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Proposal for deploy in kubectl
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Janet Kuo
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docs/proposals/deploy.md
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docs/proposals/deploy.md
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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<h2>PLEASE NOTE: This document applies to the HEAD of the source tree</h2>
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If you are using a released version of Kubernetes, you should
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refer to the docs that go with that version.
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<strong>
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The latest release of this document can be found
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[here](http://releases.k8s.io/release-1.1/docs/proposals/deploy.md).
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Documentation for other releases can be found at
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[releases.k8s.io](http://releases.k8s.io).
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</strong>
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--
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<!-- BEGIN MUNGE: GENERATED_TOC -->
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- [Deploy through CLI](#deploy-through-cli)
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- [Motivation](#motivation)
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- [Requirements](#requirements)
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- [Related `kubectl` Commands](#related-kubectl-commands)
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- [`kubectl run`](#kubectl-run)
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- [`kubectl scale` and `kubectl autoscale`](#kubectl-scale-and-kubectl-autoscale)
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- [`kubectl rollout`](#kubectl-rollout)
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- [`kubectl set`](#kubectl-set)
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- [Example](#example)
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- [Support in Deployment](#support-in-deployment)
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- [Deployment Status](#deployment-status)
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- [Deployment Version](#deployment-version)
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- [Inert Deployments](#inert-deployments)
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- [Perm-failed Deployments](#perm-failed-deployments)
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<!-- END MUNGE: GENERATED_TOC -->
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# Deploy through CLI
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## Motivation
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Users can use Deployments or `kubectl rolling-update` to deploy in their Kubernetes clusters. A Deployment provides declarative update for Pods and ReplicationControllers, whereas `rolling-update` allows the users to update their earlier deployment without worrying about schemas and configurations. Users need a way that's similar to `rolling-update` to manage their Deployments more easily.
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`rolling-update` expects ReplicationController as the only resource type it deals with. It's not trivial to support exactly the same behavior with Deployment, which requires:
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- Print out scaling up/down events.
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- Stop the deployment if users press Ctrl-c.
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- The controller should not make any more changes once the process ends. (Delete the deployment when status.replicas=status.updatedReplicas=spec.replicas)
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So, instead, this document proposes another way to support easier deployment management via Kubernetes CLI (`kubectl`).
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## Requirements
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The followings are operations we need to support for the users to easily managing deployments:
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- **Create**: To create deployments.
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- **Rollback**: To restore to an earlier version of deployment.
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- **Watch the status**: To watch for the status update of deployments.
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- **Pause/resume**: To pause a deployment mid-way, and to resume it. (A use case is to support canary deployment.)
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- **Version information**: To record and show version information that's meaningful to users. This can be useful for rollback.
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## Related `kubectl` Commands
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### `kubectl run`
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`kubectl run` should support the creation of Deployment (already implemented) and DaemonSet resources.
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### `kubectl scale` and `kubectl autoscale`
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Users may use `kubectl scale` or `kubectl autoscale` to scale up and down Deployments (both already implemented).
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### `kubectl rollout`
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`kubectl rollout` supports both Deployment and DaemonSet. It has the following subcommands:
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- `kubectl rollout undo` works like rollback; it allows the users to rollback to a previous version of deployment.
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- `kubectl rollout pause` allows the users to pause a deployment.
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- `kubectl rollout resume` allows the users to resume a paused deployment.
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- `kubectl rollout status` shows the status of a deployment.
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- `kubectl rollout history` shows meaningful version information of all previous deployments.
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### `kubectl set`
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`kubectl set` has the following subcommands:
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- `kubectl set env` allows the users to set environment variables of Kubernetes resources. It should support Pod, ReplicationController, ReplicaSet, Deployment, and DaemonSet.
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- `kubectl set image` allows the users to update the image of deployments. Users will use `--container` and `--image` flags to update the image of a container.
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### Example
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With the commands introduced above, here's an example of deployment management:
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```console
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# Create a Deployment
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$ kubectl run nginx --image=nginx --replicas=2 --generator=deployment/v1beta1
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# Watch the Deployment status
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$ kubectl rollout status deployment/nginx
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# Update the Deployment
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$ kubectl set image deployment/nginx --container=nginx --image=nginx:<some-version>
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# Pause the Deployment
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$ kubectl rollout pause deployment/nginx
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# Resume the Deployment
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$ kubectl rollout resume deployment/nginx
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# Check the change history (deployment versions)
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$ kubectl rollout history deployment/nginx
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# Rollback to a previous version.
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$ kubectl rollout undo deployment/nginx --to-version=<version>
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```
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## Support in Deployment
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### Deployment Status
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Deployment status should summarize information about Pods, which includes:
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- The number of pods of each version.
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- The number of ready/not ready pods.
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See issue [#17164](https://github.com/kubernetes/kubernetes/issues/17164).
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### Deployment Version
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We store previous deployment versions information in deployment annotation `kubectl.kubernetes.io/deployment-version-<time>`. The value stored in the annotation can be a spec hash, a strategic merge patch or the kubectl commands previously executed. We choose strategic merge patch since it's more human-readable than spec hash, and commands like `kubectl edit` won't provide enough useful information.
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### Inert Deployments
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Users sometimes need to temporarily disable a deployment. See issue [#14516](https://github.com/kubernetes/kubernetes/issues/14516).
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### Perm-failed Deployments
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The deployment could be marked as "permanently failed" for a given spec hash so that the system won't continue thrashing on a doomed deployment. See issue [#14519](https://github.com/kubernetes/kubernetes/issues/14519).
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[]()
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