105 lines
4.0 KiB
Markdown
105 lines
4.0 KiB
Markdown
---
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title: Federated ReplicaSets
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redirect_from:
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- "/docs/user-guide/federation/replicasets/"
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- "/docs/user-guide/federation/replicasets.html"
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---
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{% capture overview %}
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This guide explains how to use ReplicaSets in the Federation control plane.
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ReplicaSets in the federation control plane (referred to as "federated ReplicaSets" in
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this guide) are very similar to the traditional [Kubernetes
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ReplicaSets](/docs/concepts/workloads/controllers/replicaset/), and provide the same functionality.
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Creating them in the federation control plane ensures that the desired number of
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replicas exist across the registered clusters.
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{% endcapture %}
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{% capture prerequisites %}
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* {% include federated-task-tutorial-prereqs.md %}
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* You are also expected to have a basic
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[working knowledge of Kubernetes](/docs/getting-started-guides/) in
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general and [ReplicaSets](/docs/concepts/workloads/controllers/replicaset/) in particular.
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{% endcapture %}
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{% capture steps %}
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## Creating a Federated ReplicaSet
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The API for Federated ReplicaSet is 100% compatible with the
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API for traditional Kubernetes ReplicaSet. You can create a ReplicaSet by sending
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a request to the federation apiserver.
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You can do that using [kubectl](/docs/user-guide/kubectl/) by running:
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``` shell
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kubectl --context=federation-cluster create -f myrs.yaml
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```
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The '--context=federation-cluster' flag tells kubectl to submit the
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request to the Federation apiserver instead of sending it to a Kubernetes
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cluster.
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Once a federated ReplicaSet is created, the federation control plane will create
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a ReplicaSet in all underlying Kubernetes clusters.
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You can verify this by checking each of the underlying clusters, for example:
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``` shell
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kubectl --context=gce-asia-east1a get rs myrs
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```
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The above assumes that you have a context named 'gce-asia-east1a'
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configured in your client for your cluster in that zone.
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The ReplicaSets in the underlying clusters will match the federation ReplicaSet
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except in the number of replicas. The federation control plane will ensure that the
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sum of the replicas in each cluster match the desired number of replicas in the
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federation ReplicaSet.
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### Spreading Replicas in Underlying Clusters
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By default, replicas are spread equally in all the underlying clusters. For ex:
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if you have 3 registered clusters and you create a federated ReplicaSet with
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`spec.replicas = 9`, then each ReplicaSet in the 3 clusters will have
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`spec.replicas=3`.
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To modify the number of replicas in each cluster, you can specify
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[FederatedReplicaSetPreference](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/federation/apis/federation/types.go)
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as an annotation with key `federation.kubernetes.io/replica-set-preferences`
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on the federated ReplicaSet.
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## Updating a Federated ReplicaSet
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You can update a federated ReplicaSet as you would update a Kubernetes
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ReplicaSet; however, for a federated ReplicaSet, you must send the request to
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the federation apiserver instead of sending it to a specific Kubernetes cluster.
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The Federation control plane ensures that whenever the federated ReplicaSet is
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updated, it updates the corresponding ReplicaSet in all underlying clusters to
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match it.
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If your update includes a change in number of replicas, the federation
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control plane will change the number of replicas in underlying clusters to
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ensure that their sum remains equal to the number of desired replicas in
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federated ReplicaSet.
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## Deleting a Federated ReplicaSet
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You can delete a federated ReplicaSet as you would delete a Kubernetes
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ReplicaSet; however, for a federated ReplicaSet, you must send the request to
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the federation apiserver instead of sending it to a specific Kubernetes cluster.
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For example, you can do that using kubectl by running:
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```shell
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kubectl --context=federation-cluster delete rs myrs
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```
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Note that at this point, deleting a federated ReplicaSet will not delete the
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corresponding ReplicaSets from underlying clusters.
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You must delete the underlying ReplicaSets manually.
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We intend to fix this in the future.
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{% endcapture %}
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{% include templates/task.md %}
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