I do not want to decrease the number of pods controlled by StatefulSet, and i think that decreasing pods is a dangerous operation in production env.
so... , is there some way ? thx ~
i think that decreasing pods is a dangerous operation in production env.
I agree with you.
As Crou wrote, it is possible to do this operation with kubectl scale statefulsets <stateful-set-name>
but this is an imperative operation and it is not recommended to do imperative operations in a production environment.
In a production environment it is better to use a declarative operation, e.g. have the number of replicas in a text file (e.g. stateful-set-name.yaml) and deploy them with kubectl apply -f <stateful-set-name>.yaml
with this way of working, it is easy to store the yaml-files in Git so you have full control of all changes and can revert/rollback to a previous configuration. When you store the declarative files in a Git repository you can use a CICD solution e.g. Jenkins or ArgoCD to 1) validate the operation (e.g. not allow decrease) and 2) first deploy to a test-environment and see that it works, before applying the changes to the production environment.
I recommend the book (new edition) Kubernetes Up&Running 2nd ed that describes this procedure in Chapter 18 (new chapter).
I'm not sure if this is what you are looking for but you can scale a StatefulSet
Use kubectl to scale StatefulSets
First, find the StatefulSet you want to scale.
kubectl get statefulsets <stateful-set-name>
Change the number of replicas of your StatefulSet:
kubectl scale statefulsets <stateful-set-name> --replicas=<new-replicas>
To show you an example, I've deployed a 2 pod StatefulSet called web
:
$ kubectl get statefulsets.apps web
NAME READY AGE
web 2/2 60s
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
web-0 1/1 Running 0 63s
web-1 1/1 Running 0 44s
$ kubectl describe statefulsets.apps web
Name: web
Namespace: default
CreationTimestamp: Wed, 23 Oct 2019 13:46:33 +0200
Selector: app=nginx
Labels: <none>
Annotations: kubectl.kubernetes.io/last-applied-configuration:
{"apiVersion":"apps/v1","kind":"StatefulSet","metadata":{"annotations":{},"name":"web","namespace":"default"},"spec":{"replicas":2,"select...
Replicas: 824643442664 desired | 2 total
Update Strategy: RollingUpdate
Partition: 824643442984
Pods Status: 2 Running / 0 Waiting / 0 Succeeded / 0 Failed
...
Now if we do scale this StatefulSet up to 5 replicas:
$ kubectl scale statefulset web --replicas=5
statefulset.apps/web scaled
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
web-0 1/1 Running 0 3m41s
web-1 1/1 Running 0 3m22s
web-2 1/1 Running 0 59s
web-3 1/1 Running 0 40s
web-4 1/1 Running 0 27s
$ kubectl get statefulsets.apps web
NAME READY AGE
web 5/5 3m56s
You do not have any downtime in already working pods.