/kubebuilder-cronjob

Primary LanguageGo

kubebuilder cronjob

https://book.kubebuilder.io/cronjob-tutorial/

Kustomize /config

  • Kustomize YAML defs for launching controller in cluster
  • Kustomize base in config/default
  • config/manager: Launch controllers as pods in cluster
  • /config/rbac: permissions required to run controllers under svc acct

controller runtime manager in main.go

  • Runs all of our controllers and webhooks;
  • Sets up clients to API server

Kubernetes: Kinds, Resources

Convention: resources are always the lowercase form of the Kind

  • Kind: API type
  • Resource: A usage of a Kind in the API
  • Usually a 1:1 mapping between Kinds and resources, but with CRDs, each Kind corresponds to a single resource
  • Go: GVK for GroupVersionKind
  • Go: GVR for GroupVersionResource
  • Scheme: tracking what Go type (GVR) corresponds to a GVK. (see groupversion_info.go)

CRDs, Controller, API

CRDs are the canonical API for custom resources;

... Controllers are the API's business logic;

... Controllers reconcile state and spec.

API: Create Custom Resources and CRDs for our Kinds

CRDs are a definition of our customized Objects, and the CRs are an instance of it.

  • New APIs are how we teach Kubernetes about our custom objects;
  • Go structs generate a CRD, which includes the data schema
  • We then create instances of our custom objects;
  • Those instances are managed by controllers. Controllers manage the CR.

Add new API

  • Add API. Add new resource and controller, too. 
    kubebuilder create api --group batch --version v1 --kind CronJob
  • This creates /api/vi dir which corresponds to batch.{DOMAIN}/v1 per our --domain settings from earlier, so ours would be batch.example.com/v1.
  • This also creates file for Cronjob Kind, /api/v1/cronjob_types.go;
  • Each time we call the command with a different Kind, a new file will be created!

API: Defining Types according to Kinds

Cronjob Kind file cronjob_types.go

  • All Kubernetes objects have:
  • TypeMeta (API Version and Kind)
  • Objectmeta (name, namespace, labels)

Struct tags for serialization

controller-tools will use markers to generate CRD manifest

runtime.Object interface

  • all types representing Kinds must implement this
  • kubebuilder generates this via marker comments for controller-tools codegen
  • marker comments for codegen look like +kubebuilder:object:root=true
  • See zz_generated.deepcopy.go which contains the autogen implementation of runtime.Object interface.
  • The core of the runtime.Object interface is a deep-copy method, DeepCopyObject.

Spec CronJobSpec : Desired State (controller input!)

What does a cronjob need? a cron and a job. Deadlines are nice to have too, and handling concurrency is nice.

  • This is why our CronjobSpec struct has fields for these concerns.

Remember, we don't read our own Status; we use old jobs instead to keep track of whether a job has run.

Status CronJobStatus : observed state

Remember that we don't read our own Status; we use old jobs to do this instead. Contains any information we want users or other controllers to get

  • List of actively running jobs, and, the last time we successfully ran a job.