# Kube Descheduler Operator

Run the descheduler in your OpenShift cluster to move pods based on specific strategies.

## Deploy the operator

### Quick Development

1. Build and push the operator image to a registry:
2. Ensure the `image` spec in `deploy/05_deployment.yaml` refers to the operator image you pushed
3. Run `oc create -f deploy/.`

### OperatorHub install with custom index image

This process refers to building the operator in a way that it can be installed locally via the OperatorHub with a custom index image

1. build and push the image to a registry (e.g. https://quay.io):
   ```sh
   $ podman build -t quay.io/<username>/ose-cluster-kube-descheduler-operator-bundle:latest -f Dockerfile .
   $ podman push quay.io/<username>/ose-cluster-kube-descheduler-operator-bundle:latest
   ```

1. build and push image index for operator-registry (pull and build https://github.com/operator-framework/operator-registry/ to get the `opm` binary)
   ```sh
   $ ./bin/linux-amd64-opm index add --bundles quay.io/<username>/ose-cluster-kube-descheduler-operator-bundle:latest --tag quay.io/<username>/ose-cluster-kube-descheduler-operator-bundle-index:1.0.0
   $ podman push quay.io/<username>/ose-cluster-kube-descheduler-operator-bundle-index:1.0.0
   ```

   Don't forget to increase the number of open files, .e.g. `ulimit -n 100000` in case the current limit is insufficient.

1. create and apply catalogsource manifest:
   ```yaml
   apiVersion: operators.coreos.com/v1alpha1
   kind: CatalogSource
   metadata:
     name: cluster-kube-descheduler-operator
     namespace: openshift-marketplace
   spec:
     sourceType: grpc
     image: quay.io/<username>/ose-cluster-kube-descheduler-operator-bundle-index:1.0.0
   ```

1. create `cluster-kube-descheduler-operator` namespace:
   ```
   $ oc create ns cluster-kube-descheduler-operator
   ```

1. open the console Operators -> OperatorHub, search for `descheduler operator` and install the operator

## Sample CR

A sample CR definition looks like below (the operator expects `cluster` CR under `openshift-kube-descheduler-operator` namespace):

```yaml
apiVersion: operator.openshift.io/v1beta1
kind: KubeDescheduler
metadata:
  name: cluster
  namespace: openshift-kube-descheduler-operator
spec:
  deschedulingIntervalSeconds: 1800
  profiles:
  - AffinityAndTaints
```

The operator spec provides a `profiles` field, which allows users to set one or more descheduling profiles to enable.

These profiles map to preconfigured policy definitions, enabling several descheduler strategies grouped by intent, and 
any that are enabled will be merged.

## Profiles

The following profiles are currently provided:
* [`AffinityAndTaints`](#AffinityAndTaints)
* [`TopologyAndDuplicates`](#TopologyAndDuplicates)
* [`LifecycleAndUtilization`](#LifecycleAndUtilization)

Each of these enables cluster-wide descheduling (excluding openshift and kube-system namespaces) based on certain goals.

### AffinityAndTaints
This is the most basic descheduling profile and it removes running pods which violate node and pod affinity, and node 
taints.

This profile enables the [`RemovePodsViolatingInterPodAntiAffinity`](https://github.com/kubernetes-sigs/descheduler/#removepodsviolatinginterpodantiaffinity), 
[`RemovePodsViolatingNodeAffinity`](https://github.com/kubernetes-sigs/descheduler/#removepodsviolatingnodeaffinity), and 
[`RemovePodsViolatingNodeTaints`](https://github.com/kubernetes-sigs/descheduler/#removepodsviolatingnodeaffinity) strategies.

### TopologyAndDuplicates
This profile attempts to balance pod distribution based on topology constraint definitions and evicting duplicate copies 
of the same pod running on the same node. It enables the [`RemovePodsViolatingTopologySpreadConstraints`](https://github.com/kubernetes-sigs/descheduler/#removepodsviolatingtopologyspreadconstraint) 
and [`RemoveDuplicates`](https://github.com/kubernetes-sigs/descheduler/#removeduplicates) strategies.

### LifecycleAndUtilization
This profile focuses on pod lifecycles and node resource consumption. It will evict any running pod older than 24 hours 
and attempts to evict pods from "high utilization" nodes that can fit onto "low utilization" nodes. A high utilization 
node is any node consuming more than 50% its available cpu, memory, *or* pod capacity. A low utilization node is any node 
with less than 20% of its available cpu, memory, *and* pod capacity.

This profile enables the [`LowNodeUtilizaition`](https://github.com/kubernetes-sigs/descheduler/#lownodeutilization) and 
[`PodLifeTime`](https://github.com/kubernetes-sigs/descheduler/#podlifetime) strategies. In the future, more configuration 
may be made available through the operator for these strategies based on user feedback.

## How does the descheduler operator work?

Descheduler operator at a high level is responsible for watching the above CR
- Create a configmap that could be used by descheduler.
- Run descheduler as a deployment mounting the configmap as a policy file in the pod.

The configmap created from above sample CR definition looks like this:

```yaml
apiVersion: descheduler/v1alpha1
    kind: DeschedulerPolicy
    strategies:
      RemovePodsViolatingInterPodAntiAffinity:
        enabled: true
        ...
      RemovePodsViolatingNodeAffinity:
        enabled: true
        params:
          ...
          nodeAffinityType:
          - requiredDuringSchedulingIgnoredDuringExecution
      RemovePodsViolatingNodeTaints:
        enabled: true
        ...
```
(Some generated parameters omitted.)


## Parameters
The Descheduler operator exposes the following parameters in its CRD:

* `deschedulingIntervalSeconds` - this sets the number of seconds between descheduler runs
* `profiles` - which descheduler profiles that are enabled
