1.9 KiB
1.9 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 manigest 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?
Exercises
Nothing to see here.
Clean up
kubectl delete statefulset,deployment,service,pod --all