106 lines
4.1 KiB
Markdown
106 lines
4.1 KiB
Markdown
---
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title: Federated ReplicaSets
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---
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This guide explains how to use replica sets in the Federation control plane.
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* TOC
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{:toc}
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## Prerequisites
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This guide assumes that you have a running Kubernetes Cluster
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Federation installation. If not, then head over to the
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[federation admin guide](/docs/admin/federation/) to learn how to
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bring up a cluster federation (or have your cluster administrator do
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this for you). Other tutorials, for example
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[this one](https://github.com/kelseyhightower/kubernetes-cluster-federation)
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by Kelsey Hightower, are also available to help you.
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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/user-guide/replicasets/) in particular.
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## Overview
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Replica Sets in federation control plane (referred to as "federated replica sets" in
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this guide) are very similar to the traditional [Kubernetes
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ReplicaSets](/docs/user-guide/replicasets/), 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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## Creating a Federated Replica Set
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The API for Federated Replica Set is 100% compatible with the
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API for traditional Kubernetes Replica Set. You can create a replica set 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 replica set is created, the federation control plane will create
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a replica set 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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These replica sets in underlying clusters will match the federation replica set
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except in the number of replicas. Federation control plane will ensure that the
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sum of replicas in each cluster match the desired number of replicas in the
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federation replica set.
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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 replica set with
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`spec.replicas = 9`, then each replica set 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 federated replica set.
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## Updating a Federated Replica Set
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You can update a federated replica set as you would update a Kubernetes
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replica set; however, for a federated replica set, 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 plan ensures that whenever the federated replica set is
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updated, it updates the corresponding replica sets 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 replica set.
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## Deleting a Federated Replica Set
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You can delete a federated replica set as you would delete a Kubernetes
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replica set; however, for a federated replica set, 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 replica set will not delete the
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corresponding replica sets from underlying clusters.
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You must delete the underlying Replica Sets manually.
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We intend to fix this in the future.
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