Most people talk to their Kubernetes clusters using the kubectl tool, but we’re seeing more and more cases where engineers are writing their own software to talk to the Kubernetes API itself. The use cases for doing so are many: writing ingress controllers, managing pods and watching logs to name a few. At Deis, we’re using the Kubernetes Go SDK for quite a few different purposes. We first started by vendoring in the Kubernetes mono-repo to watch pod events. We pushed our code to production and quickly learned all about Kubernetes event stream internals and the server-side event cache. When we got something working reliably, we expanded our usage of this client code to a few other domains. We later migrated to the the client-go package when it was released and now use it in almost all of our projects and infrastructure. In this talk, we’ll share our use cases and detail what we’ve learned using client-go in production. We’ll also share some best practices and show a demo to illustrate how you can get started with the client yourself. About Aaron Schlesinger Aaron Schlesinger is a Sr. Software Engineer at Deis. He leads or contributes to development on the Deis Workflow PaaS projects, Helm and the Kubernetes sig-service-catalog Kubernetes incubator project. He’s been a software developer for 10+ years, and most of that time has focused on distributed systems from large scale data warehousing to real time servers. He's a Golang developer at heart. Presentation Video: https://www.youtube.com/watch?v=wRJekZXpZC0

1. Programming Kubernetes With
the Go SDK
Aaron Schlesinger, Sr. Engineer, Deis
Co-Lead SIG-Service-Catalog

2. Today
● Use cases
● Code
● Demo
● Patterns

3. The 12 Days of Kubernetes
● The “Zen of Kubernetes”
● Basic resource types
● kubectl usage
● Helm?

4. And on the 13th Day...

5. And on the 14th Day...

6. Third Party Resources (TPR)
Ingress Controllers
Horizontal Pod Autoscalers
User Aggregated Services

7. Build your own PaaS
Trigger deployments, mutate Services, watch events, etc….

8. The core API enables powerful distributed systems primitives
Wizard Level
Coordination
Leader Election
Latches

9. switchMode(“code”)

10. Defining client-go
● k8s.io/client-go
● Focused on building clients (not a mono-repo*)
● Full access to the core API
● But wait, there’s more!
* Automatically copied from staging directory in kubernetes/kubernetes

11. k8s.io/client-go
kubernetes
rest
dynamic
pkg/api/...

12. cfg, err := rest.InClusterConfig()
...
cl, err := kubernetes.NewForConfig(cfg)
...
pods, err := cl.CoreV1().Pods(namespace).List(listOptions)
...
“Hello World”

13. The Real Deal
A program that can back up the state of (parts of) a cluster.
Backup is triggered by adding a TPR.

14. watch loop
dynamic client
watch event filterer
TPR watcher (main)
fetcher/logger

15. github.com/arschles/2017-KubeCon-EU

16. ● Build a controller to watch for events (doesn’t need to be a server)
● Be prepared for the watch stream to close at any time
● Build your own k8s resources with TPRs
● TPRs are a great way to add custom functionality
Patterns

17. Thank You!

18. github.com/arschles/2017-KubeCon-EU
github.com/kubernetes/client-go
@arschles
Questions?

19. Homework
● Support more resources
● Support modification of Backups
● Write cluster state into a new TPR (instead of logging to STDOUT)
● Write status back to the Backup TPR