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Downscaler

This section covers how to start development on the downscaler.

If you haven't already, read and follow the instructions for setting up the repository locally.

The files for the downscaler can mainly be found in ./cmd/kubedownscaler and ./internal.

Installing Prerequisite​

Before you start modifying the downscaler you should install its prerequisites.

Installing Go​

Installing go is necessary to be able to run the downscaler locally.

You can either use brew to install and update go:

brew install go

To update go using brew:

brew upgrade go

Or you can follow these instructions to install go another way.

After that you can check if your installation was successful.

go version

The output should be something like:

go version go1.23.2 linux/amd64

Installing Dependencies​

Once you have go installed you can start installing the Kubedownscalers dependencies.

go mod download

Running the Downscaler Locally​

To run the downscaler locally you need to specify a kubeconfig for it to use. The downscaler will use the current-context selected in the kubeconfig. The user of the selected context has to have the permissions required to scale.

go run ./cmd/kubedownscaler -k path/to/kubeconfig

Testing the Downscaler​

To test your code changes you should write or change existing tests to match your new functionality.

You can run all tests like this:

go test ./...

Compiling/Building​

You normally don't need to build the binary or docker image locally as workflows handle building those for releasing new versions. This is only necessary for e.g. testing the docker image.

Binary​

This is how you can build a binary of the kubedownscaler:

CGO_ENABLED=0 go build -o bin/gokubedownscaler ./cmd/kubedownscaler

Disabling CGO isn't strictly required although leaving it enabled does sometimes lead to problems.

Docker Image​

Building the Docker image is just like building any other Docker image:

docker build -t ghcr.io/caas-team/gokubedownscaler:someTag .

Running the Docker Image Locally​

To run the Docker container locally you also need to specify a kubeconfig.

docker run -v path/to/kubeconfig:/app/kubeconfig ghcr.io/caas-team/gokubedownscaler:latest -k=/app/kubeconfig