This document introduces Kubernetes operators and discusses how they can automate operations for stateful applications running on Kubernetes clusters. It explains that operators use custom resource definitions (CRDs) and custom controllers to make stateful applications declarative and enable automating tasks like backups, upgrades, and data redistribution. The operator pattern works by having a controller watch for the desired state defined by CRDs and take actions to maintain that state. The document demonstrates how operators can add new functionality to Kubernetes clusters and operate as "SRE as a service." It also introduces the Operator Framework for easily building new operators with the Operator SDK.

1. Kubernetes Operators
Introduction to
Ofir Makmal | CTO | SELA Group

2. Ku·ber·ne·tes
Kubernetes can be many things… Its a scalable, self-healing and resilient
● Container orchestration engine
● Cluster management system
● Mesos, Swarm, Rancher, _______ replacement
● Microservices, CI/CD, Machine Learning platforms
● Portable ‘cloud’
But, It’s NOT just another way to run containers...

3. In just three years time…
Recent surveys from medium & large US-based companies shows that over 60%
are currently using Kubernetes to run workloads
● Trials/POC stages through development to production stages
It has a huge community:
● ~36K Stars
● ~1600 Contributors!
● ~13K Forks
● ~1000 Pending pull requests!

5. We all know
Kubernetes
Building Blocks

6. And we all know how to run a stateless service...
Creating a Namespace, defining a Deployment to manage a
ReplicaSet of Pods, exposing them as Services and Ingress, maybe
mounting Persistent Volumes into their containers, injecting
ConfigMaps and Secrets as environment variables.
After deployment, we expect that Kubernetes will take care the rest.

7. What about stateful applications?

8. Stateless is easy, stateful is hard
i.e - Cassandra, a Distributed Database.
After deployment, comes operations.
● Backups and Restore
● Upgrades
● Auto-scaling
● Redistribution of data when cluster size changes
● Leader election in case of failure and preserving a Quorum
These kind of stateful applications are usually used as a dependency for other
stateless applications, and needed to be discovered and consumed.

9. Custom Resource Definition (CRD)
“A resource is an endpoint in the Kubernetes API that stores a collection of API
objects of a certain kind. For example, the built-in pods resource contains a
collection of Pod objects.”
*Prior to K8S 1.7 this feature was called Third Party Resource (TPR)
First class citizens in Kubernetes API and Command Line Interface
$ kubectl get CassandraClusters
$ kubectl get CassandraBackups

10. apiVersion: cassandra.d/v1alpha1
kind: CassandraCluster
metadata:
name: cassandracluster
spec:
statefulsetName: cassandracluster
replicas: 4
apiVersion: krallistic.github.com/v1
kind: KafkaCluster
metadata:
name: orders-kafka
spec:
brokerCount: 3
topics:
- name: newOrdersTopic
replicationFactor: 1
partitions: 1

11. Custom Controller
● A controller interprets the CRD data as user’s desired state
● Then, it continually takes action to achieve and maintain this state.
● Custom Resources combined with a custom controller becomes a true
declarative API
“Make sure we have X instances on different machines”
“Make sure we’ll do backup every X minutes”
“Make sure to re-distribute keys between nodes in case of X event”

12. = OperatorController + CRD

13. An Operator
● Is used for adding new kind of functionality to a Kubernetes Cluster
● Can Automates administration and operations
○ Upgrades, Backups, Reshuffling data, etc..
● Using a declarative approach - it’s not a script!
● Kube-Controller-Manager does this exactly for the native building blocks
○ Deployment, ReplicaSets, Pod, Service, etc..
○ Theres a job title exactly for that.
Site Reliability Engineer (SRE) as a service ®

14. The Operator Pattern
Observe
Watches CustomResource
state using Kubernetes API
Act
Create a plan to transition
from Current State to
Desired State
Analyze
Compare Current State to
Desired State
03
01 02

15. The Operator Pattern
for {
currentState := kubernetesApi.getCurrentState()
desiredState := kubernetesApi.getDesiredState()
takeMeThere(currentState, desiredState)
}

16. Api Server
Cassandra
Operator
KubeCTL CLI

17. Api Server
CloudSQL
Operator
KubeCTL CLI
Provision

18. Demo

19. Operator Framework by CoreOS
● Consists on:
● Operator Lifecycle Manager
● Operator Metering (Soon)
● Operator SDK
● Use Operator SDK to easily create new Operators
● Code Generated CRD’s and Custom Controller
● Using Go
● https://github.com/operator-framework

20. Stateful applications requires domain-specific
operation knowledge that needs to be automated
________
CRDs and Operator Framework opens whole new
ways for writing apps natively on top of Kubernetes

21. Thank you
Get with OfirM@Sela.co.il