Build and run functions locally

The STACKIT Function CLI contains commands that simplify the process of building and running a function locally.

Building STACKIT Functions images is handled using Cloud Native Buildpacks, a CNCF project for automatically detecting source code requirements and building images, without requiring complicated configuration.

Note: both building and running functions, require a running Docker installation, accessible over a Unix domain socket in $DOCKER_HOST (or over the default /var/run/docker.sock socket). Full support for alternative OCI runtimes, especially Podman, will come in later releases.

Build a function

To build a function, run the following command in the project directory created by sfn function bootstrap:

cd <path-to-functions-project>
sfn function build

When running the build command for the first time, it will error out because you don’t have an image name configured yet. Configure one with the --image flag:

sfn function build --image <your OCI registry>/<repository>/<image name>:<tag>

Finally, to see the messages printed by the build process, pass the --verbose flag to the sfn function build command:

sfn function build --verbose

Run a function locally

Once you have built a function, you can run it with the run subcommand:

sfn function run

This will start a Docker container with your function, in a simulation of the STACKIT functions environment.

You can access the running function at http://127.0.0.1:8080 by default, unless you override the port the CLI binds to with the --address flag. Meanwhile, the sfn CLI will forward the log messages from your locally-running function, which you can use for debugging purposes.

Defining local memory limits

To mimic the deployment you can limit the memory configuration when testing functions on your local machine. The only thing you have to do is to define localLimits memory in your stackit-functions.yaml manifest file, and then to run your function locally, e.g.:

local_limits:
  memory: 640

The unit of the memory parameter is MegaBytes