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Merge pull request #29193 from sftim/20210802_improve_statefulset_minreadyseconds_docs 

Improve StatefulSet .minReadySeconds docs
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@ -228,39 +228,33 @@ and Ready or completely terminated prior to launching or terminating another
Pod. This option only affects the behavior for scaling operations. Updates are not
affected.
#### Minimum Ready Seconds
{{< feature-state for_k8s_version="v1.22" state="alpha" >}}
## Update strategies
`.spec.minReadySeconds` is an optional field that specifies the minimum number of seconds for which a newly
created Pod should be ready without any of its containers crashing, for it to be considered available.
This defaults to 0 (the Pod will be considered available as soon as it is ready). To learn more about when
a Pod is considered ready, see [Container Probes](/docs/concepts/workloads/pods/pod-lifecycle/#container-probes).
Please note that this field only works if you enable the `StatefulSetMinReadySeconds` feature gate.
## Update Strategies
In Kubernetes 1.7 and later, StatefulSet's `.spec.updateStrategy` field allows you to configure
A StatefulSet's `.spec.updateStrategy` field allows you to configure
and disable automated rolling updates for containers, labels, resource request/limits, and
annotations for the Pods in a StatefulSet.
annotations for the Pods in a StatefulSet. There are two possible values:
### On Delete
`OnDelete`
: When a StatefulSet's `.spec.updateStrategy.type` is set to `OnDelete`,
the StatefulSet controller will not automatically update the Pods in a
StatefulSet. Users must manually delete Pods to cause the controller to
create new Pods that reflect modifications made to a StatefulSet's `.spec.template`.
The `OnDelete` update strategy implements the legacy (1.6 and prior) behavior. When a StatefulSet's
`.spec.updateStrategy.type` is set to `OnDelete`, the StatefulSet controller will not automatically
update the Pods in a StatefulSet. Users must manually delete Pods to cause the controller to
create new Pods that reflect modifications made to a StatefulSet's `.spec.template`.
`RollingUpdate`
: The `RollingUpdate` update strategy implements automated, rolling update for the Pods in a StatefulSet. This is the default update strategy.
### Rolling Updates
## Rolling Updates
The `RollingUpdate` update strategy implements automated, rolling update for the Pods in a
StatefulSet. It is the default strategy when `.spec.updateStrategy` is left unspecified. When a StatefulSet's `.spec.updateStrategy.type` is set to `RollingUpdate`, the
When a StatefulSet's `.spec.updateStrategy.type` is set to `RollingUpdate`, the
StatefulSet controller will delete and recreate each Pod in the StatefulSet. It will proceed
in the same order as Pod termination (from the largest ordinal to the smallest), updating
each Pod one at a time. It will wait until an updated Pod is Running and Ready prior to
updating its predecessor.
each Pod one at a time.
#### Partitions
The Kubernetes control plane waits until an updated Pod is Running and Ready prior
to updating its predecessor. If you have set `.spec.minReadySeconds` (see [Minimum Ready Seconds](#minimum-ready-seconds)), the control plane additionally waits that amount of time after the Pod turns ready, before moving on.
### Partitioned rolling updates {#partitions}
The `RollingUpdate` update strategy can be partitioned, by specifying a
`.spec.updateStrategy.rollingUpdate.partition`. If a partition is specified, all Pods with an
@ -272,7 +266,7 @@ updates to its `.spec.template` will not be propagated to its Pods.
In most cases you will not need to use a partition, but they are useful if you want to stage an
update, roll out a canary, or perform a phased roll out.
#### Forced Rollback
### Forced rollback
When using [Rolling Updates](#rolling-updates) with the default
[Pod Management Policy](#pod-management-policies) (`OrderedReady`),
@ -292,6 +286,16 @@ After reverting the template, you must also delete any Pods that StatefulSet had
already attempted to run with the bad configuration.
StatefulSet will then begin to recreate the Pods using the reverted template.
### Minimum ready seconds
{{< feature-state for_k8s_version="v1.22" state="alpha" >}}
`.spec.minReadySeconds` is an optional field that specifies the minimum number of seconds for which a newly
created Pod should be ready without any of its containers crashing, for it to be considered available.
This defaults to 0 (the Pod will be considered available as soon as it is ready). To learn more about when
a Pod is considered ready, see [Container Probes](/docs/concepts/workloads/pods/pod-lifecycle/#container-probes).
Please note that this field only works if you enable the `StatefulSetMinReadySeconds` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/).
## {{% heading "whatsnext" %}}