# Cluster Autoscaler packaged by Bitnami

## 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/tree/master/cluster-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 redis -e ALLOW_EMPTY_PASSWORD=yes bitnami/cluster-autoscaler:latest
```

#### Docker Compose

```console
$ curl -sSL https://raw.githubusercontent.com/bitnami/containers/main/bitnami/cluster-autoscaler/docker-compose.yml > docker-compose.yml
$ docker-compose up -d
```

**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.

## 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/tree/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#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](./aws-examples) directory.

## Why use Bitnami Images?

* Bitnami closely tracks upstream source changes and promptly publishes new versions of this image using our automated systems.
* With Bitnami images the latest bug fixes and features are available as soon as possible.
* Bitnami containers, virtual machines and cloud images use the same components and configuration approach - making it easy to switch between formats based on your project needs.
* All our images are based on [minideb](https://github.com/bitnami/minideb) a minimalist Debian based container image which gives you a small base container image and the familiarity of a leading Linux distribution.
* All Bitnami images available in Docker Hub are signed with [Docker Content Trust (DCT)](https://docs.docker.com/engine/security/trust/content_trust/). You can use `DOCKER_CONTENT_TRUST=1` to verify the integrity of the images.
* Bitnami container images are released on a regular basis with the latest distribution packages available.

## 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://docs.bitnami.com/tutorials/work-with-non-root-containers/).

## 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://docs.bitnami.com/tutorials/understand-rolling-tags-containers/).


* [`1`, `1-debian-11`, `1.24.0`, `1.24.0-debian-11-r31`, `latest` (1/debian-11/Dockerfile)](https://github.com/bitnami/containers/blob/main/bitnami/cluster-autoscaler/1/debian-11/Dockerfile)

Subscribe to project updates by watching the [bitnami/containers GitHub repo](https://github.com/bitnami/containers).

## 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"
}
```

## Contributing

We'd love for you to contribute to this container. You can request new features by creating an [issue](https://github.com/bitnami/containers/issues), or submit a [pull request](https://github.com/bitnami/containers/pulls) with your contribution.

## Issues

If you encountered a problem running this container, you can file an [issue](https://github.com/bitnami/containers/issues/new/choose). For us to provide better support, be sure to fill the issue template.

### Community supported solution

Please, note this asset is a community-supported solution. This means that the Bitnami team is not actively working on new features/improvements nor providing support through GitHub Issues. Any new issue will stay open for 20 days to allow the community to contribute, after 15 days without activity the issue will be marked as stale being closed after 5 days.

The Bitnami team will review any PR that is created, feel free to create a PR if you find any issue or want to implement a new feature.

New versions and releases cadence are not going to be affected. Once a new version is released in the upstream project, the Bitnami container image will be updated to use the latest version, supporting the different branches supported by the upstream project as usual.

## License
Copyright &copy; 2022 Bitnami

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.
