k8s-cronjob-prescaler/README.md

Project Status & Disclaimer

The code provided in this repo is not actively maintained.

Introduction

The main purpose of this project is to provide a mechanism whereby cronjobs can be run on auto-scaling clusters, and ensure that the cluster is scaled up to their desired size prior to the time at which the CronJob workload needs to begin.

Example

For a workload to start at 16:30 exactly, a node in the cluster has to be available and warm at that time. The PrescaledCronJob CRD and operator will ensure that a cronjob gets scheduled n minutes earlier to force the cluster to prepare a node, and then a custom init container will run, blocking the workload running until the correct time.

How it works

• This project defines a new Kubernetes CRD kind named PreScaledCronJob; and an Operator that will reconcile said kind.
• When a PreScaledCronJob is created in a cluster, this Operator will create an associated CronJob object that will execute X minutes prior to the real workload and ensure any necessary agent pool machines are "warmed up".
  • More information on how we calculate the CronJob schedule can be found in the Primed Cronjob Schedules documentation here
• The created CronJob is associated to the PreScaledCronJob using the Kubernetes OwnerReference mechanism. Thus enabling us to automatically delete the CronJob when the PreScaledCronJob resource is deleted. For more information please check out the Kubernetes documentation here
• PreScaledCronJob objects can check for changes on their associated CronJob objects via a generated hash. If this hash does not match that which the PreScaledCronJob expects, we update the CronJob spec.
• The generated CronJob uses an initContainer spec to spin-wait thus warming up the agent pool and forcing it to scale up to our desired state ahead of the real workload. For more information please check out the Init Container documentation here

Getting Started

1. Clone the codebase
2. Ensure you have Docker installed and all necessary pre-requisites to develop on remote containers installation notes
3. Install VSCode Remote Development extensions pack
4. Open the project and run in the development container

Build And Deploy

NOTE: In order to ensure a smooth deployment process, for both local and remote deployments, we recommend you use the dev container provided within this repo. This container provides you with all the assemblies and cli tools required to perform the actions below

Deploying locally

If you are using the development container you have the option of deploying the Operator into a local test Kubernetes Cluster provided by the KIND toolset

To deploy to a local K8s/Kind instance:

make deploy-kind

Deploying to a remote cluster

Prerequisites

• Ensure your terminal is connected to your K8s cluster
• Ensure your terminal is logged into your docker container registry that you will be using as the image store for your K8s cluster
• Ensure your cluster has permissions to pull containers from your container registry

Deploying

1. Deploy the image used to initialise cluster scale up:

  make docker-build-initcontainer docker-push-initcontainer INIT_IMG=<some-registry>/initcontainer:<tag>

2. Deploy the operator to your cluster:

  make docker-build docker-push IMG=<some-registry>/prescaledcronjoboperator:<tag> INIT_IMG=<some-registry>/initcontainer:<tag>

  make deploy-cluster IMG=<some-registry>/prescaledcronjoboperator:<tag> INIT_IMG=<some-registry>/initcontainer:<tag>

3. Once the deployment is complete you can check that everything is installed:

  kubectl get all -n psc-system

Creating your first PreScaledCronJob

A sample yaml is provided for you in the config folder.

• To apply this:

  kubectl apply -f config/samples/psc_v1alpha1_prescaledcronjob.yaml

• To test the Operator worked correctly:

  kubectl get prescaledcronjobs -A
  kubectl get cronjobs -A

• If everything worked correctly you should see the following output:

NAMESPACE    NAME                      AGE
psc-system   prescaledcronjob-sample   30s

NAMESPACE    NAME                              SCHEDULE        SUSPEND   ACTIVE   LAST SCHEDULE   AGE
psc-system   autogen-prescaledcronjob-sample   45,15 * * * *   False     0        <none>          39s

If you do not see the ouput above then please review the debugging documentation. Deleting the PrescaledCronJob resource will clean up the CronJob automatically.

Define Primer Schedule

Before the actual cronjob kicks off, an init container pre-warms the cluster so all nodes are immediately available when the cronjob is intended to run.

There are two ways to define this primer schedule:

1. Set warmUpTimeMins under the PreScaledCronJob spec. This will generate a primed cronjob schedule based on your original schedule and the amount of minutes you want to pre-warm your cluster. This can be defined as follows (An example yaml is provided in config/samples/psc_v1alpha1_prescaledcronjob.yaml):

kind: PreScaledCronJob
spec:
  warmUpTimeMins: 5
  cronJob:
    spec:
      schedule: "5/30 * * * *"

• OR -

2. Set a pre-defined primerSchedule under the PreScaledCronJob. The pre-defined primer schedule below results in the exact same pre-warming and cron schedule as the schedule above. (An example yaml is provided in config/samples/psc_v1alpha1_prescaledcronjob_primerschedule.yaml)

kind: PreScaledCronJob
spec:
  primerSchedule: "*/30 * * * *"
  cronJob:
    spec:
      schedule: "5/30 * * * *"

Debugging

Please review the debugging documentation

Monitoring

Please review the monitoring documentation

Running the Tests

This repo contains 3 types of tests, which are logically separated:

• Unit tests, run with go test.
  • To run: make unit-tests.
• 'Local' Integration tests, which run in a KIND cluster and test that the operator outputs the objects we expect.
  • To run: make kind-tests
• 'Long' Integration tests, also running in KIND which submit objects to the cluster and monitor the cluster to ensure jobs start at the right time.
  • To run: make kind-long-tests

Hints and Tips

• Run make fmt to automatically format your code

Kustomize patching

Many samples in the Kubernetes docs show requests and limits of a container using plain integer values, such as:

requests:
  nvidia.com/gpu: 1

The generated yaml schema definition for the PrescaledCronJob just sets the validation for these properties to strings, rather than what they should be (integer | string with a fixed regex format). This means we need to apply a patch (/config/crd/patches/resource-type-patch.yaml) to override the autogenerated type. This information may come in handy in future if other edge cases are found.