namespace:    default
Annotations:  serving.knative.dev/creator=system:admin
              serving.knative.dev/lastModifier=system:admin
Age:          3m
URL:          http://showcase-default.apps.ocp.example.com
Cluster:      http://showcase.default.svc.cluster.local

Revisions:
  100%  @latest (showcase-00001) [1] (3m)
        Image:  quay.io/openshift-knative/showcase (pinned to aaea76)
        Env:    GREET=Bonjour

Conditions:
  OK TYPE                   AGE REASON
  ++ Ready                   3m
  ++ ConfigurationsReady     3m
  ++ RoutesReady             3m

  • Describe a service in YAML format:

    $ kn service describe <service_name> -o yaml

  • Describe a service in JSON format:

    $ kn service describe <service_name> -o json

  • Print the service URL only:

    $ kn service describe <service_name> -o url