95 lines
2.9 KiB
Markdown
95 lines
2.9 KiB
Markdown
---
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title: Attaching Handlers to Container Lifecycle Events
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---
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{% capture overview %}
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This page shows how to attach handlers to Container lifecycle events. Kubernetes supports
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the postStart and preStop events. Kubernetes sends the postStart event immediately
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after a Container is started, and it sends the preStop event immediately before the
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Container is terminated.
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{% endcapture %}
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{% capture prerequisites %}
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{% include task-tutorial-prereqs.md %}
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{% endcapture %}
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{% capture steps %}
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## Defining postStart and preStop handlers
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In this exercise, you create a Pod that has one Container. The Container has handlers
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for the postStart and preStop events.
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Here is the configuration file for the Pod:
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{% include code.html language="yaml" file="lifecycle-events.yaml" ghlink="/docs/tasks/configure-pod-container/lifecycle-events.yaml" %}
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In the configuration file, you can see that the postStart command writes a `message`
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file to the Container's `/usr/share` directory. The preStop command shuts down
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nginx gracefully. This is helpful if the Container is being terminated because of a failure.
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Create the Pod:
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kubectl create -f http://k8s.io/docs/tasks/configure-pod-container/lifecycle-events.yaml
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Verify that the Container in the Pod is running:
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kubectl get pod lifecycle-demo
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Get a shell into the Container running in your Pod:
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kubectl exec -it lifecycle-demo -- /bin/bash
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In your shell, verify that the `postStart` handler created the `message` file:
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root@lifecycle-demo:/# cat /usr/share/message
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The output shows the text written by the postStart handler:
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Hello from the postStart handler
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{% endcapture %}
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{% capture discussion %}
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## Discussion
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Kubernetes sends the postStart event immediately after the Container is created.
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There is no guarantee, however, that the postStart handler is called before
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the Container's entrypoint is called. The postStart handler runs asynchronously
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relative to the Container's code, but Kubernetes' management of the container
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blocks until the postStart handler completes. The Container's status is not
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set to RUNNING until the postStart handler completes.
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Kubernetes sends the preStop event immediately before the Container is terminated.
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Kubernetes' management of the Container blocks until the preStop handler completes,
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unless the Pod's grace period expires. For more details, see
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[Termination of Pods](/docs/user-guide/pods/#termination-of-pods).
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{% endcapture %}
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{% capture whatsnext %}
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* Learn more about [Container lifecycle hooks](/docs/user-guide/container-environment/.)
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* Learn more about the [lifecycle of a Pod](https://kubernetes.io/docs/user-guide/pod-states/).
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### Reference
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* [Lifecycle](https://kubernetes.io/docs/resources-reference/1_5/#lifecycle-v1)
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* [Container](https://kubernetes.io/docs/resources-reference/1_5/#container-v1)
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* See `terminationGracePeriodSeconds` in [PodSpec](/docs/resources-reference/v1.5/#podspec-v1)
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{% endcapture %}
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{% include templates/task.md %}
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