Presented at All Things Open 2018 Presented by Rajashree Mandaogane with Rancher Labs 10/23/18 - 11:45 AM - Networking/Infrastructure Track

1. Managing Stateful Apps In
Kubernetes

3. @rajashree_28 mrajashree
I’m Rajashree

5. 1. Containers and Container Orchestration
2.Kubernetes
3.Stateless vs stateful apps
4.Running stateful apps on k8s

6. 1. Containers and Container Orchestration
2.Kubernetes
3.Stateless vs stateful apps
4.Running stateful apps on k8s

7. Containers

8. Application packaging
• Source code, dependencies, env vars
• Application portability
• Performance consistency
• No more “it works on my machine”

10. OS level virtualization
• Containers share host Operating System
• Lightweight as opposed to a VM
• One host can run multiple containers
• Resource isolation
• Increased efficiency

11. Managing containers
Container
Node
Container
Container
• Scheduling across nodes
• Availability

12. EC2
Container
EC2 EC2
Client
Managing containers
Container
Container
Container
Container
Container
Container
Container
Container
Run 3 containers
Run 3 containers
Run 3 containers

13. Managing containers
• Which machine is my container running on?
• Are there sufficient resources for my app?
• How do containers communicate with each
other?
• How do I manage load balancing?
• How do I ensure healthcheck/monitoring?

14. Container orchestration

15. Client
EC2
Container
Container
Container
EC2
Container
Container
Container
EC2
Container
Container
Container
Run 9 containers

16. 1. Containers and Container Orchestration
2.Kubernetes
3.Stateless vs stateful apps
4.Running stateful apps on k8s

17. Kubernetes!
• Manage containerized applications
• Open source
• Scalability
• Handle upgrades

18. Pod
• Smallest deployable unit
• One or more containers
• “one-container-per-pod”
• Unique IP address
Container
Pod
10.10.1.1
Node

19. Deployment
• Pods are ephemeral
• Deployments manage pod life-cycle
• Ensure actual state same as desired
• Provide easy scaling, upgrades for apps

20. k8s cluster
Pod 1
10.10.1.1
10.11.1.1
10.11.1.2
Pod 2
Pod 3
Node 1
Node 2
Deployment
selector=
app: nginx
labels=
app: nginx
labels=
app: nginx
labels=
app: nginx

21. 1. Containers and Container Orchestration
2.Kubernetes
3.Stateless vs stateful apps
4.Running stateful apps on k8s

22. Stateless
• No persisted data
• No application state
• Pods are replaceable
• Examples: edge API server, nginx

23. Stateful
• Persisted data
• Server/node identity is irreplaceable
• Examples: mysql, cassandra

24. Why run stateful apps on k8s?
1. Depends on use case
2. Leverage containerization benefits
3. Manage stateless and stateful apps together
4. Ability to use same infrastructure provider
5. Easy scalability
6. Affordability

25. 1. Containers and Container Orchestration
2.Kubernetes
3.Stateless vs stateful apps
4.Running stateful apps on k8s

26. K8s objects for statefulness
• Persistent Volumes (PV)
• Persistent Volume Claims (PVC)
• Storage Class
• StatefulSet

27. Persistent volume
• Storage resource in k8s
• Volume plugins
• Created by cluster admin
• Lifecycle independent of pod

28. Persistent Volume Claims
• Request to claim a storage resource
• Abstracts storage details of PV from user
• User only specifies size and access mode
• Access modes: RWO, RWM, ROM

29. Static Provisioning
Cluster admin
Creates PV
PV
size: 10 GB
AccessMode: RWO
User
Creates PVC
PVC
requests:
size: 3 GB (min)
AccessMode: RWO
Available
PVController
Bound

30. Limitations?
• User created PVC requesting 3 Gib
• But there was only one PV with 10 Gib
• PV got bound to PVC with excess volume
• User will get a PV-PVC binding only if admin
has created enough PVs

31. Storage Class
• Resource for classifying storage
• Specifies provisioner, parameters, reclaimPolicy
• Created by cluster admin
• User must know name of Storage Class

32. Dynamic Provisioning
Cluster admin
Creates
Storage Class
Name: standard
Provisioner: aws-ebs
Parameters: type=gp2
ReclaimPolicy: Delete
User
Creates PVC
PVC
storageClass: standard
size: 3 GB (min)
AccessMode: RWO
Creates PV
PV
size: 3 GB
AccessMode: RWO

33. Dynamic Provisioning
• Efficient resource utilization
• Only needs storageClass and PVC creation
• PV created dynamically

34. Pod in stateful app
• Stores data independently
• Should have separate PV
• Needs separate PVC for separate PV

35. • Lets say you want 10 pods for your app
• Do you create 10 PVCs?
• What about when you want to scale up?
• Can something create PVCs dynamically too?
Pod in stateful app

36. StatefulSets
• Stable unique persistent volume for each pod
• Creates PVC using a volume claim template
• Stable unique network identifier for all pods
• Ordered deployment and scaling
• Automated rolling updates

37. Use Case - Cassandra
• Highly available, scalable
• Uses replication while storing data
• All nodes are equal
• Cassandra nodes can identify each other

38. EC2 EC2
cassandra-0 cassandra-1 cassandra-2
PVC 0
PV 0 PV 1 PV 2
PVC 1 PVC 2
StatefulSet

39. 1. Containers and Container Orchestration
2.Kubernetes
3.Stateless vs stateful apps
4.Running stateful apps on k8s

40. Thank you!