Cloud native applications are commonly thought as stateless, horizontally scalable workloads that you can scale-up and down on-demand. Kubernetes, as the commodity cloud native orchestrator, was originally designed for such workloads. A lot has evolved since Kubernetes’ inception, and nowadays many of the stateful applications are migrating to Kubernetes. While not everything is perfect, more and more features are added to support complex stateful use-cases. In this session Arthur will cover the following topics: ​ - Breakdown of a stateful application - Planning a stateful application on Kubernetes - The state of Kubernetes StatefulSets, Persistent Volumes, DNS, Networking, operators and High Availability - A practical use-case and DEMO of a stateful application with Kubernetes

1. A stateful Application
Walks Into A Kubernetes Bar...
Arthur Berezin
CEO, Founder - JovianX

2. ● Kubernetes
● Kubernetes Apps
● Kubernetes Stateful Apps

3. SaaS Backend Platform

4. Your SaaS
Customers
SaaS Backend Platform
Your SaaS
Your
Application
Operations
Console
Identity
Management
Multi-Tenancy
Application
Runtime
Application
Lifecycle
Service Level
Revenue
Management
Billing

6. ● Cluster
● Master
● Nodes

7. ● App
● Deployment

8. ● Node

9. ● Node:
○ Pod
○ IP
○ Volume

10. ● Deployment
● Service

11. ● Scale

13. stateful_app:
Storage
Identity
Uniqueness
Order

14. stateful_app:
Storage
Identity
Uniqueness
Order

15. Kubernetes Storage Abstraction Provisioners:
And More...

16. ● Volumes
● PersistentVolume(pv)
Static
● Dynamic Volume Provisioning
● PersistentVolumeClaim()

17. Dynamic Storage Provisioning
PersistentVolume(pv)
Persistent Volume (PV) represents provisioned storage in the cluster
Can be backed by NFS, iSCSI, other block, etc
PV’s lifecycle is independent of the container/pod that uses it
PVs are not deleted when the Pods

18. Dynamic Storage
Provisioning
● Portable
● Self-Service
● On-Demand
● PersistentVolumeClaim
● (pvc)

19. Storage Backend
Persistent Volume
Claim
App
App
YAML

20. Storage Backend
StorageClassPersistent Volume
Claim
Match
Class
App
App
YAML

21. Storage Backend
Volume
StorageClassPersistent Volume
Claim
Provisioner
Match
Class
App
App
YAML
Create
Volume

22. Storage Backend
Volume
StorageClassPersistent Volume
Claim
Persistent Volume
Provisioner
Match
Class
App
App
YAML
Bind
Create
Volume
Create PV

23. Storage Backend
Volume
StorageClassPersistent Volume
Claim
Persistent Volume
Provisioner
Match
Class
App
App
YAML
Bind
Create
Volume
Create PV
Volume Mounted

24. apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: jovianx-pvc
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 50Gi
storageClassName: standard
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
labels:
kubernetes.io/cluster-service:
"true"
name: standard
parameters:
type: pd-standard
provisioner: kubernetes.io/gce-pd
volumeBindingMode: Immediate
Storage ClassVolume Claim
containers:
volumeMounts:
- name: jovianx-volume
mountPath: /data
volumes:
- name: jovianx-volume
persistentVolumeClaim:
claimName: jovianx-
pvc
pod
Persistent Volume Claim

25. stateful_app:
Storage
Identity
Uniqueness
Order

26. StatefulSets

27. StatefulSets
1. Stable, unique DNS network identifiers.
2. Stable, persistent storage.
3. Ordered, graceful deployment and scaling.
4. Ordered, automated rolling updates.

28. GA in Kubernetes 1.9 (Dec 16, 2017)
Controller that manages deployment and scaling of Pods
StatefulSet maintains a sticky identity for each of their Pods
Provides guarantees about ordering and uniqueness
StatefulSets

29. StatefulSet
Ordinal Index
$(statefulset name)-$(ordinal)
[arthurberezin@roadster demo]$ kubectl get StatefulSets
NAME DESIRED CURRENT AGE
web 2 2 2m
[arthurberezin@roadster demo]$ kubectl get pods
NAME READY STATUS RESTARTS
AGE
web-0 1/1 Running 0
2m
web-1 1/1 Running 0
2m
Stable Network ID
web-{0..N-1}.nginx.default.svc.cluster.local
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: web
spec:
selector:
matchLabels:
app: nginx
serviceName: "nginx"
replicas: 2
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: k8s.gcr.io/nginx-slim:0.8
ports:
- containerPort: 80

30. StatefulSet
VolumeClaimTemplates
One PersistentVolume for each pod
Re-mounted on Pod re-schedule
volumeClaimTemplates:
- metadata:
name: www
spec:
accessModes: [ "ReadWriteOnce" ]
storageClassName: "my-storage-class"
resources:
requests:
storage: 1Gi

31. Thank you.