Add task page: Update a Deployment Without Downtime

Update content/en/docs/tasks/run-application/update-deployment-rolling.md

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Update content/en/docs/tasks/run-application/update-deployment-rolling.md

Co-authored-by: Tim Bannister <193443691+lmktfy@users.noreply.github.com>

Update content/en/docs/tasks/run-application/update-deployment-rolling.md

Co-authored-by: Tim Bannister <193443691+lmktfy@users.noreply.github.com>

Update content/en/docs/tasks/run-application/update-deployment-rolling.md

Co-authored-by: Tim Bannister <193443691+lmktfy@users.noreply.github.com>

Update content/en/docs/tasks/run-application/update-deployment-rolling.md

Co-authored-by: Tim Bannister <193443691+lmktfy@users.noreply.github.com>

Author: Caesarsage

content/en/docs/tasks/run-application/run-stateless-application-deployment.md

@@ -162,3 +162,4 @@ added to Kubernetes, replicated applications were configured using a
 ## {{% heading "whatsnext" %}}
 
 - Learn more about [Deployment objects](/docs/concepts/workloads/controllers/deployment/).
+- Learn how to [update a Deployment without downtime](/docs/tasks/run-application/update-deployment-rolling/).

content/en/docs/tasks/run-application/update-deployment-rolling.md

@@ -0,0 +1,313 @@
+---
+title: Update a Deployment Without Downtime
+content_type: task
+weight: 16
+---
+
+<!-- overview -->
+
+This page shows how to update a running Deployment to a new version using a
+rolling update. A rolling update gradually replaces old Pods with new ones, so
+your application remains available throughout the process.
+
+## {{% heading "objectives" %}}
+
+- Trigger a rolling update on a Deployment.
+- Monitor rollout progress.
+- Pause and resume the rollout.
+- Configure rolling update strategy parameters.
+- (If required) Roll back to a previous revision.
+
+## {{% heading "prerequisites" %}}
+
+{{< include "task-tutorial-prereqs.md" >}}
+
+You need an existing Deployment. If you do not have one, create the nginx
+Deployment from
+[Run a Stateless Application Using a Deployment](/docs/tasks/run-application/run-stateless-application-deployment/):
+
+```shell
+kubectl apply -f https://k8s.io/examples/application/deployment.yaml
+```
+
+Verify the Deployment runs two Pods:
+
+```shell
+kubectl get deployment nginx-deployment
+```
+
+The output is similar to:
+
+```
+NAME               READY   UP-TO-DATE   AVAILABLE   AGE
+nginx-deployment   2/2     2            2           10s
+```
+
+<!-- steps -->
+
+## Performing a rolling update
+
+Any change to the `.spec.template` field of a Deployment triggers a rolling
+update. Kubernetes creates new Pods with the updated configuration and gradually
+terminates old Pods.
+
+### Updating with `kubectl apply`
+
+You can trigger a rolling update by editing the Deployment manifest and applying the change. This approach works well when you keep manifests in version control.
+
+Export the current Deployment to a local file:
+
+```shell
+kubectl get deployment nginx-deployment -o yaml > /tmp/nginx-deployment.yaml
+```
+
+Edit `/tmp/nginx-deployment.yaml` and change `.spec.template.spec.containers[0].image`
+from `nginx:1.14.2` to `nginx:1.16.1`.
+
+Before applying, compare your local changes against the cluster state:
+
+```shell
+kubectl diff -f /tmp/nginx-deployment.yaml
+```
+
+The output is similar to:
+
+```
+diff -u -N /tmp/LIVE/apps.v1.Deployment.default.nginx-deployment /tmp/MERGED/apps.v1.Deployment.default.nginx-deployment
+--- /tmp/LIVE/apps.v1.Deployment...
++++ /tmp/MERGED/apps.v1.Deployment...
+@@ -29,7 +29,7 @@
+       containers:
+-      - image: nginx:1.14.2
++      - image: nginx:1.16.1
+         name: nginx
+```
+
+Apply the updated manifest:
+
+```shell
+kubectl apply -f /tmp/nginx-deployment.yaml
+```
+
+### Updating only the container image
+
+To update the container image without editing a manifest file, use
+`kubectl set image`:
+
+```shell
+kubectl set image deployment/nginx-deployment nginx=nginx:1.16.1
+```
+
+The output is similar to:
+
+```
+deployment.apps/nginx-deployment image updated
+```
+
+Verify the image was updated:
+
+```shell
+kubectl get deployment nginx-deployment -o jsonpath='{.spec.template.spec.containers[0].image}'
+```
+
+The output is similar to:
+
+```
+nginx:1.16.1
+```
+
+## Monitoring rollout progress
+
+Use `kubectl rollout status` to watch the progress of a rolling update:
+
+```shell
+kubectl rollout status deployment/nginx-deployment
+```
+
+The output is similar to:
+
+```
+Waiting for deployment "nginx-deployment" rollout to finish: 1 out of 2 new replicas have been updated...
+Waiting for deployment "nginx-deployment" rollout to finish: 1 out of 2 new replicas have been updated...
+Waiting for deployment "nginx-deployment" rollout to finish: 1 old replicas are pending termination...
+deployment "nginx-deployment" successfully rolled out
+```
+
+After the rollout completes, verify the Deployment:
+
+```shell
+kubectl get deployment nginx-deployment
+```
+
+The output is similar to:
+
+```
+NAME               READY   UP-TO-DATE   AVAILABLE   AGE
+nginx-deployment   2/2     2            2           2m
+```
+
+## Pausing and resuming a rollout
+
+You can pause a rollout to inspect a partial update or to batch multiple changes
+into a single rollout.
+
+### Pausing a rollout
+
+```shell
+kubectl rollout pause deployment/nginx-deployment
+```
+
+The output is similar to:
+
+```
+deployment.apps/nginx-deployment paused
+```
+
+### Making additional changes while paused
+
+While the rollout is paused, you can make additional changes. These changes do
+not trigger a new rollout until you resume:
+
+```shell
+kubectl set image deployment/nginx-deployment nginx=nginx:1.17.0
+```
+
+{{< note >}}
+You can make multiple changes to a paused Deployment. Kubernetes applies all
+changes together when you resume the rollout.
+{{< /note >}}
+
+### Resuming a rollout
+
+```shell
+kubectl rollout resume deployment/nginx-deployment
+```
+
+The output is similar to:
+
+```
+deployment.apps/nginx-deployment resumed
+```
+
+Verify the rollout completes:
+
+```shell
+kubectl rollout status deployment/nginx-deployment
+```
+
+## Configuring rolling update strategy
+
+Deployments support two
+[update strategy types](/docs/concepts/workloads/controllers/deployment/#strategy):
+
+- **RollingUpdate** (default): gradually replaces old Pods with new ones.
+- **Recreate**: terminates all existing Pods before creating new ones. This
+  causes downtime.
+
+For the RollingUpdate strategy, these parameters control how Kubernetes performs the update:
+
+| Parameter | Controls | Default | Example |
+|-----------|----------|---------|---------|
+| `maxUnavailable` | Maximum number of Pods that can be unavailable during the update | 25% | `1` or `25%` |
+| `maxSurge` | Maximum number of extra Pods that can be created during the update | 25% | `1` or `25%` |
+
+{{< note >}}
+`maxUnavailable` and `maxSurge` accept an absolute number or a percentage.
+Kubernetes calculates percentages from the desired replica count, rounding down
+for `maxUnavailable` and rounding up for `maxSurge`.
+{{< /note >}}
+
+To configure these parameters, use `kubectl patch`:
+
+```shell
+kubectl patch deployment nginx-deployment -p \
+  '{"spec":{"strategy":{"rollingUpdate":{"maxUnavailable":"25%","maxSurge":"25%"}}}}'
+```
+
+You can also set these fields in a Deployment manifest under
+`.spec.strategy.rollingUpdate`. For detailed examples, see
+[max unavailable](/docs/concepts/workloads/controllers/deployment/#max-unavailable)
+and [max surge](/docs/concepts/workloads/controllers/deployment/#max-surge)
+in the Deployment concepts documentation.
+
+### Detecting a stalled rollout
+
+If a rollout does not make progress within the time specified by
+`.spec.progressDeadlineSeconds` (default: 600 seconds), Kubernetes marks the Deployment condition `Progressing` as `False`. You can check for this condition by describing the Deployment:
+
+```shell
+kubectl describe deployment nginx-deployment
+```
+
+Look for the `Progressing` condition in the `Conditions` section of the output. A stalled rollout usually indicates that new Pods are failing to start. The `Events` section of the output can help diagnose the issue.
+
+## Rolling back to a previous revision {#rollback}
+
+If a new version introduces issues, you can roll back to a previous revision.
+
+### Viewing rollout history
+
+```shell
+kubectl rollout history deployment/nginx-deployment
+```
+
+The output is similar to:
+
+```
+deployment.apps/nginx-deployment
+REVISION  CHANGE-CAUSE
+1         <none>
+2         <none>
+```
+
+{{< note >}}
+The `CHANGE-CAUSE` column shows the value of the `kubernetes.io/change-cause`
+annotation at the time of each revision. This annotation is **not** set automatically,
+but if you are using an automated solution to manage Deployments, the tool you use
+may write some text into that annotation.
+{{< /note >}}
+
+### Rolling back to the previous revision
+
+```shell
+kubectl rollout undo deployment/nginx-deployment
+```
+
+The output is similar to:
+
+```
+deployment.apps/nginx-deployment rolled back
+```
+
+### Rolling back to a specific revision
+
+```shell
+kubectl rollout undo deployment/nginx-deployment --to-revision=1
+```
+
+Verify the rollback completes:
+
+```shell
+kubectl rollout status deployment/nginx-deployment
+```
+
+{{< note >}}
+A Deployment's revision history is stored in the ReplicaSets it controls.
+By default, Kubernetes retains 10 old ReplicaSets. You can change this limit
+by setting `.spec.revisionHistoryLimit` in the Deployment manifest. Setting it to `0` disables rollback entirely.
+{{< /note >}}
+
+## {{% heading "cleanup" %}}
+
+Delete the Deployment:
+
+```shell
+kubectl delete deployment nginx-deployment
+```
+
+## {{% heading "whatsnext" %}}
+
+- Learn more about [Deployments](/docs/concepts/workloads/controllers/deployment/).
+- Learn how to [scale a Deployment manually](/docs/tasks/run-application/scale-deployment/).
+- Walk through [Horizontal Pod Autoscaling](/docs/tasks/run-application/horizontal-pod-autoscale-walkthrough/).
+- See how to [perform a rolling update on a DaemonSet](/docs/tasks/manage-daemon/update-daemon-set/).