ReplicaSet（RS）是Replication Controller（RC）的升级版本。ReplicaSet 和 Replication Controller之间的唯一区别是对选择器的支持。ReplicaSet支持labels user guide中描述的set-based选择器要求， 而Replication Controller仅支持equality-based的选择器要求。
如何使用ReplicaSet
大多数kubectl 支持Replication Controller 命令的也支持ReplicaSets。rolling-update命令除外，如果要使用rolling-update，请使用Deployments来实现。
虽然ReplicaSets可以独立使用，但它主要被 Deployments用作pod 机制的创建、删除和更新。当使用Deployment时，你不必担心创建pod的ReplicaSets，因为可以通过Deployment实现管理ReplicaSets。
何时使用ReplicaSet
ReplicaSet能确保运行指定数量的pod。然而，Deployment 是一个更高层次的概念，它能管理ReplicaSets，并提供对pod的更新等功能。因此，我们建议你使用Deployment来管理ReplicaSets，除非你需要自定义更新编排。
这意味着你可能永远不需要操作ReplicaSet对象，而是使用Deployment替代管理 。
示例
apiVersion: extensions/v1beta1
kind: ReplicaSet
metadata:
name: frontend
# these labels can be applied automatically
# from the labels in the pod template if not set
# labels:
# app: guestbook
# tier: frontend
spec:
# this replicas value is default
# modify it according to your case
replicas: 3
# selector can be applied automatically
# from the labels in the pod template if not set,
# but we are specifying the selector here to
# demonstrate its usage.
selector:
matchLabels:
tier: frontend
matchExpressions:
- {key: tier, operator: In, values: [frontend]}
template:
metadata:
labels:
app: guestbook
tier: frontend
spec:
containers:
- name: php-redis
image: gcr.io/google_samples/gb-frontend:v3
resources:
requests:
cpu: 100m
memory: 100Mi
env:
- name: GET_HOSTS_FROM
value: dns
# If your cluster config does not include a dns service, then to
# instead access environment variables to find service host
# info, comment out the 'value: dns' line above, and uncomment the
# line below.
# value: env
ports:
- containerPort: 80
将此配置保存到（frontend.yaml）并提交到Kubernetes集群时，将创建定义的ReplicaSet及其管理的pod。
$ kubectl create -f frontend.yaml
replicaset "frontend" created
$ kubectl describe rs/frontend
Name: frontend
Namespace: default
Image(s): gcr.io/google_samples/gb-frontend:v3
Selector: tier=frontend,tier in (frontend)
Labels: app=guestbook,tier=frontend
Replicas: 3 current / 3 desired
Pods Status: 3 Running / 0 Waiting / 0 Succeeded / 0 Failed
No volumes.
Events:
FirstSeen LastSeen Count From SubobjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ -------
1m 1m 1 {replicaset-controller } Normal SuccessfulCreate Created pod: frontend-qhloh
1m 1m 1 {replicaset-controller } Normal SuccessfulCreate Created pod: frontend-dnjpy
1m 1m 1 {replicaset-controller } Normal SuccessfulCreate Created pod: frontend-9si5l
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
frontend-9si5l 1/1 Running 0 1m
frontend-dnjpy 1/1 Running 0 1m
frontend-qhloh 1/1 Running 0 1m
ReplicaSet as an Horizontal Pod Autoscaler target
ReplicaSet也可以作为 Horizontal Pod Autoscalers (HPA)的目标 。也就是说，一个ReplicaSet可以由一个HPA来自动伸缩。以下是针对我们在上一个示例中创建的ReplicaSet的HPA示例。
hpa-rs.yaml  |
|---|
apiVersion: autoscaling/v1
kind: HorizontalPodAutoscaler
metadata:
name: frontend-scaler
spec:
scaleTargetRef:
kind: ReplicaSet
name: frontend
minReplicas: 3
maxReplicas: 10
targetCPUUtilizationPercentage: 50
|
kubectl create -f hpa-rs.yaml