Extending the Kubernetes API

How to extend the Kubernetes API using CustomResourceDefinitions and CustomResources. Also, how to write a custom controller to operate on these CustomResources.

Presented as a talk at Kubernetes Pune meetup.

Transcript

1. Extending the Kubernetes API Thanks to Ashley McNamara for the wonderful artwork!
2. 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
3. What comes to your mind when you think of Kubernetes? @TheNikhita
4. What comes to your mind when you think of Kubernetes? Pods @TheNikhita
5. What comes to your mind when you think of Kubernetes? Pods Deployments @TheNikhita
6. What comes to your mind when you think of Kubernetes? Pods Deployments Services @TheNikhita
7. What comes to your mind when you think of Kubernetes? Pods Deployments Services StatefulSets DaemonSet CronJob ConfigMap Secrets Node PersistentVolumeClaim @TheNikhita
8. What comes to your mind when you think of Kubernetes? Pods Deployments Services StatefulSets DaemonSet CronJob ConfigMap Secrets Node PersistentVolumeClaim @TheNikhita
9. We are going to build our own objects! @TheNikhita
10. We are going to build our own objects! custom @TheNikhita
11. We are going to build our own custom resources! @TheNikhita
12. 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
13. Step 1: Tell Kubernetes about our object CustomResourceDefinition Step 2: Create the custom object CustomResource @TheNikhita
14. CustomResourceDefinition @TheNikhita
15. CustomResource @TheNikhita
16. DEMO TIME! @TheNikhita
17. What now? Let’s create a CONTROLLER (yes, you’ll have to write some code) @TheNikhita
18. CONTROLLER • Active reconciliation process Current state Desired state Status Spec @TheNikhita
19. 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
20. Kubernetes API structure Internal version External version(s) @TheNikhita
21. 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
22. 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
23. 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
24. 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
25. 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
26. 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
27. Thanks for coming!!!!