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Getting started with functions - Functions | Serverless | OpenShift Container Platform 4.7
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Getting started with functions

Function lifecycle management includes creating, building, and deploying a function. Optionally, you can also test a deployed function by invoking it. You can do all of these operations on OpenShift Serverless using the kn func tool.

OpenShift Serverless Functions is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview/.

Prerequisites

Before you can complete the following procedures, you must ensure that you have completed all of the prerequisite tasks in Setting up OpenShift Serverless Functions.

Creating functions

Before you can build and deploy a function, you must create it by using the Knative (kn) cli. You can specify the path, runtime, template, and image registry as flags on the command line, or use the -c flag to start the interactive experience in the terminal.

Prerequisites

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

  • You have installed the Knative (kn) cli.

Procedure

  • Create a function project:

    $ kn func create -r <repository> -l <runtime> -t <template> <path>

    • Accepted runtime values include node, go, python, quarkus, and typescript.

    • Accepted template values include http and events.

      Example command
      $ kn func create -l typescript -t events examplefunc
      Example output
      Project path:  /home/user/demo/examplefunc
Function name: examplefunc
Runtime:       typescript
Template:      events
Writing events to /home/user/demo/examplefunc

    • Alternatively, you can specify a repository that contains a custom template.

      Example command
      $ kn func create -r https://github.com/boson-project/templates/ -l node -t hello-world examplefunc
      Example output
      Project path:  /home/user/demo/examplefunc
Function name: examplefunc
Runtime:       node
Template:      hello-world
Writing events to /home/user/demo/examplefunc

Running a function locally

You can use the kn func run command to run a function locally in the current directory or in the directory specified by the --path flag. If the function that you are running has never previously been built, or if the project files have been modified since the last time it was built, the kn func run command builds the function before running it by default.

Example command to run a function in the current directory
$ kn func run
Example command to run a function in a directory specified as a path
$ kn func run --path=<directory_path>

You can also force a rebuild of an existing image before running the function, even if there have been no changes to the project files, by using the --build flag:

Example run command using the build flag
$ kn func run --build

If you set the build flag as false, this disables building of the image, and runs the function using the previously built image:

Example run command using the build flag
$ kn func run --build=false

You can use the help command to learn more about kn func run command options:

Build help command
$ kn func help run

Building functions

Before you can run a function, you must build the function project. If you are using the kn func run command, the function is built automatically. However, you can use the kn func build command to build a function without running it, which can be useful for advanced users or debugging scenarios.

The kn func build command creates an OCI container image that can be run locally on your computer or on an OpenShift Container Platform cluster. This command uses the function project name and the image registry name to construct a fully qualified image name for your function.

Image container types

By default, kn func build creates a container image by using Red Hat Source-to-Image (S2I) technology.

Example build command using Red Hat Source-to-Image (S2I)
$ kn func build

You can use CNCF Cloud Native Buildpacks technology instead, by adding the --builder flag to the command and specifying the pack strategy:

Example build command using CNCF Cloud Native Buildpacks
$ kn func build --builder pack

Image registry types

The OpenShift Container Registry is used by default as the image registry for storing function images.

Example build command using OpenShift Container Registry
$ kn func build
Example output
Building function image
Function image has been built, image: registry.redhat.io/example/example-function:latest

You can override using OpenShift Container Registry as the default image registry by using the --registry flag:

Example build command overriding OpenShift Container Registry to use quay.io
$ kn func build --registry quay.io/username
Example output
Building function image
Function image has been built, image: quay.io/username/example-function:latest

Push flag

You can add the --push flag to a kn func build command to automatically push the function image after it is successfully built:

Example build command using OpenShift Container Registry
$ kn func build --push

Help command

You can use the help command to learn more about kn func build command options:

Build help command
$ kn func help build

Building and deploying functions on the cluster

You can use the Knative (kn) cli to initiate a function project build and then deploy the function directly on the cluster. To build a function project in this way, the source code for your function project must exist in a Git repository branch that is accessible to your cluster.

OpenShift Serverless Functions is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview/.
Prerequisites

  • Red Hat OpenShift Pipelines must be installed on your cluster.

  • You have installed the OpenShift cli (oc).

  • You have installed the Knative (kn) cli.

Procedure

  1. In each namespace where you want to run Pipelines and deploy a function, you must create the following resources:

    1. Create the functions buildpacks Tekton task to be able to build the function image:

      $ oc apply -f https://raw.githubusercontent.com/openshift-knative/kn-plugin-func/serverless-1.22.0/pipelines/resources/tekton/task/func-buildpacks/0.1/func-buildpacks.yaml

    2. Create the kn func deploy Tekton task to be able to deploy the function in the pipeline:

      $ oc apply -f https://raw.githubusercontent.com/openshift-knative/kn-plugin-func/serverless-1.22.0/pipelines/resources/tekton/task/func-deploy/0.1/func-deploy.yaml

  2. Create a function:

    $ kn func create <function_name> -l <runtime>

  3. After you have created a new function project, you must add the project to a Git repository and ensure that the repository is available to the cluster. Information about this Git repository is used to update the func.yaml file in the next step.

  4. Update the configuration in the func.yaml file for your function project to enable on-cluster builds for the Git repository:

    ...
build: git (1)
git:
  url: <git_repository_url> (2)
  revision: main (3)
  contextDir: <directory_path> (4)
...
    1 Required. Specify git build type.
    2 Required. Specify the Git repository that contains your function’s source code.
    3 Optional. Specify the Git repository revision to be used. This can be a branch, tag or commit.
    4 Optional. Specify the function’s directory path if the function is not located in the Git repository root folder.

  5. Implement the business logic of your function. Then, use Git to commit and push the changes.

  6. Deploy your function:

    $ kn func deploy

    If you are not logged into the container registry referenced in your function configuration, you are prompted to provide credentials for the remote container registry that hosts the function image:

    Example output and prompts
    🕕 Creating Pipeline resources
Please provide credentials for image registry used by Pipeline.
? Server: https://index.docker.io/v1/
? Username: my-repo
? Password: ********
   Function deployed at URL: http://test-function.default.svc.cluster.local

  7. To update your function, commit and push new changes by using Git, then run the kn func deploy command again.

Deploying functions

You can deploy a function to your cluster as a Knative service by using the kn func deploy command. If the targeted function is already deployed, it is updated with a new container image that is pushed to a container image registry, and the Knative service is updated.

Prerequisites

  • The OpenShift Serverless Operator and Knative Serving are installed on the 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.

  • You must have already created and initialized the function that you want to deploy.

Procedure

  • Deploy a function:

    $ kn func deploy [-n <namespace> -p <path> -i <image>]
    Example output
    Function deployed at: http://func.example.com

    • If no namespace is specified, the function is deployed in the current namespace.

    • The function is deployed from the current directory, unless a path is specified.

    • The Knative service name is derived from the project name, and cannot be changed using this command.

Invoking a deployed function with a test event

You can use the kn func invoke cli command to send a test request to invoke a function either locally or on your OpenShift Container Platform cluster. This command can be used to test that a function is working and able to receive events correctly.

Example command
$ kn func invoke

The kn func invoke command executes on the local directory by default, and assumes that this directory is a function project.

Additional resources