mirror of https://github.com/k3s-io/k3s
80 lines
4.6 KiB
Markdown
80 lines
4.6 KiB
Markdown
## Overview
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This example shows two types of pod health checks: HTTP checks and container execution checks.
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The [exec-liveness.yaml](./exec-liveness.yaml) demonstrates the container execution check.
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```
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livenessProbe:
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exec:
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command:
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- cat
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- /tmp/health
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initialDelaySeconds: 15
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timeoutSeconds: 1
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```
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Kubelet executes the command cat /tmp/health in the container and reports failure if the command returns a non-zero exit code.
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Note that the container removes the /tmp/health file after 10 seconds,
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```
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echo ok > /tmp/health; sleep 10; rm -rf /tmp/health; sleep 600
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```
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so when Kubelet executes the health check 15 seconds (defined by initialDelaySeconds) after the container started, the check would fail.
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The [http-liveness.yaml](http-liveness.yaml) demonstrates the HTTP check.
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```
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livenessProbe:
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httpGet:
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path: /healthz
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port: 8080
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initialDelaySeconds: 15
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timeoutSeconds: 1
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```
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The Kubelet sends a HTTP request to the specified path and port to perform the health check. If you take a look at image/server.go, you will see the server starts to respond with an error code 500 after 10 seconds, so the check fails.
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This [guide](https://github.com/GoogleCloudPlatform/kubernetes/blob/master/examples/walkthrough/k8s201.md#health-checking) has more information on health checks.
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## Get your hands dirty
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To show the health check is actually working, first create the pods:
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```
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# kubectl create -f exec-liveness.yaml
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# kubectl create -f http-liveness.yaml
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```
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Check the status of the pods once they are created:
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```
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# kubectl get pods
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POD IP CONTAINER(S) IMAGE(S) HOST LABELS STATUS CREATED MESSAGE
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liveness-exec 10.244.3.7 kubernetes-minion-f08h/130.211.122.180 test=liveness Running 3 seconds
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liveness gcr.io/google_containers/busybox Running 2 seconds
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liveness-http 10.244.0.8 kubernetes-minion-0bks/104.197.10.10 test=liveness Running 3 seconds
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liveness gcr.io/google_containers/liveness Running 2 seconds
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```
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Check the status half a minute later, you will see the termination messages:
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```
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# kubectl get pods
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POD IP CONTAINER(S) IMAGE(S) HOST LABELS STATUS CREATED MESSAGE
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liveness-exec 10.244.3.7 kubernetes-minion-f08h/130.211.122.180 test=liveness Running 34 seconds
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liveness gcr.io/google_containers/busybox Running 3 seconds last termination: exit code 137
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liveness-http 10.244.0.8 kubernetes-minion-0bks/104.197.10.10 test=liveness Running 34 seconds
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liveness gcr.io/google_containers/liveness Running 13 seconds last termination: exit code 2
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```
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The termination messages indicate that the liveness probes have failed, and the containers have been killed and recreated.
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You can also see the container restart count being incremented by running `kubectl describe`.
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```
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# kubectl describe pods liveness-exec | grep "Restart Count"
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Restart Count: 8
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```
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You would also see the killing and creating events at the bottom of the *kubectl describe* output:
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```
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Thu, 14 May 2015 15:23:25 -0700 Thu, 14 May 2015 15:23:25 -0700 1 {kubelet kubernetes-minion-0uzf} spec.containers{liveness} killing Killing 88c8b717d8b0940d52743c086b43c3fad0d725a36300b9b5f0ad3a1c8cef2d3e
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Thu, 14 May 2015 15:23:25 -0700 Thu, 14 May 2015 15:23:25 -0700 1 {kubelet kubernetes-minion-0uzf} spec.containers{liveness} created Created with docker id b254a9810073f9ee9075bb38ac29a4b063647176ad9eabd9184078ca98a60062
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Thu, 14 May 2015 15:23:25 -0700 Thu, 14 May 2015 15:23:25 -0700 1 {kubelet kubernetes-minion-0uzf} spec.containers{liveness} started Started with docker id b254a9810073f9ee9075bb38ac29a4b063647176ad9eabd9184078ca98a60062
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...
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```
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[]()
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