Custom Resources for Cloud Native DevOps

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FIND ME github.com/jelmersnoeck twitter.com/jelmersnoeck Jelmer Snoeck ABOUT ME - OX Tech Lead at manifold.co - Kubernetes - Terraform - Kubelist Editor

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$ tree custom-resources-cloud-native-devops/ - What are Custom Resources - How to build Custom Resources - Publishing Custom Resources

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Custom Resource (Definitions) Photo by The Roaming Platypus on Unsplash

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A custom resource is an extension of the Kubernetes API that is not necessarily available on every Kubernetes cluster. In other words, it represents a customization of a particular Kubernetes installation.

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Custom Resource Definition (CRD)

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The CustomResourceDefinition API resource allows you to define custom resources. Defining a CRD object creates a new custom resource with a name and schema that you specify. The Kubernetes API serves and handles the storage of your custom resource.

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Validation

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Open API Schema

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Admission Webhooks

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Printer Columns

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Finalizers

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Controller vs Operator

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Controller <> Operator - Controller purely interacts with k8s objects (even custom ones) - Operator knows about a different domain outside of k8s (etcd, prometheus, …)

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Some CRDs in the wild

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- cert-manager - prometheus-operator - ingress-nginx-controller - contour - ingress-monitor - istio Examples

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What’s under the hood Photo by Wade Lambert on Unsplash

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Defining APIs

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API Definitions

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Generated runtime.Object code

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type Object interface { GetObjectKind() schema.ObjectKind DeepCopyObject() Object }

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Scheme Definitions

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Generating Clients

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k8s.io/code-generator/generate-groups.sh

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./vendor/k8s.io/code-generator/generate-groups.sh \ all \ github.com/jelmersnoeck/ingress-monitor/pkg/client/generated \ github.com/jelmersnoeck/ingress-monitor/apis \ ingressmonitor:v1alpha1 \ --go-header-file boilerplate.go.txt

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Controller

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Cache Informers

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Event Handlers

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type ResourceEventHandler interface { OnAdd(obj interface{}) OnUpdate(oldObj, newObj interface{}) OnDelete(obj interface{}) }

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Workqueue

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Built in queue features ● Fair: items processed in the order in which they are added. ● Stingy: a single item will not be processed multiple times concurrently, and if an item is added multiple times before it can be processed, it will only be processed once. ● Multiple consumers and producers. In particular, it is allowed for an item to be reenqueued while it is being processed. ● Shutdown notifications.

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Label Selectors

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Labels

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Survive Rescheduling

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Testing

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Testing - Fake Clients - Add wrappers to test informers - Use of testing.Fake Actions