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Chapter 2. 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.

2.1. Prerequisites
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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.

2.2. Creating functions
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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 quarkus, node, typescript, go, python, springboot, and rust.

    • Accepted template values include http and cloudevents.

      Example command

      $ kn func create -l typescript -t cloudevents examplefunc

      Example output

      Created typescript function in /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

      Created node function in /home/user/demo/examplefunc

2.3. Running a function locally
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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

2.4. Building functions
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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.

2.4.1. Image container types
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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

2.4.2. Image registry types
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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

2.4.3. Push flag
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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

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

Build help command

$ kn func help build

2.5. Deploying functions
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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.
Note

You can create a serverless function with a Git repository URL by using Import from Git or Create Serverless Function in the +Add view of the Developer perspective.

2.6. Invoking a deployed function with a test event
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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. You can use this command to test that a function is working and able to receive events correctly. Invoking a function locally is useful for a quick test during function development. Invoking a function on the cluster is useful for testing that is closer to the production environment.

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 deployed the function that you want to invoke.

Procedure

  • Invoke a function: 

    $ kn func invoke
    • The kn func invoke command only works when there is either a local container image currently running, or when there is a function deployed in the cluster.
    • The kn func invoke command executes on the local directory by default, and assumes that this directory is a function project.

2.7. Deleting a function
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You can delete a function by using the kn func delete command. This is useful when a function is no longer required, and can help to save resources on your cluster.

Procedure

  • Delete a function: 

    $ kn func delete [<function_name> -n <namespace> -p <path>]
    • If the name or path of the function to delete is not specified, the current directory is searched for a func.yaml file that is used to determine the function to delete.
    • If the namespace is not specified, it defaults to the namespace value in the func.yaml file.

2.9. Next steps
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