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Java Function Buildpack

The Java Function Buildpack is a Cloud Native Buildpack that provides a Spring Boot application for executing functions.

Behaviour

This buildpack will participate if any of the following conditions are met:

  • A buildpack configuration variable BP_FUNCTION is explicitly set.
  • A file with the name func.yaml is detected.

The buildpack will do the following if detection passed:

  • Request for a JRE to be installed
  • Contributes the function invoker to a layer marked launch with the layer's path prepended to $CLASSPATH
  • Contributes environment variables defined in func.yaml to the launch layer
  • Contributes environment variables to configure the invoker if any configuration variables are defined. (Overrides anything from func.yaml)

Configuration

Environment Variable Description
$BP_FUNCTION Configure the function to load. If the function lives in the default package: <class>. If the function lives in their own package: <package>.<class>. Defaults to functions.Handler

Getting started

To get started you'll need to create a directory where your function will be defined.

From within this directory we require a few files to properly detect this as a Java function:

  • func.yaml (optional): We use this to configure the runtime environment variables. This buildpack makes use of envs and options. The keys name and runtime are required to maintain compatibility with Knative func cli, but are not used by this buildpack. See Knative's func.yaml documentation for more func.yaml information.
  • pom.xml or build.gradle: These are used by the other Java buildpacks to compile your function.
  • Java package in folder src/main/java/functions: This is the default location your function will be detected. If you do choose to use another package to store your functions, you will need to define where your function is located with the BP_FUNCTION configuration for the buildpack.

Compiling Your Function

To compile your function with the buildpack, we've provided a builder which has all the pre-requisites ready to go. You can find it on github.

ghcr.io/vmware-tanzu/function-buildpacks-for-knative/functions-builder

Prerequisites

Usage

Build the function container with the Buildpack CLI

pack build <your_image_name_and_tag> --builder ghcr.io/vmware-tanzu/function-buildpacks-for-knative/functions-builder:<version> --env BP_JVM_VERSION=17

Publish it to your registry:

docker push <your_image_name_and_tag>

Liveness / Readiness Endpoints

The Java invoker contains a readiness/liveness endpoint that can be hit at localhost:8080/actuator/health by default. For more information, please read about the Spring Boot Actuator's Kubernetes Probes.

Templates

If you want to quickly start writing your functions, take a look at the templates/java folder at the root of this repo.

Examples

For some inspiration, take a look at the samples/java folder at the root of this repo.