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1.8 KiB
1.8 KiB
Stateful Sets
Introduction
Like a Deployment, a StatefulSet manages Pods that are based on an identical container spec. Unlike a Deployment, a StatefulSet maintains a sticky identity for each the pods. These are created from the same spec, but are not interchangeable: each has a persistent identifier that it maintains across any rescheduling.
StatefulSets are valuable for applications that require one or more of the following.
- Stable, unique network identifiers, ex: distributed system, like ElasticSearch
- Stable, persistent storage, ex: MySQL
- Ordered, graceful deployment and scaling
- Ordered, automated rolling updates, ex: MySQL Master+Slave
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: web
spec:
selector:
matchLabels:
app: nginx # has to match .spec.template.metadata.labels
serviceName: "nginx"
replicas: 3 # by default is 1
template:
metadata:
labels:
app: nginx # has to match .spec.selector.matchLabels
spec:
containers:
- name: nginx
image: k8s.gcr.io/nginx-slim:0.8
ports:
- containerPort: 80
name: web
volumeMounts:
- name: www
mountPath: /usr/share/nginx/html
volumeClaimTemplates:
- metadata:
name: www
spec:
accessModes: [ "ReadWriteOnce" ]
resources:
requests:
storage: 1Gi
As you can see the manifest is very close to the one of a deployment. Apply the manifest 01-statefulset.yml.
Look at the pods generated, see how they are generated. Connect to one of the pods:
kubectl exec -ti web-0 /bin/bash
Write a file in the volume www. Terminate the same pod. See what happens. Reconnect to the pod, look at volume www. What can you see?
Clean up
kubectl delete statefulset,deployment,service,pod --all