In Kubernetes, how to set pods' names when using replication controllers? - kubernetes

Question

I have a simple replication controller yaml file which looks like this:
apiVersion: v1
kind: ReplicationController
metadata:
name: nginx
spec:
replicas: 3
selector:
app: nginx
template:
spec:
containers:
- image: library/nginx:3.2
imagePullPolicy: IfNotPresent
name: nginx
ports:
- containerPort: 80
metadata:
labels:
app: nginx
And after running this replication controller, I will get 3 different pods whose names are "nginx-xxx", where "xxx" represents a random string of letters and digits.
What I want is to specify names for the pods created by the replication controller, so that the pods' name can be "nginx-01", "nginx-02", "nginx-03". And further more, for say if pod "nginx-02" is down for some reason, and replication controller will automatically create another nginx pod, and I want this new nginx pod's name to remain as "nginx-02".
I wonder if this is possible? Thanks in advance.

Answer 1

You should be using statefulset instead of replication controllers. Moreover, replication controllers are replaced with ReplicaSets.
StatefulSet Pods have a unique identity that is comprised of an ordinal. For a StatefulSet with N replicas, each Pod in the StatefulSet will be assigned an integer ordinal, from 0 up through N-1, that is unique over the Set. Each Pod in a StatefulSet derives its hostname from the name of the StatefulSet and the ordinal of the Pod.
StatefulSets matches your requirements and hence use it in your deployment.
Try the deployment files below:
apiVersion: v1
kind: Service
metadata:
name: nginx
labels:
app: nginx
spec:
ports:
- port: 80
name: web
clusterIP: None
selector:
app: nginx
---
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:
terminationGracePeriodSeconds: 10
containers:
- name: nginx
image: k8s.gcr.io/nginx-slim:0.8
ports:
- containerPort: 80
name: web
volumeMounts:
- name: www
mountPath: /usr/share/nginx/html
volumes:
- name: www
emptyDir:

Answer 2

This can be implemented using statefulsets which is out of beta since version 1.9. Quoting the documentation: When using kind: StatefulSet,
Pods have a unique identity that is comprised of an ordinal, a stable network identity, and stable storage. The identity sticks to the Pod, regardless of which node it’s (re)scheduled on.
Each Pod in a StatefulSet derives its hostname from the name of the StatefulSet and the ordinal of the Pod. The pattern for the constructed hostname is $(statefulset name)-$(ordinal).
So in the example above, you would get nginx-0,nginx-1,nginx-2

Answer 3

If you're running stateless workloads, I cannot imagine why you would want to have fixed identities associated with each object if your intention is to run N replicas of a particular pod.
There is no way to do this using a ReplicaSet/ReplicationController. When the controller creates new pods, it will have a generated name suffix after the pod name.
If that is what you really want (fixed identity/ordinal index), the property is satisfied by the StatefulSet resource which is stable since Kubernetes v1.9. However, it also comes with additional guarantees that you probably do not need.