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explain Available condition behavior in deployment concepts #39892

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explain Available condition behavior in deployment concepts #39892

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19 changes: 17 additions & 2 deletions content/en/docs/concepts/workloads/controllers/deployment.md
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Expand Up @@ -1027,8 +1027,23 @@ Conditions:
Progressing True NewReplicaSetAvailable
```

`type: Available` with `status: "True"` means that your Deployment has minimum availability. Minimum availability is dictated
by the parameters specified in the deployment strategy. `type: Progressing` with `status: "True"` means that your Deployment
`type: Available` with `status: "True"` means that your Deployment is healthy and has a minimum availability (`.status.availableReplicas` is at least equal to `.spec.replicas - maxUnavailable`).
`maxUnavailable` is computed according to the deployment strategy:
- For the `RollingUpdate` strategy, it is a resolved value of `.spec.strategy.rollingUpdate.maxUnavailable`.
- For the `Recreate` strategy, it is always equal to 100% of the replicas that we allow to be down, so that new rollouts can proceed.
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This counts with a change proposed in kubernetes/kubernetes#113228. Currently it is 0.


This condition should always have `status: "True"` in day-to-day operations; during and also after a rollout is completed.
The condition will become `status: "False"` if there is an abnormal amount of disrupted pods (higher than a resolved value of `maxUnavailable`).

{{< note >}}
The `Available` condition is designed to support rollouts first. If `maxUnavailable` is equal to `.spec.replicas`,
then this condition will never become `status: "False"`, even if no pods are running.
In this case you should check `.status.availableReplicas` to be sure that at least 1 pod is present.
It is recommended to have the number of `.spec.replicas` higher than `maxUnavailable`, to have always some pods available during a rollout.
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Good description!

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Thanks. I suppose we will wait with this PR until we are all satisfied with the changes in kubernetes/kubernetes#113228

{{< /note >}}


`type: Progressing` with `status: "True"` means that your Deployment
is either in the middle of a rollout and it is progressing or that it has successfully completed its progress and the minimum
required new replicas are available (see the Reason of the condition for the particulars - in our case
`reason: NewReplicaSetAvailable` means that the Deployment is complete).
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