Updated April 13, 2023
Introduction to Kubernetes StatefulSet
The Kubernetes statefulset is defined as the statefulset is a device that assists us to install and manage the group of Kubernetes pods we can say that the statefulset is the feature which is provided by Kubernetes in which it has installation options for running a container and it gives guarantee regarding the ordering and uniqueness of the pod such as deployment. It controls pods that are based on similar container spec, the pods in the Kubernetes are installed in consecutive order and that are terminated in opposite ordinal order, if the statefulset has web then its pods are named as web0, web1, and web2.
What is Kubernetes Statefulset?
The statefulset in Kubernetes is a device that can be used to control and it can able carry one or more pods, the statefulset applications are used and that does not care about which network is using and that also does not want the lasing storage because the statefulset applications may require the web servers, we have also need to know that every pod in the statefulset has ordinal values and steady network ID which can be used for allocation, if a pod has been implemented by statefulset then that comes in an order form which is started from 0(zero) and up to the final pod hence the pod will run steady and they get ready previous to the new pod has been created.
Using Kubernetes Statefulset
The statefulset outlined to implement the stateful applications and the statefulset applications are useful for applications,
- Steady and has unique network identifiers in which we can say that the stateful applications are useful for such type of application.o It is useful for application which is steady and has persistent storage.
- The statefulset is useful when we have ordered applications with elegant implementation and scaling.
- The statefulset is also useful when applications are ordered with automated rolling updates.
How to Create a statefulset?
We can able to create or generate the statefulset by using the kubectl apply, in which the statefulset can spontaneously take the place of the pod and spontaneously connect to the new pod with storage assets and those assets are requests and limits, the statefulset can be arranged by using a manifest file.
Example
Let us see an example of statefulset in which it can first generate the headless service ‘mgynx’ to print the IP addresses of the pod.
Code:
apiVersion: v2
kind: Service
metadata:
name: mgynx
label:
appli: mgynx
spec:
ports:
- port: 70
name: web
clusterIP: None
selector:
appli: mgynx
---
apiVersion: apps/v2
kind: StatefulSet
metadata:
name: web
spec:
serviceName: "mgynx"
replicas: 2
selector:
matchLabels:
appli: mgynx
template:
metadata:
labels:
appli: mgynx
spec:
containers:
- name: mgynx
pic: k7m.gcr.io/mginx-slem:0.7
ports:
- containerPort: 70
name: brow
volumeMounts:
- name: www
mountPath: /user/share/mgynx/html
volumeClaimTemplates:
- metadata:
name: www
spec:
accessMode: [ "ReadOnlyMany" ]
resource:
requests:
storage: 2GiIn the above example, we have two terminals in first we have created a headless service and we have used ‘kubectl get’ for creating the pod in statefulset such as below,
'kubectl get pods -w -l appli= mgynx'In the second terminal, we have used ‘kubectl apply’ for creating headless service and for defining the statefulset on the web.YAML,
'kubectl apply -f web. yaml'By using this command we can able to generate two pods running on the server.
When we run the command ‘kubectl get service mgynx’ then it will give the services which are related to server mgynx and when we run the command ‘kubectl get statefulset web’ then it will show the statefulset which are created successfully.
Pods in a statefulset
The pods in the statefulset have one special ordinal index and one stable network identity,
- Ordinal index:
We can get the pods in statefulset by using the below command,
'kubectl get pods -l appli=mgynx'As we have seen in statefulset the pods can have the sticky and special identity which can be related to the special ordinal number and we can allocate them to each pod in statefulset, if the statefulset has two replicas then it generates the two webs as web-0 and web-1.
- Network identity:
Every pod has a steady hostname which can be based on their ordinal index number ‘kubectl exec’ command has been used to execute the hostname
- ‘fori in 0 1; do kubectl exec “web-$i” — sh -c ‘hostname’; done’, this command will provide the web-0 and web-1 simultaneously.
- The ‘kubectl run’ command has been used to execute the container.
- We can use the ‘kubectl delete’ command for deleting the pod in statefulset.
Kubernetes statefulset limitations
It has some limitations for statefulset in Kubernetes, in which if
- The repository for a given pod in Kubernetes should be equipped with a persistent volume equipper which depends on the seek storage class by the admin.
- If we remove or ascend the statefulset downward then that will not able to remove the volume which is correlated with the statefulset, that can be settled for safety of data which is more helpful than the automatic removal of all statefulset assets.
- Right now, the statefulset has a headless service that is accountable for the network identity of a pod.
- The statefulset does not give the assurance on the closing of the pod if the pod has been removed, to carry off the ordered and graceful conclusion of the pod if a statefulset is deleted then we can able to scale the statefulset down to 0 for removing.
o When we use the rolling updates with the help of pod management policy it is attainable to obtain a shattered state that can be repaired manually.
Conclusion
In this article we have concluded that the statefulset in Kubernetes has been used to control the statefulset applications in which it gives the guarantee of ordering and uniqueness, we have discussed that how to use the statefulset, how to create it, limitations and also seen how to create the statefulset in Kubernetes.
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