StatefulSet

Krishna & Dhilip Huawei India

February 25th 2017

Agenda Why StatefulSet Stateful application in the Cloud Stateful Vs Stateless Cloud Native/Micro Service Volumes in Statefulset Use Case

Single Instance Stateful Application Multiple Instance Stateful Application

Demo of Stateful Application Deployment Future Roadmap References

Why stateful set?

Deployments and ReplicaSets are a great way to run stateless replicas of an application. Stateless containers like web servers - so-called “cattle” because they are interchangeable, users are increasingly deploying stateful workloads with containers to benefit from “build once, run anywhere”

These “pets” - so-called because each requires special handling - bring new requirements including longer life cycle, configuration dependencies, stateful failover, and performance sensitivity.

Pet Set sequences through the startup phase of each database replica (for example), ensuring orderly master/slave configuration.

Pet Set also simplifies service discovery by leveraging ubiquitous DNS SRV records, a well-recognized and long-understood mechanism.

1.3. Kubernetes support for stateful apps called pet set and 1.5 renamed it to stateful set - Name change plus “at most one pod per index”, ordered deployment, ordered termination, unique network names, and persistent stable storage.

Stateful vs. Stateless

Volumes in statefulsetKubernetes to manage the stateless tiers of your ecosystem, you should consider using the same infrastructure to manage your storage applications.Kubernetes doesn’t yet support isolation for network or storage I/O across containers. Colocating your storage application with a noisy neighbor can reduce the QPS that your application can handle.

•emptyDir•hostPath•gcePersistentDisk•awsElasticBlockStore•Nfs•Iscsi•Flocker•Glusterfs•Rbd•gitRepo•Secret•persistentVolumeClaim

CloudNative / MicroservicesCloud native not necessary 12 factor(Heroku way of doing) Microservices is and architecture not necessarily cloud

nativeWorkload could be data streaming instead of web.Cloud Native is a set of patterns? (e.g: Cloud Foundry is one

of the patterns)OCI is for standards but CNCF is or projects, tools, APIsGo is not necessary the language. Any language is OK. E.g:

Linkerd – is JVMCloudnative need not be containers only. Unikernals and

functions can be different.Special purpose dev environment is serverless, it can be

cloud native or not. Netflix OSS is JVM based

.

Running a Single-Instance Stateful Application

Running a Multi-Instance Stateful Applicatione.g:#1Zookeeper is an interesting use case for StatefulSet for two reasons. First, it demonstrates that StatefulSet can be used to run a distributed, strongly consistent storage application on Kubernetes. Second, it's a prerequisite for running workloads like Apache Hadoop and Apache Kakfa on Kubernetes. An in-depth tutorial on deploying a ZooKeeper ensemble on Kubernetes is available in the Kubernetes documentation, and we’ll outline a few of the key features below.

e.g:#2

DEMO – Redis Service in K8s (20 min.)

Current Status Was originally proposed as PetSet Became Statefulset from 1.5, you could

migrate Petset to statefulset now Re-written recently. Ordered/Sequenced Starting of PODs are

going to be relaxed. New Annotation Debug Annotation will be removed. More Focus on Stability More charts are converted to Statefulset

Statefulset and Friends Always needs additional Kubernetes entities to

make it work very well Service - Mandatory Initcontainers PodDisruptionBudget Interpod Anti-affinity / Anti-Affinity ConfigMaps

Future roadmap Support well defined upgrade Support arbitery field update Statefulset in federated clusters Statefulset compatible with shard based

application / legacy applications. A good Cleanup mechanism GC leftover PODs, leftover PVC and Services

References

•https://www.linkedin.com/pulse/strategies-running-stateful-applications-kubernetes-volumes-msv•http://slides.com/wallnerryan/key-concepts-for-stateful-services-in-kubernetes#•http://blog.kubernetes.io/2016/12/statefulset-run-scale-stateful-applications-in-kubernetes.html•https://thenewstack.io/strategies-running-stateful-applications-kubernetes-pet-sets/•https://clusterhq.com/2016/04/11/kubecon-microservices-kai/

Some contents in this presentation are taken from the references above. Thx to authors for the posting

Thank You