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title: Ciclos de Vida do Contêiner
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content_type: concept
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weight: 30
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---
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<!-- overview -->
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Essa página descreve como os contêineres gerenciados pelo _kubelet_ podem usar a estrutura de _hook_ de ciclo de vida do contêiner para executar código acionado por eventos durante seu ciclo de vida de gerenciamento.
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<!-- body -->
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## Visão Geral
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Análogo a muitas estruturas de linguagem de programação que tem _hooks_ de ciclo de vida de componentes, como angular,
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o Kubernetes fornece aos contêineres _hooks_ de ciclo de vida.
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Os _hooks_ permitem que os contêineres estejam cientes dos eventos em seu ciclo de vida de gerenciamento
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e executem código implementado em um manipulador quando o _hook_ de ciclo de vida correspondente é executado.
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## Hooks do contêiner
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Existem dois _hooks_ que são expostos para os contêiners:
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`PostStart`
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This hook is executed immediately after a container is created.
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However, there is no guarantee that the hook will execute before the container ENTRYPOINT.
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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
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event such as a liveness/startup probe failure, preemption, resource contention and others. A call
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to the `PreStop` hook fails if the container is already in a terminated or completed state and the
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hook must complete before the TERM signal to stop the container can be sent. The Pod's termination
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grace period countdown begins before the `PreStop` hook is executed, so regardless of the outcome of
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the handler, the container will eventually terminate within the Pod's termination grace period. No
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parameters are 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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### Hook handler implementations
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Containers can access a hook by implementing and registering a handler for that hook.
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There are two types of hook handlers that can be implemented for Containers:
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* Exec - Executes a specific command, such as `pre-stop.sh`, inside the cgroups and namespaces of the Container.
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Resources consumed by the command are counted against the Container.
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* HTTP - Executes an HTTP request against a specific endpoint on the Container.
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### Hook handler execution
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When a Container lifecycle management hook is called,
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the Kubernetes management system execute the handler according to the hook action,
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`httpGet` and `tcpSocket` are executed by the kubelet process, and `exec` is executed in the container.
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Hook handler calls are synchronous within the context of the Pod containing the Container.
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This means that for a `PostStart` hook,
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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 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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Users should make their hook handlers as lightweight as possible.
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There are cases, however, when long running commands make sense,
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such as when saving state prior to stopping a Container.
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### Hook delivery guarantees
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Hook delivery is intended to be *at least once*,
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which means that a hook may be called multiple times for any given event,
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such as for `PostStart` or `PreStop`.
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It is up to the hook implementation to handle this correctly.
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Generally, only single deliveries are made.
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If, for example, an HTTP hook receiver is down and is unable to take traffic,
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there is no attempt to resend.
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In some rare cases, however, double delivery may occur.
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For instance, if a kubelet restarts in the middle of sending a hook,
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the hook might be resent after the kubelet comes back up.
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### Debugging Hook handlers
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The logs for a Hook handler are not exposed in Pod events.
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If a handler fails for some reason, it broadcasts an event.
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For `PostStart`, this is the `FailedPostStartHook` event,
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and for `PreStop`, this is the `FailedPreStopHook` event.
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You can see these events by running `kubectl describe pod <pod_name>`.
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Here is some example output of events from running this command:
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```
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Events:
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FirstSeen LastSeen Count From SubObjectPath Type Reason Message
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--------- -------- ----- ---- ------------- -------- ------ -------
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1m 1m 1 {default-scheduler } Normal Scheduled Successfully assigned test-1730497541-cq1d2 to gke-test-cluster-default-pool-a07e5d30-siqd
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1m 1m 1 {kubelet gke-test-cluster-default-pool-a07e5d30-siqd} spec.containers{main} Normal Pulling pulling image "test:1.0"
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1m 1m 1 {kubelet gke-test-cluster-default-pool-a07e5d30-siqd} spec.containers{main} Normal Created Created container with docker id 5c6a256a2567; Security:[seccomp=unconfined]
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1m 1m 1 {kubelet gke-test-cluster-default-pool-a07e5d30-siqd} spec.containers{main} Normal Pulled Successfully pulled image "test:1.0"
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1m 1m 1 {kubelet gke-test-cluster-default-pool-a07e5d30-siqd} spec.containers{main} Normal Started Started container with docker id 5c6a256a2567
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38s 38s 1 {kubelet gke-test-cluster-default-pool-a07e5d30-siqd} spec.containers{main} Normal Killing Killing container with docker id 5c6a256a2567: PostStart handler: Error executing in Docker Container: 1
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37s 37s 1 {kubelet gke-test-cluster-default-pool-a07e5d30-siqd} spec.containers{main} Normal Killing Killing container with docker id 8df9fdfd7054: PostStart handler: Error executing in Docker Container: 1
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38s 37s 2 {kubelet gke-test-cluster-default-pool-a07e5d30-siqd} Warning FailedSync Error syncing pod, skipping: failed to "StartContainer" for "main" with RunContainerError: "PostStart handler: Error executing in Docker Container: 1"
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1m 22s 2 {kubelet gke-test-cluster-default-pool-a07e5d30-siqd} spec.containers{main} Warning FailedPostStartHook
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```
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## {{% heading "whatsnext" %}}
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* Learn more about the [Container environment](/docs/concepts/containers/container-environment/).
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* Get hands-on experience
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[attaching handlers to Container lifecycle events](/docs/tasks/configure-pod-container/attach-handler-lifecycle-event/).
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