Clarify PreStop hook behaviour
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2527359c13
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content/en/docs/concepts/containers
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@ -36,10 +36,12 @@ No parameters are passed to the handler.
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`PreStop`
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This hook is called immediately before a container is terminated due to an API request or management event such as liveness probe failure, preemption, resource contention and others. A call to the preStop hook fails if the container is already in terminated or completed state.
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It is blocking, meaning it is synchronous,
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so it must complete before the signal to stop the container can be sent.
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No parameters are passed to the handler.
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This hook is called immediately before a container is terminated due to an API request or management
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event such as a liveness/startup probe failure, preemption, resource contention and others. This
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hook is not called if the container crashes or exits. The Pod's termination grace period countdown
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begins before the `PreStop` hook is executed. Regardless of the outcome of the handler, the
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container will eventually terminate within the Pod's termination grace period. No parameters are
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passed to the handler.
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A more detailed description of the termination behavior can be found in
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[Termination of Pods](/docs/concepts/workloads/pods/pod-lifecycle/#pod-termination).
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@ -65,19 +67,15 @@ the Container ENTRYPOINT and hook fire asynchronously.
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However, if the hook takes too long to run or hangs,
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the Container cannot reach a `running` state.
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`PreStop` hooks are not executed asynchronously from the signal
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to stop the Container; the hook must complete its execution before
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the signal can be sent.
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If a `PreStop` hook hangs during execution,
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the Pod's phase will be `Terminating` and remain there until the Pod is
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killed after its `terminationGracePeriodSeconds` expires.
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This grace period applies to the total time it takes for both
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the `PreStop` hook to execute and for the Container to stop normally.
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If, for example, `terminationGracePeriodSeconds` is 60, and the hook
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takes 55 seconds to complete, and the Container takes 10 seconds to stop
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normally after receiving the signal, then the Container will be killed
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before it can stop normally, since `terminationGracePeriodSeconds` is
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less than the total time (55+10) it takes for these two things to happen.
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`PreStop` hooks are not executed asynchronously from the signal to stop the Container; the hook must
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complete its execution before the TERM signal can be sent. If a `PreStop` hook hangs during
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execution, the Pod's phase will be `Terminating` and remain there until the Pod is killed after its
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`terminationGracePeriodSeconds` expires. This grace period applies to the total time it takes for
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both the `PreStop` hook to execute and for the Container to stop normally. If, for example,
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`terminationGracePeriodSeconds` is 60, and the hook takes 55 seconds to complete, and the Container
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takes 10 seconds to stop normally after receiving the signal, then the Container will be killed
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before it can stop normally, since `terminationGracePeriodSeconds` is less than the total time
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(55+10) it takes for these two things to happen.
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If either a `PostStart` or `PreStop` hook fails,
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it kills the Container.
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