k3s/docs/user-guide/liveness/README.md

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<h2>PLEASE NOTE: This document applies to the HEAD of the source tree</h2>

If you are using a released version of Kubernetes, you should
refer to the docs that go with that version.

<strong>
The latest 1.0.x release of this document can be found
[here](http://releases.k8s.io/release-1.0/docs/user-guide/liveness/README.md).

Documentation for other releases can be found at
[releases.k8s.io](http://releases.k8s.io).
</strong>
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## Overview

This example shows two types of pod [health checks](../production-pods.md#liveness-and-readiness-probes-aka-health-checks): HTTP checks and container execution checks.

The [exec-liveness.yaml](exec-liveness.yaml) demonstrates the container execution check.

```yaml
    livenessProbe:
      exec:
        command:
        - cat
        - /tmp/health
      initialDelaySeconds: 15
      timeoutSeconds: 1
```

Kubelet executes the command `cat /tmp/health` in the container and reports failure if the command returns a non-zero exit code.

Note that the container removes the `/tmp/health` file after 10 seconds,

```sh
echo ok > /tmp/health; sleep 10; rm -rf /tmp/health; sleep 600
```

so when Kubelet executes the health check 15 seconds (defined by initialDelaySeconds) after the container started, the check would fail.


The [http-liveness.yaml](http-liveness.yaml) demonstrates the HTTP check.

```yaml
    livenessProbe:
      httpGet:
        path: /healthz
        port: 8080
      initialDelaySeconds: 15
      timeoutSeconds: 1
```

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.

This [guide](../walkthrough/k8s201.md#health-checking) has more information on health checks.

## Get your hands dirty

To show the health check is actually working, first create the pods:

```console
$ kubectl create -f docs/user-guide/liveness/exec-liveness.yaml
$ kubectl create -f docs/user-guide/liveness/http-liveness.yaml
```

Check the status of the pods once they are created:

```console
$ kubectl get pods
NAME                                           READY     STATUS       RESTARTS   AGE
[...]
liveness-exec                                  1/1       Running      0          13s
liveness-http                                  1/1       Running      0          13s
```

Check the status half a minute later, you will see the container restart count being incremented:

```console
$ kubectl get pods
mwielgus@mwielgusd:~/test/k2/kubernetes/examples/liveness$ kubectl get pods
NAME                                           READY     STATUS       RESTARTS   AGE
[...]
liveness-exec                                  1/1       Running      1          36s
liveness-http                                  1/1       Running      1          36s
```

At the bottom of the *kubectl describe* output there are messages indicating that the liveness probes have failed, and the containers have been killed and recreated.

```console
$ kubectl describe pods liveness-exec
[...]
Sat, 27 Jun 2015 13:43:03 +0200    Sat, 27 Jun 2015 13:44:34 +0200    4    {kubelet kubernetes-minion-6fbi}    spec.containers{liveness}    unhealthy  Liveness probe failed: cat: can't open '/tmp/health': No such file or directory
Sat, 27 Jun 2015 13:44:44 +0200    Sat, 27 Jun 2015 13:44:44 +0200    1    {kubelet kubernetes-minion-6fbi}    spec.containers{liveness}    killing    Killing with docker id 65b52d62c635
Sat, 27 Jun 2015 13:44:44 +0200    Sat, 27 Jun 2015 13:44:44 +0200    1    {kubelet kubernetes-minion-6fbi}    spec.containers{liveness}    created    Created with docker id ed6bb004ee10
Sat, 27 Jun 2015 13:44:44 +0200    Sat, 27 Jun 2015 13:44:44 +0200    1    {kubelet kubernetes-minion-6fbi}    spec.containers{liveness}    started    Started with docker id ed6bb004ee10
```


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