Managing Stateful Applications in Kubernetes
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The document outlines the management of stateful applications in Kubernetes, emphasizing the differences between stateful and stateless apps, and how Kubernetes can facilitate running both types. It discusses key concepts such as container orchestration, persistent volumes, and stateful sets, which are essential for maintaining data integrity and application performance. The document highlights the advantages of using Kubernetes for stateful applications, including scalability and efficient resource utilization.
Managing Stateful Applications in Kubernetes
- 1. Managing Stateful Apps In Kubernetes
- 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?
- 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!