Stateful Applications mit Kubernetes

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STATEFUL APPLICATIONS MIT KUBERNETES BED-CON 2017 Nicolas Byl, codecentric AG 1

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PERSISTENT APPLICATION STATE 3 . 1

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GOALS Scalable Highly Available Fault Tolerance 3 . 2

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EXAMPLE ARCHITECTURE 3 . 3

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CANDIDATES MySQL PostgreSQL Cassandra MongoDB Kafka … 3 . 4

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KUBERNETES 4 . 1

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DESIGN PHILOSOPHY portable: public, private, hybrid, multi-cloud extensible: modular, pluggable, hookable, composable self-healing: auto-placement, auto-restart, auto-replication, auto-scaling 4 . 2

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PODS 4 . 3

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SERVICES 4 . 4

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PERSISTENT VOLUMES 5 . 1

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5 . 2

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GCEPersistentDisk CephFS AWSElasticBlockStore Cinder (OpenStack block storage) AzureFile Glusterfs AzureDisk VsphereVolume FC (Fibre Channel) Quobyte Volumes FlexVolume HostPath Flocker VMware Photon

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NFS vPortworx Volumes iSCSI ScaleIO Volumes RBD (Ceph Block Device) StorageOS 5 . 3

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ACCESS MODES ReadWriteOnce – the volume can be mounted as read-write by a single node ReadOnlyMany – the volume can be mounted read-only by many nodes ReadWriteMany – the volume can be mounted as read-write by many nodes 5 . 4

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USAGE Provision Disk Create Persistent Volume Create Persistent Volume Claim Mount Claim in Pod 5 . 5

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PERSISTENT VOLUME apiVersion: v1 kind: PersistentVolume metadata: name: pv0003 spec: capacity: storage: 5Gi accessModes: - ReadWriteOnce persistentVolumeReclaimPolicy: Recycle nfs: path: /tmp server: 172.17.0.2 5 . 6

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PERSISTENT VOLUME CLAIM kind: PersistentVolumeClaim apiVersion: v1 metadata: name: myclaim spec: accessModes: - ReadWriteOnce resources: requests: storage: 8Gi 5 . 7

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MOUNTING A PVC kind: Pod apiVersion: v1 metadata: name: mypod spec: containers: - name: mydatabase image: mysql:5.7 volumeMounts: - mountPath: "/var/lib/mysql" name: mypd volumes: - name: mypd persistentVolumeClaim: claimName: myclaim 5 . 8

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COMMON PITFALLS The abstraction is leaky. Local storage vs. SAN storage vs. Network Filesystems 5 . 9

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AUTO-PROVISIONING 6 . 1

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AUTO-PROVISIONING Manual creation of Persistent Volumes is error-prone. Does not scale well. 6 . 2

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STORAGECLASS kind: StorageClass apiVersion: storage.k8s.io/v1 metadata: name: standard provisioner: kubernetes.io/aws-ebs parameters: type: gp2 6 . 3

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USING A STORAGECLASS kind: PersistentVolumeClaim apiVersion: v1 metadata: name: myclaim spec: accessModes: - ReadWriteOnce resources: requests: storage: 8Gi storageClassName: standard 6 . 4

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SUPPORTED PROVISIONERS default volume plugins (in-tree provisioners) out-of-tree provisioners community provisioners: write your own: https://github.com/kubernetes- incubator/external-storage https://github.com/kubernetes- incubator/external- storage/tree/master/docs/demo/hostpath-provisioner 6 . 5

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SCALING 7 . 1

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ARCHITECTURE REVISITED 7 . 2

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SHARING PVCS Need different paths per Pod. Share needs to be available on every host. Corruption of file system affects all database nodes. Sharing a Persistent Volume Claim is not a good idea. 7 . 3

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STATEFUL SETS 8 . 1

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STATEFULSETS Pod template mechanism Hostnames are atomically increased: pod-0 pod-1 … Volume Claims can be provisioned on-the-fly 8 . 2

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STATEFULSET EXAMPLE apiVersion: apps/v1beta1 kind: StatefulSet metadata: name: web spec: serviceName: "nginx" replicas: 2 template: metadata: labels: app: nginx spec: containers: - name: nginx image: gcr.io/google_containers/nginx-slim:0.8 ports: - containerPort: 80 name: web volumeMounts: 8 . 3

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ARCHITECTURE STATEFULSETS 8 . 4

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WRAP UP 9 . 1

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LINKS Persistent Volumes: Tutorial StatefulSet: Demos: https://kubernetes.io/docs/concepts/storage/persistent- volumes https://kubernetes.io/docs/tutorials/stateful-application/basic- stateful-set/ https://goo.gl/NCnzq8 9 . 2