How to extend K8S with custom resource. Lecture provided by Piotr Bochynski within the program HackYourCareer

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Kubernetes extensibility
with Custom Resources
Piotr Bochyński

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Agenda
Kubernetes API
Custom Resources & Custom
Resource Definitions
Controllers
Real World Use Cases
Lambdas (serverless functions)
Service Mesh (istio)
Service Catalog & Bindings (declarative
connection to the service)

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Kubernetes API
A resource is an endpoint in the Kubernetes API that stores a collection of API
objects of a certain kind. Examples:
• deployments
• pods
• services
You can add new custom resource using:
• CRDs (simple)
• API Aggregation (more complex, but allows more control over API behaviors like
how data is stored and conversion between API versions)

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Custom Resources
A custom resource is an extension of the Kubernetes API that is not necessarily available
on every Kubernetes cluster.
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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Custom Resources
apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
name: foos.samplecontroller.k8s.io
spec:
group: samplecontroller.k8s.io
version: v1alpha1
names:
kind: Foo
plural: foos
scope: Namespaced
validation:
openAPIV3Schema:
properties:
spec:
properties:
replicas:
type: integer
minimum: 1
maximum: 10
apiVersion: samplecontroller.k8s.io/v1alpha1
kind: Foo
metadata:
name: example-foo
spec:
deploymentName: example-foo
replicas: 1

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DEMO – create custom
resource

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Controllers
Custom resources without controllers are rather useless.
You need some logic.
Controllers use reconcilliation loop pattern

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Controllers
Kubernetes provide tools to simplify development of controllers

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kubernetes/sample-controller
DEMO & quick walk through

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Real World Use Cases
Lambdas - Kubeless
• Kubeless is a serverless engine designed for kubernetes
• Function is defined as Custom Resource
• Function can be triggered by http request or event
Service Mesh – Istio
• Traffic controll (incoming, internal and outgoing)
• Security
• Monitoring and tracing

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DEMO: create Custom resources
for lambda function and API

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Service Binding

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Alternatives
• https://github.com/kubernetes-
sigs/kubebuilder
• https://github.com/operator-
framework/operator-sdk

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WANT MORE?

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What is Kyma?
Kyma is a cloud-native application development framework.
It provides the last mile capabilities that a developer needs
to build a cloud-native application using several open-source
projects such as Kubernetes, Istio, NATS, Kubeless, and
Prometheus, to name a few.
It is designed natively on Kubernetes and, therefore,
it is portable to all major cloud providers.

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Thank you
Piotr Bochynski
twitter: @pbochynski
mail: piotr.bochynski@sap.com