The document outlines the extensibility of Kubernetes through custom resources and custom resource definitions (CRDs), which allow users to define unique API objects not available in all clusters. It also discusses the role of controllers, which are necessary for implementing logic and managing these custom resources, along with real-world applications such as lambdas and service meshes. Additionally, it introduces Kyma, a cloud-native application development framework that integrates various open-source projects for building applications on Kubernetes.

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Kubernetes extensibility
with Custom Resources
Piotr Bochyński

2. Copyright © 2018 The Kyma project authors.
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