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Document the safe-to-evict annotation on the webhook deployment #3961

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May 22, 2021
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Document the safe-to-evict annotation on the webhook deployment #3961

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4 changes: 4 additions & 0 deletions docs/enabling-ha.md
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Expand Up @@ -88,6 +88,10 @@ spec:
minReplicas: 1
```

By default, the Webhook deployment is configured to block a [Cluster Autoscaler](https://github.com/kubernetes/autoscaler/tree/master/cluster-autoscaler) from scaling down the node that's running the only replica of the deployment using the `cluster-autoscaler.kubernetes.io/safe-to-evict` annotation.
This is configured because, while the only replica of the Webhook is unavailable, Tekton resources can't be created, updated or deleted.
If you configure more than one replica, you can remove the annotation to allow the Cluster Autoscaler more freedom to scale down nodes, without disrupting the Webhook service.

### Avoiding Disruptions

To avoid the Webhook Service becoming unavailable during node unavailability (e.g., during node upgrades), you can ensure that a minimum number of Webhook replicas are available at time by defining a [`PodDisruptionBudget`](https://kubernetes.io/docs/tasks/run-application/configure-pdb/) which sets a `minAvailable` greater than zero:
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