# Bitnami Secure Image for Cluster Autoscaler

## What is Cluster Autoscaler?

> Cluster Autoscaler is a component that automatically adjusts the size of a Kubernetes Cluster so that all pods have a place to run and there are no unneeded nodes.

[Overview of Cluster Autoscaler](https://github.com/kubernetes/autoscaler)
Trademarks: This software listing is packaged by Bitnami. The respective trademarks mentioned in the offering are owned by the respective companies, and use of them does not imply any affiliation or endorsement.

## TL;DR

```console
docker run --name cluster-autoscaler -e ALLOW_EMPTY_PASSWORD=yes bitnami/cluster-autoscaler:latest
```

**Warning**: These quick setups are only intended for development environments. You are encouraged to change the insecure default credentials and check out the available configuration options in the [Configuration](#configuration) section for a more secure deployment.

## Why use Bitnami Secure Images?

Those are hardened, minimal CVE images built and maintained by Bitnami. Bitnami Secure Images are based on the cloud-optimized, security-hardened enterprise [OS Photon Linux](https://vmware.github.io/photon/). Why choose BSI images?

- Hardened secure images of popular open source software with Near-Zero Vulnerabilities
- Vulnerability Triage & Prioritization with VEX Statements, KEV and EPSS Scores
- Compliance focus with FIPS, STIG, and air-gap options, including secure bill of materials (SBOM)
- Software supply chain provenance attestation through in-toto
- First class support for the internet’s favorite Helm charts

Each image comes with valuable security metadata. You can view the metadata in [our public catalog here](https://app-catalog.vmware.com/bitnami/apps). Note: Some data is only available with [commercial subscriptions to BSI](https://bitnami.com/).

![Alt text](https://github.com/bitnami/containers/blob/main/BSI%20UI%201.png?raw=true "Application details")
![Alt text](https://github.com/bitnami/containers/blob/main/BSI%20UI%202.png?raw=true "Packaging report")

If you are looking for our previous generation of images based on Debian Linux, please see the [Bitnami Legacy registry](https://hub.docker.com/u/bitnamilegacy).

## How to deploy Cluster Autoscaler in Kubernetes?

Cluster Autoscaler runs on the Kubernetes master node on most K8s cloud offerings.

> NOTE: It is possible to run customized Cluster Autoscaler inside of the cluster but then extra care needs to be taken to ensure that Cluster Autoscaler is up and running. User can put it into kube-system namespace (Cluster Autoscaler doesn't scale down node with non-manifest based kube-system pods running on them) and mark with scheduler.alpha.kubernetes.io/critical-pod annotation (so that the rescheduler, if enabled, will kill other pods to make space for it to run).

Currently, it is possible to run Cluster Autoscaler on:

* **AliCloud**: Consult [Cluster Autoscaler on AliCloud docs](https://github.com/kubernetes/autoscaler/blob/master/cluster-autoscaler/cloudprovider/alicloud/README.md).
* **AWS**: Consult [Cluster Autoscaler on AWS docs](https://github.com/kubernetes/autoscaler/blob/master/cluster-autoscaler/cloudprovider/aws/README.md).
* **Azure**: Consult [Cluster Autoscaler on Azure docs](https://github.com/kubernetes/autoscaler/blob/master/cluster-autoscaler/cloudprovider/azure/README.md).
* **GCE**: Consult [Cluster Autoscaler on GCE docs](https://kubernetes.io/docs/concepts/cluster-administration/cluster-management#upgrading-google-compute-engine-clusters).
* **GKE**: Consult [Cluster Autoscaler on GKE docs](https://cloud.google.com/container-engine/docs/cluster-autoscaler).

Please note that Cluster Autoscaler a series of permissions/privileges to adjusts the size of the K8s cluster. For instance, to run it on AWS, you need to:

* Provide the K8s worker node which runs the cluster autoscaler with a minimum IAM policy (check [permissions docs](https://github.com/kubernetes/autoscaler/tree/master/cluster-autoscaler/cloudprovider/aws#user-content-permissions) for more information).
* Create a service account for Cluster Autoscaler's deployment and bind to it some roles and cluster roles that provide the corresponding RBAC privileges.

> NOTE: Find resources to deploy Cluster Autoscaler on AWS in the [aws-examples](https://github.com/bitnami/containers/tree/main/bitnami/cluster-autoscaler/aws-examples) directory.

## Why use a non-root container?

Non-root container images add an extra layer of security and are generally recommended for production environments. However, because they run as a non-root user, privileged tasks are typically off-limits. Learn more about non-root containers [in our docs](https://techdocs.broadcom.com/us/en/vmware-tanzu/application-catalog/tanzu-application-catalog/services/tac-doc/apps-tutorials-work-with-non-root-containers-index.html).

## Supported tags and respective `Dockerfile` links

Learn more about the Bitnami tagging policy and the difference between rolling tags and immutable tags [in our documentation page](https://techdocs.broadcom.com/us/en/vmware-tanzu/application-catalog/tanzu-application-catalog/services/tac-doc/apps-tutorials-understand-rolling-tags-containers-index.html).

## Get this image

The recommended way to get the Bitnami Cluster-autoscaler Docker Image is to pull the prebuilt image from the [Docker Hub Registry](https://hub.docker.com/r/bitnami/cluster-autoscaler).

```console
docker pull bitnami/cluster-autoscaler:latest
```

To use a specific version, you can pull a versioned tag. You can view the [list of available versions](https://hub.docker.com/r/bitnami/cluster-autoscaler/tags/) in the Docker Hub Registry.

```console
docker pull bitnami/cluster-autoscaler:[TAG]
```

If you wish, you can also build the image yourself by cloning the repository, changing to the directory containing the Dockerfile and executing the `docker build` command. Remember to replace the `APP`, `VERSION` and `OPERATING-SYSTEM` path placeholders in the example command below with the correct values.

```console
git clone https://github.com/bitnami/containers.git
cd bitnami/APP/VERSION/OPERATING-SYSTEM
docker build -t bitnami/APP:latest .
```

## Configuration

### How to run a cluster with nodes in multiples zones for HA

`--balance-similar-node-groups` flag is intended to support this use case. If you set the flag to true, Cluster Autoscaler will automatically identify node groups with the same instance type and the same set of labels (except for automatically added zone label) and try to keep the sizes of those node groups balanced.

This does not guarantee similar node groups will have exactly the same sizes:

Currently the balancing is only done at scale-up. Cluster Autoscaler will still scale down underutilized nodes regardless of the relative sizes of underlying node groups.

### How monitor Cluster Autoscaler?

Cluster Autoscaler provides metrics and livenessProbe endpoints. By default they're available on port 8085 (configurable with --address flag), respectively under /metrics and /health-check.

Metrics are provided in Prometheus format.

### How scale my cluster to just 1 node?

Prior to version 0.6, Cluster Autoscaler was not touching nodes that were running important kube-system pods like DNS, Heapster, Dashboard etc. If these pods landed on different nodes, CA could not scale the cluster down and the user could end up with a completely empty 3 node cluster. In 0.6, we added an option to tell CA that some system pods can be moved around. If the user configures a PodDisruptionBudget for the kube-system pod, then the default strategy of not touching the node running this pod is overridden with PDB settings. So, to enable kube-system pods migration, one should set minAvailable to 0 (or <= N if there are N+1 pod replicas.) See also I have a couple of nodes with low utilization, but they are not scaled down. Why?

### How scale a node group to 0?

For GCE/GKE and for AWS, it is possible to scale a node group to 0 (and obviously from 0), assuming that all scale-down conditions are met.

For AWS, if you are using nodeSelector, you need to tag the ASG with a node-template key "k8s.io/cluster-autoscaler/node-template/label/".

For example, for a node label of foo=bar, you would tag the ASG with:

```yaml
{
    "ResourceType": "auto-scaling-group",
    "ResourceId": "foo.example.com",
    "PropagateAtLaunch": true,
    "Value": "bar",
    "Key": "k8s.io/cluster-autoscaler/node-template/label/foo"
}
```

### FIPS configuration in Bitnami Secure Images

The Bitnami Cluster Autoscaler Docker image from the [Bitnami Secure Images](https://go-vmware.broadcom.com/contact-us) catalog includes extra features and settings to configure the container with FIPS capabilities. You can configure the next environment variables:

- `OPENSSL_FIPS`: whether OpenSSL runs in FIPS mode or not. `yes` (default), `no`.

## Notable Changes

### Starting January 16, 2024

* The `docker-compose.yaml` file has been removed, as it was solely intended for internal testing purposes.

## License

Copyright &copy; 2026 Broadcom. The term "Broadcom" refers to Broadcom Inc. and/or its subsidiaries.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

<http://www.apache.org/licenses/LICENSE-2.0>

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
