Move Guide topic Replica Sets. (#3180)
Steve Perry
GitHub
parent
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@ -28,6 +28,7 @@ toc:
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- docs/concepts/workloads/pods/init-containers.md
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- title: Controllers
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section:
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- docs/concepts/workloads/controllers/replicaset.md
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- docs/concepts/workloads/controllers/deployment.md
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- docs/concepts/workloads/controllers/statefulset.md
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- docs/concepts/workloads/controllers/petset.md
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@ -0,0 +1,45 @@
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apiVersion: extensions/v1beta1
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kind: ReplicaSet
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metadata:
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name: frontend
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# these labels can be applied automatically
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# from the labels in the pod template if not set
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# labels:
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# app: guestbook
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# tier: frontend
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spec:
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# this replicas value is default
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# modify it according to your case
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replicas: 3
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# selector can be applied automatically
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# from the labels in the pod template if not set,
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# but we are specifying the selector here to
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# demonstrate its usage.
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selector:
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matchLabels:
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tier: frontend
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matchExpressions:
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- {key: tier, operator: In, values: [frontend]}
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template:
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metadata:
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labels:
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app: guestbook
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tier: frontend
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spec:
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containers:
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- name: php-redis
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image: gcr.io/google_samples/gb-frontend:v3
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resources:
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requests:
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cpu: 100m
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memory: 100Mi
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env:
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- name: GET_HOSTS_FROM
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value: dns
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# If your cluster config does not include a dns service, then to
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# instead access environment variables to find service host
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# info, comment out the 'value: dns' line above, and uncomment the
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# line below.
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# value: env
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ports:
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- containerPort: 80
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@ -0,0 +1,11 @@
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apiVersion: autoscaling/v1
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kind: HorizontalPodAutoscaler
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metadata:
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name: frontend-scaler
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spec:
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scaleTargetRef:
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kind: ReplicaSet
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name: frontend
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minReplicas: 3
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maxReplicas: 10
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targetCPUUtilizationPercentage: 50
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@ -0,0 +1,102 @@
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---
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assignees:
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- Kashomon
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- bprashanth
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- madhusudancs
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title: Replica Sets
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---
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* TOC
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{:toc}
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## What is a ReplicaSet?
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ReplicaSet is the next-generation Replication Controller. The only difference
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between a _ReplicaSet_ and a
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[_Replication Controller_](/docs/user-guide/replication-controller/) right now is
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the selector support. ReplicaSet supports the new set-based selector requirements
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as described in the [labels user guide](/docs/user-guide/labels/#label-selectors)
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whereas a Replication Controller only supports equality-based selector requirements.
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Most [`kubectl`](/docs/user-guide/kubectl/) commands that support
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Replication Controllers also support ReplicaSets. One exception is the
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[`rolling-update`](/docs/user-guide/kubectl/kubectl_rolling-update/) command. If
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you want the rolling update functionality please consider using Deployments
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instead. Also, the
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[`rolling-update`](/docs/user-guide/kubectl/kubectl_rolling-update/) command is
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imperative whereas Deployments are declarative, so we recommend using Deployments
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through the [`rollout`](/docs/user-guide/kubectl/kubectl_rollout/) command.
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While ReplicaSets can be used independently, today it's mainly used by
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[Deployments](/docs/user-guide/deployments/) as a mechanism to orchestrate pod
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creation, deletion and updates. When you use Deployments you don't have to worry
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about managing the ReplicaSets that they create. Deployments own and manage
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their ReplicaSets.
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## When to use a ReplicaSet?
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A ReplicaSet ensures that a specified number of pod “replicas” are running at any given
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time. However, a Deployment is a higher-level concept that manages ReplicaSets and
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provides declarative updates to pods along with a lot of other useful features.
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Therefore, we recommend using Deployments instead of directly using ReplicaSets, unless
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you require custom update orchestration or don't require updates at all.
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This actually means that you may never need to manipulate ReplicaSet objects:
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use directly a Deployment and define your application in the spec section.
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## Example
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{% include code.html language="yaml" file="frontend.yaml" ghlink="/docs/concepts/workloads/controllers/frontend.yaml" %}
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Saving this config into `frontend.yaml` and submitting it to a Kubernetes cluster should
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create the defined ReplicaSet and the pods that it manages.
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```shell
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$ kubectl create -f frontend.yaml
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replicaset "frontend" created
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$ kubectl describe rs/frontend
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Name: frontend
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Namespace: default
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Image(s): gcr.io/google_samples/gb-frontend:v3
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Selector: tier=frontend,tier in (frontend)
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Labels: app=guestbook,tier=frontend
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Replicas: 3 current / 3 desired
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Pods Status: 3 Running / 0 Waiting / 0 Succeeded / 0 Failed
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No volumes.
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Events:
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FirstSeen LastSeen Count From SubobjectPath Type Reason Message
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--------- -------- ----- ---- ------------- -------- ------ -------
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1m 1m 1 {replicaset-controller } Normal SuccessfulCreate Created pod: frontend-qhloh
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1m 1m 1 {replicaset-controller } Normal SuccessfulCreate Created pod: frontend-dnjpy
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1m 1m 1 {replicaset-controller } Normal SuccessfulCreate Created pod: frontend-9si5l
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$ kubectl get pods
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NAME READY STATUS RESTARTS AGE
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frontend-9si5l 1/1 Running 0 1m
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frontend-dnjpy 1/1 Running 0 1m
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frontend-qhloh 1/1 Running 0 1m
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```
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## ReplicaSet as an Horizontal Pod Autoscaler target
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A ReplicaSet can also be a target for
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[Horizontal Pod Autoscalers (HPA)](/docs/user-guide/horizontal-pod-autoscaling/),
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i.e. a ReplicaSet can be auto-scaled by an HPA. Here is an example HPA targeting
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the ReplicaSet we created in the previous example.
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{% include code.html language="yaml" file="hpa-rs.yaml" ghlink="/docs/concepts/workloads/controllers/hpa-rs.yaml" %}
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Saving this config into `hpa-rs.yaml` and submitting it to a Kubernetes cluster should
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create the defined HPA that autoscales the target ReplicaSet depending on the CPU usage
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of the replicated pods.
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```shell
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kubectl create -f hpa-rs.yaml
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```
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Alternatively, you can just use the `kubectl autoscale` command to accomplish the same
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(and it's easier!)
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```shell
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kubectl autoscale rs frontend
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```
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@ -6,97 +6,6 @@ assignees:
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title: Replica Sets
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---
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* TOC
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{:toc}
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{% include user-guide-content-moved.md %}
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## What is a ReplicaSet?
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ReplicaSet is the next-generation Replication Controller. The only difference
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between a _ReplicaSet_ and a
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[_Replication Controller_](/docs/user-guide/replication-controller/) right now is
|
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the selector support. ReplicaSet supports the new set-based selector requirements
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as described in the [labels user guide](/docs/user-guide/labels/#label-selectors)
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whereas a Replication Controller only supports equality-based selector requirements.
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|
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Most [`kubectl`](/docs/user-guide/kubectl/) commands that support
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Replication Controllers also support ReplicaSets. One exception is the
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[`rolling-update`](/docs/user-guide/kubectl/kubectl_rolling-update/) command. If
|
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you want the rolling update functionality please consider using Deployments
|
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instead. Also, the
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[`rolling-update`](/docs/user-guide/kubectl/kubectl_rolling-update/) command is
|
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imperative whereas Deployments are declarative, so we recommend using Deployments
|
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through the [`rollout`](/docs/user-guide/kubectl/kubectl_rollout/) command.
|
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|
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While ReplicaSets can be used independently, today it's mainly used by
|
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[Deployments](/docs/user-guide/deployments/) as a mechanism to orchestrate pod
|
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creation, deletion and updates. When you use Deployments you don't have to worry
|
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about managing the ReplicaSets that they create. Deployments own and manage
|
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their ReplicaSets.
|
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|
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## When to use a ReplicaSet?
|
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|
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A ReplicaSet ensures that a specified number of pod “replicas” are running at any given
|
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time. However, a Deployment is a higher-level concept that manages ReplicaSets and
|
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provides declarative updates to pods along with a lot of other useful features.
|
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Therefore, we recommend using Deployments instead of directly using ReplicaSets, unless
|
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you require custom update orchestration or don't require updates at all.
|
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|
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This actually means that you may never need to manipulate ReplicaSet objects:
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use directly a Deployment and define your application in the spec section.
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## Example
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{% include code.html language="yaml" file="replicasets/frontend.yaml" ghlink="/docs/user-guide/replicasets/frontend.yaml" %}
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Saving this config into `frontend.yaml` and submitting it to a Kubernetes cluster should
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create the defined ReplicaSet and the pods that it manages.
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```shell
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$ kubectl create -f frontend.yaml
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replicaset "frontend" created
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$ kubectl describe rs/frontend
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Name: frontend
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Namespace: default
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Image(s): gcr.io/google_samples/gb-frontend:v3
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Selector: tier=frontend,tier in (frontend)
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Labels: app=guestbook,tier=frontend
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Replicas: 3 current / 3 desired
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Pods Status: 3 Running / 0 Waiting / 0 Succeeded / 0 Failed
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No volumes.
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Events:
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FirstSeen LastSeen Count From SubobjectPath Type Reason Message
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--------- -------- ----- ---- ------------- -------- ------ -------
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1m 1m 1 {replicaset-controller } Normal SuccessfulCreate Created pod: frontend-qhloh
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1m 1m 1 {replicaset-controller } Normal SuccessfulCreate Created pod: frontend-dnjpy
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1m 1m 1 {replicaset-controller } Normal SuccessfulCreate Created pod: frontend-9si5l
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$ kubectl get pods
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NAME READY STATUS RESTARTS AGE
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frontend-9si5l 1/1 Running 0 1m
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frontend-dnjpy 1/1 Running 0 1m
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frontend-qhloh 1/1 Running 0 1m
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```
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## ReplicaSet as an Horizontal Pod Autoscaler target
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A ReplicaSet can also be a target for
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[Horizontal Pod Autoscalers (HPA)](/docs/user-guide/horizontal-pod-autoscaling/),
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i.e. a ReplicaSet can be auto-scaled by an HPA. Here is an example HPA targeting
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the ReplicaSet we created in the previous example.
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{% include code.html language="yaml" file="replicasets/hpa-rs.yaml" ghlink="/docs/user-guide/replicasets/hpa-rs.yaml" %}
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Saving this config into `hpa-rs.yaml` and submitting it to a Kubernetes cluster should
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create the defined HPA that autoscales the target ReplicaSet depending on the CPU usage
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of the replicated pods.
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```shell
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kubectl create -f hpa-rs.yaml
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```
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Alternatively, you can just use the `kubectl autoscale` command to accomplish the same
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(and it's easier!)
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```shell
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kubectl autoscale rs frontend
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```
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[ReplicaSets](/docs/concepts/workloads/controllers/replicaset/)
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