How to use this image

All examples in this guide use the public image. If you've mirrored the repository for your own use (for example, to your Docker Hub namespace), update your commands to reference the mirrored image instead of the public one.

For example:

• Public image: dhi.io/go-kube-downscaler:1
• Mirrored image: <your-namespace>/dhi-go-kube-downscaler:1

For the examples, you must first use docker login dhi.io to authenticate to the registry to pull the images.

GoKubeDownscaler is a Kubernetes controller that scales workloads down during a configured downtime window and restores them when the window ends. This image is that controller. It is the catalog replacement for ghcr.io/caas-team/gokubedownscaler on the 1.x line. Schedules and annotations are documented at https://kube-downscaler.io/⁠.

Debian 13 is the primary runtime tag: dhi.io/go-kube-downscaler:1. The same image is also published with the full version tag of the current 1.x release. The Alpine 3.24 runtime tag is dhi.io/go-kube-downscaler:1-alpine3.24.

Start a GoKubeDownscaler image

The entrypoint is /app/gokubedownscaler, a symlink to /usr/bin/gokubedownscaler. The image sets no command, no application environment variables, and no health check. The working directory is /.

Basic usage

--help exits 0 and writes usage to standard error. Standard output is empty. There is no version flag, and the binary prints no version string. Flags use Go's flag package. The printed form is a single dash, for example -once and -metrics.

docker run --rm dhi.io/go-kube-downscaler:1 --help

Runtime images run as user 65532 and contain no shell. dhi.io/go-kube-downscaler:1 and dhi.io/go-kube-downscaler:1-alpine3.24 cannot run bash or sh. Dev tags run as root and include a shell.

Ports

This image declares 8081/tcp and 8085/tcp. The upstream image does not expose those ports.

Port 8081 serves /healthz and /readyz. Those paths return HTTP 200 only after the process has created its Kubernetes client. They are not a substitute for a successful scale.

Port 8085 serves Prometheus metrics. It listens only when you pass -metrics. The default is off.

Run a downtime scan

A scan needs a kubeconfig via -k, or in-cluster configuration when the process runs inside the cluster. For a downtime window that does not name a time zone, the process reads DEFAULT_TIMEZONE from the environment you pass at start (for example UTC). This image does not set DEFAULT_TIMEZONE. Without a cluster the process exits non-zero.

• -once runs one scan and then exits. Without it, the process keeps scanning.
• -k selects a kubeconfig file instead of the in-cluster configuration.
• -namespace limits the scan to the namespaces you name. The default is every namespace.
• -grace-period sets the wait between workload creation and the first downscale. The usage text documents a 15-minute default.
• -default-downtime sets the timespans during which workloads are scaled down. Outside those timespans they are scaled up. The default is none.
• -dry-run prints the actions instead of applying them.

Dev variants

Dev images run as root and include a shell and a package manager. dhi.io/go-kube-downscaler:1-dev is Debian 13 with bash and apt-get. dhi.io/go-kube-downscaler:1-alpine3.24-dev is Alpine 3.24 with bash and apk.

docker run --rm --entrypoint bash dhi.io/go-kube-downscaler:1-dev -c 'command -v gokubedownscaler && gokubedownscaler --help >/tmp/h 2>&1 && grep -q -- -once /tmp/h'

docker run --rm --entrypoint bash dhi.io/go-kube-downscaler:1-alpine3.24-dev -c 'command -v gokubedownscaler && gokubedownscaler --help >/tmp/h 2>&1 && grep -q -- -once /tmp/h'

Upstream Helm chart

The upstream chart installs ghcr.io/caas-team/gokubedownscaler and sets podSecurityContext.runAsUser, runAsGroup, fsGroup, and supplementalGroups to 1000. This image runs as nonroot, uid 65532 and gid 65532. Pass these values so the chart selects dhi.io/go-kube-downscaler:1 and runs as 65532:65532. Leave arguments, includedResources, healthProbes, and the container securityContext unset so the chart defaults stay in place. Those defaults keep the chart's args and the /healthz and /readyz probes on port 8081.

image:
  repository: dhi.io/go-kube-downscaler
  tag: "1"
podSecurityContext:
  runAsNonRoot: true
  runAsUser: 65532
  runAsGroup: 65532
  fsGroup: 65532
  supplementalGroups: [65532]

Use tag 1-alpine3.24 for the Alpine runtime image. Leave webhookController.enabled false. That deployment uses ghcr.io/caas-team/gokubedownscaler-webhook, which this image does not supply.

Non-hardened images vs. Docker Hardened Images

The upstream image is a scratch image. Its user is empty, so the process runs as root, and it has no shell. Runtime tags of this image also have no shell, and they run as user 65532. A migration has to allow that user. Use a dev tag, or Docker Debug, when you need a shell.

This image declares ports 8081 and 8085. The upstream image does not. Port 8085 stays closed unless the process is started with -metrics.

Image variants

Docker Hardened Images come in different variants depending on their intended use. Image variants are identified by their tag.

• Runtime variants are designed to run your application in production. These images are intended to be used either directly or as the FROM image in the final stage of a multi-stage build. These images typically:

  • Run as a nonroot user
  • Do not include a shell or a package manager
  • Contain only the minimal set of libraries needed to run the app

• Build-time variants typically include dev in the tag name and are intended for use in the first stage of a multi-stage Dockerfile. These images typically:

  • Run as the root user
  • Include a shell and package manager
  • Are used to build or compile applications

• FIPS variants include fips in the variant name and tag. They come in both runtime and build-time variants. These variants use cryptographic modules that have been validated under FIPS 140, a U.S. government standard for secure cryptographic operations. For example, usage of MD5 fails in FIPS variants.

To view the image variants and get more information about them, select the Tags tab for this repository, and then select a tag.

Migrate to a Docker Hardened Image

To migrate your application to a Docker Hardened Image, you must update your Dockerfile. At minimum, you must update the base image in your existing Dockerfile to a Docker Hardened Image. This and a few other common changes are listed in the following table of migration notes.

The following steps outline the general migration process.

1. Find hardened images for your app.

   A hardened image may have several variants. Inspect the image tags and find the image variant that meets your needs.

2. Update the base image in your Dockerfile.

   Update the base image in your application's Dockerfile to the hardened image you found in the previous step. For framework images, this is typically going to be an image tagged as dev because it has the tools needed to install packages and dependencies.

3. For multi-stage Dockerfiles, update the runtime image in your Dockerfile.

   To ensure that your final image is as minimal as possible, you should use a multi-stage build. All stages in your Dockerfile should use a hardened image. While intermediary stages will typically use images tagged as dev, your final runtime stage should use a non-dev image variant.

4. Install additional packages

   Docker Hardened Images contain minimal packages in order to reduce the potential attack surface. You may need to install additional packages in your Dockerfile. Inspect the image variants to identify which packages are already installed.

   Only images tagged as dev typically have package managers. You should use a multi-stage Dockerfile to install the packages. Install the packages in the build stage that uses a dev image. Then, if needed, copy any necessary artifacts to the runtime stage that uses a non-dev image.

   For Alpine-based images, you can use apk to install packages. For Debian-based images, you can use apt-get to install packages.

Troubleshooting migration

The following are common issues that you may encounter during migration.

General debugging

The hardened images intended for runtime don't contain a shell nor any tools for debugging. The recommended method for debugging applications built with Docker Hardened Images is to use Docker Debug⁠ to attach to these containers. Docker Debug provides a shell, common debugging tools, and lets you install other tools in an ephemeral, writable layer that only exists during the debugging session.

Permissions

By default image variants intended for runtime, run as the nonroot user. Ensure that necessary files and directories are accessible to the nonroot user. You may need to copy files to different directories or change permissions so your application running as the nonroot user can access them.

Privileged ports

Non-dev hardened images run as a nonroot user by default. As a result, applications in these images can't bind to privileged ports (below 1024) when running in Kubernetes or in Docker Engine versions older than 20.10. To avoid issues, configure your application to listen on port 1025 or higher inside the container, even if you map it to a lower port on the host. For example, docker run -p 80:8080 my-image will work because the port inside the container is 8080, and docker run -p 80:81 my-image won't work because the port inside the container is 81.

No shell

By default, image variants intended for runtime don't contain a shell. Use dev images in build stages to run shell commands and then copy any necessary artifacts into the runtime stage. In addition, use Docker Debug to debug containers with no shell.

Entry point

Docker Hardened Images may have different entry points than images such as Docker Official Images. Use docker inspect to inspect entry points for Docker Hardened Images and update your Dockerfile if necessary.