ReplicaSet selector
- Docker & Kubernetes course
- Intermediate
- Lesson 33/82
- 4 min
Learn to match Pods with ReplicaSet selector.
ReplicaSet selector
A ReplicaSet owns pods by their labels, not by their names. If a pod matching the selector and without an owner is created by hand, the ReplicaSet counts it too and deletes one because there are too many. That is why labels should be chosen to be unique across workloads.
selector:
matchExpressions:
- key: app
operator: In
values: [api]
- key: katman
operator: NotIn
values: [test]Detaching a pod from a ReplicaSet
If you change a pod's label, it no longer matches the selector; the ReplicaSet lets it go and opens a new one in its place. It's a handy technique for taking a problem pod out of traffic and the ReplicaSet to inspect it without deleting it:
kubectl label pod api-5d8f7c9b4-qrstu app=inceleme --overwrite
kubectl get pods --show-labels
# api-5d8f7c9b4-qrstu app=inceleme <- detached
# api-5d8f7c9b4-zzzzz app=api <- opened in its placePractice Detach and inspect a pod
Write three commands: overwrite the app label of the api-5d8f7c9b4-qrstu pod with inceleme; list the pods with their labels; show the logs of the detached pod.
Starter code
# buraya yazSample solution
kubectl label pod api-5d8f7c9b4-qrstu app=inceleme --overwrite
kubectl get pods --show-labels
kubectl logs api-5d8f7c9b4-qrstuExpected output
pod/api-5d8f7c9b4-qrstu labeled NAME READY STATUS LABELS api-5d8f7c9b4-qrstu 1/1 Running app=inceleme,pod-template-hash=5d8f7c9b4 api-5d8f7c9b4-zzzzz 1/1 Running app=api,pod-template-hash=5d8f7c9b4 ERROR veritabanı zaman aşımı
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What happens if you create by hand a pod matching a 3-replica ReplicaSet's selector?
- It errors
- The ReplicaSet sees 4 pods and deletes one Correct answer
- The pod is ignored
- The ReplicaSet switches to 4 replicas
Explanation: A ReplicaSet adopts matching pods that have no owner.
2 Overwrite an existing label.
kubectl label pod api-5d8f7c9b4-qrstu app=inceleme ____kubectl label pod api-5d8f7c9b4-qrstu app=inceleme --overwriteExplanation: --overwrite is needed to change an existing key.
3 Match the operators.
| Term | Meaning |
|---|---|
In |
One of the values |
NotIn |
None of the values |
Exists |
Key exists |
DoesNotExist |
Key missing |