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

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<h1>*** PLEASE NOTE: This document applies to the HEAD of the source
tree only. If you are using a released version of Kubernetes, you almost
certainly want the docs that go with that version.</h1>

<strong>Documentation for specific 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: HTTP checks and container execution checks.

The [exec-liveness.yaml](exec-liveness.yaml) demonstrates the container execution check.
```
    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,
```
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.
```
    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:
```
# kubectl create -f exec-liveness.yaml
# kubectl create -f http-liveness.yaml
```

Check the status of the pods once they are created:
```
# 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:
```
# 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.

```
# 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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