Kubernetes Schedule Scaler

Kubernetes Schedule Scaler allows you to change the number of running replicas of a Deployment at specific times. It can be used is to turn on/off applications that don't need to be always available and reduce cluster resource utilization, or to adjust the number of replicas when it's known in advance how the traffic volume is distributed across different time periods.

Installation

$ kubectl apply -f https://github.com/citizensadvice/kube-schedule-scaler/raw/master/deploy/deployment.yaml

Usage

Just add the annotation to your Deployment:

  annotations:
    zalando.org/schedule-actions: '[{"schedule": "10 18 * * *", "replicas": "3"}]'

The following fields are available:

• schedule - cron expression for the schedule
• tz - timezone override (e.g. Europe/London)
• replicas - the number of replicas to scale to
• minReplicas - in combination with an HorizontalPodAutoscaler, will adjust the min number of replicas
• maxReplicas - in combination with an HorizontalPodAutoscaler, will adjust the max number of replicas

Deployment Example

kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    application: nginx-deployment
  annotations:
    zalando.org/schedule-actions: |
      [
        {"schedule": "0 7 * * Mon-Fri", "replicas": "1"},
        {"schedule": "0 19 * * Mon-Fri", "replicas": "0"},
        {"schedule": "0 12 * * Mon-Fri", "minReplicas": "2", "maxReplicas": "3"},
        {"schedule": "0 16 * * Mon-Fri", "minReplicas": "1"}
      ]

When your Deployment is not managed by an HorizontalPodAutoscaler, setting replicas to the desired number of replicas is sufficient.

When an HorizontalPodAutoscaler is managing the Deployment, it will ignore the Deployment if replicas is set to 0, so setting replicas to and 1 and 0 acts as a switch on/off for the application, while minReplicas and maxReplicas can be used to adjust the desired number of replicas.

In order for the HorizontalPodAutoscaler to be detected, it must be called with the same name as the Deployment that manages.

Debugging

If your scaling action has not been executed for some reason, you can check with the steps below:

$ kubectl get pods -n kube-schedule-scaler
NAME                                    READY   STATUS    RESTARTS   AGE
kube-schedule-scaler-844b6d5888-p9tc4   1/1     Running   0          3m12s

Check the logs for your specific deployment:

$ kubectl logs -n kube-schedule-scaler kube-schedule-scaler-844b6d5888-p9tc4 | grep -i 'nginx'
17-06-2020 20:11:00 INFO - main.py:131 - Deployment default/nginx scaled to 1 replicas
17-06-2020 20:12:00 INFO - main.py:169 - HPA default/nginx minReplicas set to 3
17-06-2020 20:12:00 INFO - main.py:171 - HPA default/nginx maxReplicas set to 4
17-06-2020 20:13:00 INFO - main.py:169 - HPA default/nginx minReplicas set to 1
17-06-2020 20:13:00 INFO - main.py:171 - HPA default/nginx maxReplicas set to 2

Check for specific deployment at specific time:

$ kubectl logs -n kube-schedule-scaler kube-schedule-scaler-844b6d5888-p9tc4 | grep -i 'nginx' | grep '20:12'
17-06-2020 20:12:00 INFO - main.py:169 - HPA default/nginx minReplicas set to 3
17-06-2020 20:12:00 INFO - main.py:171 - HPA default/nginx maxReplicas set to 4

You can change the log level using the LOG_LEVEL environment variable (e.g. LOG_LEVEL=DEBUG)

Testing

To run the tests you will need:

• kube-schedule-scaler installed in a working k8s cluster (e.g. Minikube)
• pytest (can be installed with pip, in a virtualenv for example)

The tests will create some deployment and hpa resources with the proper annotation and verify that they are scaled properly. If you want to test your local build, you can run it in Minikube.