Extending the Kubernetes API Thanks to Ashley McNamara for the wonderful artwork! 

Who am I? ● Hi, I am Nikhita Raghunath! ● Google Summer of Code student for CNCF (Kubernetes) ● Undergrad student from VJTI, Mumbai You can find me on: ➔ Twitter: @TheNikhita ➔ Github: nikhita ➔ Website: https://www.nikhita.github.io @TheNikhita 

What comes to your mind when you think of Kubernetes? @TheNikhita 

What comes to your mind when you think of Kubernetes? Pods @TheNikhita 

What comes to your mind when you think of Kubernetes? Pods Deployments @TheNikhita 

What comes to your mind when you think of Kubernetes? Pods Deployments Services @TheNikhita 

What comes to your mind when you think of Kubernetes? Pods Deployments Services StatefulSets DaemonSet CronJob ConfigMap Secrets Node PersistentVolumeClaim @TheNikhita 

What comes to your mind when you think of Kubernetes? Pods Deployments Services StatefulSets DaemonSet CronJob ConfigMap Secrets Node PersistentVolumeClaim @TheNikhita 

We are going to build our own objects! @TheNikhita 

We are going to build our own objects! custom @TheNikhita 

We are going to build our own custom resources! @TheNikhita 

We are going to build our own custom resources! That’s cool. But...why? Operator pattern: encode domain knowledge for specific applications as an extension of Kubernetes API. @TheNikhita 

Step 1: Tell Kubernetes about our object CustomResourceDefinition Step 2: Create the custom object CustomResource @TheNikhita 

CustomResourceDefinition @TheNikhita 

CustomResource @TheNikhita 

DEMO TIME! @TheNikhita 

What now? Let’s create a CONTROLLER (yes, you’ll have to write some code) @TheNikhita 

CONTROLLER ● Active reconciliation process Current state Desired state Status Spec @TheNikhita 

What will our controller do? 1. Try to make the current state same as the desired state. 2. Do something extra on add, update, delete of a resource. Example: - Write a message in a CustomResource. - Create the CustomResource. - A Github comment is created with this message. Link: https://github.com/nikhita/kube-custom-controller (inspired from https://github.com/munnerz/k8s-api-pager-demo) @TheNikhita 

Kubernetes API structure Internal version External version(s) @TheNikhita 

Step 1: Create internal types Inside pkg/apis/github - doc.go - register.go - types.go Step 2: Create external types Inside pkg/apis/github/v1 - doc.go - register.go - types.go Step 3: Install your API group Inside pkg/apis/github/install - install.go @TheNikhita 

Step 4: GENERATE CODE! Use https://github.com/kubernetes/code-generator 1. client-gen 2. conversion-gen 3. deepcopy-gen 4. defaulter-gen 5. informer-gen 6. lister-gen @TheNikhita 

Step 5: Create the controller 1. Create clients: - kubernetes client => kubeconfig file - github client => github API token 2. Create an informer: Use sharedInformers: - notify or “inform” about add/update/delete of a resource - use a common cache across all controllers @TheNikhita 

Step 5: Create the controller 3. Add event handler to the informer: - to tell what happens on add/update/delete - here, we will put it into a queue 4. Start the informer - wait for the informer cache sync across all resources @TheNikhita 

Step 5: Create the controller 5. Take the object from the queue: - take the object from the queue - get it’s latest version - sync it! 6. Sync it! (current state -> desired state): - do some action. Here, we send a Github comment. - update the status (the current state) - update the resource @TheNikhita 

That’s it! We learnt how to: - Create a CustomResourceDefinition - Create a CustomResource - Write your own controller to use the CustomResource! If you have even more specific needs, you should use Aggregated API Servers....but we won’t be discussing that today. @TheNikhita 

Thanks for coming!!!!