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Community Blog Kubernetes : Configure Liveness and Readiness Probes

Kubernetes : Configure Liveness and Readiness Probes

This tutorial teaches you about the Liveness and Readiness probes to help ensure your Pods run smoothly.

By Alwyn Botha, Alibaba Cloud Tech Share Author. Tech Share is Alibaba Cloud's incentive program to encourage the sharing of technical knowledge and best practices within the cloud community.

This tutorial teaches you about two independent types of probes to help ensure your Pods run smoothly:

  • Liveness Probes: checks your containers are alive
  • Readiness Probes: checks your containers are able to do productive work

Kubernetes assumes responsibility that your containers in your Pods are alive. If not, it restarts the containers that fail liveness probes. Kubernetes do not assume responsibility for your Pods to be ready. Readiness may be a complicated set of interrelated networked components that enables a Pod to be ready.

Restarting a container with a failing readiness probe will not fix it, so readiness failures receive no automatic reaction from Kubernetes. A Pod may have several containers running inside it. All those containers may have different liveness and readiness probes ( since different software runs inside each ).

This tutorial demonstrates Pods with just one simple container. This way we can focus only on liveness and readiness probes.

This tutorial will cover the following topics:

  • httpGet livenessProbe: restartPolicy: Always
  • httpGet livenessProbe: restartPolicy: Never
  • httpGet livenessProbe: failureThreshold = 1
  • tcpSocket livenessProbe
  • tcpSocket readinessProbe
  • Readiness and liveness commands

1) httpGet livenessProbe: restartPolicy: Always

Create the following YAML file with your favorite Linux editor.

nano myLiveness-Pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: myliveness-pod
spec:
  containers:
  - image: httpd:2.4
    imagePullPolicy: IfNotPresent
    name: myliveness-container

    command: ['sh', '-c', 'echo Container 1 is Running ; sleep 3600']

    ports:
    - name: liveness-port
      containerPort: 80
      hostPort: 8080

    livenessProbe:
      httpGet:
        path: /
        port: 80
      initialDelaySeconds: 2
      periodSeconds: 10

Explanation of Pod spec above:

  • we use a httpd:2.4 image
  • image only gets downloaded from Docker hub once imagePullPolicy: IfNotPresent
  • command gives container work otherwise it just exits immediately upon startup
  • ports this container port containerPort: 80 will be accessible via hostPort: 8080
  • httpGet livenessProbe: access port 80 at path /
  • initialDelaySeconds: 2 waits 2 seconds after container got created before probing starts
  • periodSeconds: 10 liveness probe probes every 10 seconds.

A httpGet livenessProbe uses http get command to probe if a container is alive.

Let's create the Pod to see how this works.

Create the Pod.

kubectl create -f myLiveness-Pod.yaml

pod/myliveness-pod created

Truncated list of describe output ... only relevant fields shown.

kubectl describe pod/myliveness-pod

Name:               myliveness-pod
Status:             Running
Containers:
  myliveness-container:
    Image:         httpd:2.4
    Port:          80/TCP
    Host Port:     8080/TCP
    State:          Running
      Started:      Wed, 16 Jan 2019 07:37:02 +0200
    Ready:          True
    Restart Count:  0
    Liveness:       http-get http://:80/ delay=2s timeout=1s period=10s #success=1 #failure=3
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Scheduled  4s    default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal  Pulled     3s    kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal  Created    3s    kubelet, minikube  Created container
  Normal  Started    3s    kubelet, minikube  Started container

This Pod looks identical to any other successfully running Pod - zero difference even in events list. Liveness probes waiting those defined seconds before probing starts.

Still looks like any other Pod for first 30 seconds.

kubectl get po
NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   0          12s

kubectl get po
NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   0          22s

kubectl get po
NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   0          33s

Let's investigate what is happening in detail.

kubectl describe pod/myliveness-pod

Name:               myliveness-pod
Start Time:         Wed, 16 Jan 2019 07:37:01 +0200
Status:             Running
Containers:
  myliveness-container:
    State:          Running
      Started:      Wed, 16 Jan 2019 07:37:02 +0200
    Ready:          True
    Restart Count:  0
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Events:
  Type     Reason     Age               From               Message
  ----     ------     ----              ----               -------
  Normal   Scheduled  37s               default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     36s               kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    36s               kubelet, minikube  Created container
  Normal   Started    36s               kubelet, minikube  Started container
  Warning  Unhealthy  9s (x3 over 29s)  kubelet, minikube  Liveness probe failed: Get http://172.17.0.6:80/: dial tcp 172.17.0.6:80: connect: connection refused

We had 3 liveness probe failures so far. Overall Pod status stays READY and RUNNING. ( This is a confusing fact: the container is not alive, but it is in status: ready )

Wait around 15 seconds and redo describe


Events:
  Type     Reason     Age                From               Message
  ----     ------     ----               ----               -------
  Normal   Scheduled  62s                default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Warning  Unhealthy  34s (x3 over 54s)  kubelet, minikube  Liveness probe failed: Get http://172.17.0.6:80/: dial tcp 172.17.0.6:80: connect: connection refused
  Normal   Pulled     4s (x2 over 61s)   kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    4s (x2 over 61s)   kubelet, minikube  Created container
  Normal   Started    4s (x2 over 61s)   kubelet, minikube  Started container
  Normal   Killing    4s                 kubelet, minikube  Killing container with id docker://myliveness-container:Container failed liveness probe.. Container will be killed and recreated.
  • 62 seconds ago Pod got scheduled
  • 34 seconds ago liveness probe failed 3 times
  • 4 seconds ago: new container created

Apache is not running in the container. This causes liveness probe to fail. There is no working port 80 to connect to : dial tcp 172.17.0.6:80: connect: connection refused

Let's fix that. Enter the Pod and start apache:

kubectl exec myliveness-pod -i -t -- /bin/sh
# httpd
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 172.17.0.6. Set the 'ServerName' directive globally to suppress this message
# httpd
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 172.17.0.6. Set the 'ServerName' directive globally to suppress this message
httpd (pid 15) already running
# exit

AH00558 warning is easy to fix, but irrelevant to liveness probes, so feel free to ignore it.

I entered httpd twice - second time it shows it is running already ( exactly what I wanted to see ).

kubectl get po

NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   1          104s

Our Pod is running, it restarted once.

We fixed the problem.

Unhealthy 32s (x5 over 102s) will not shown any more failures.

8 seconds later

Warning Unhealthy 40s (x5 over 110s) kubelet, minikube Liveness probe failed: Get http://172.17.0.6:80/: dial tcp 172.17.0.6:80: connect: connection refused

20 seconds later

Warning Unhealthy 57s (x5 over 2m7s) kubelet, minikube Liveness probe failed: Get http://172.17.0.6:80/: dial tcp 172.17.0.6:80: connect: connection refused

Restart count does not increase anymore. Liveness probes succeed.

Unfortunately the events do not SHOW a log entry about this success. You have to deduce it and assume it now works. There is no field that displays the liveness status.

kubectl get po
NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   1          2m19s

kubectl get po
NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   1          2m27s

kubectl get po
NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   1          2m34s

kubectl get po
NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   1          2m45s

kubectl get po
NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   1          2m59s

Delete Pod.

kubectl delete -f myLiveness-Pod.yaml --force --grace-period=0

pod "myliveness-pod" force deleted

This demo worked since the default restartPolicy: Always is in effect.

2) httpGet livenessProbe: restartPolicy: Never

Let's see what happens with a restartPolicy: Never.

nano myLiveness-Pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: myliveness-pod
spec:
  containers:
  - image: httpd:2.4
    imagePullPolicy: IfNotPresent
    name: myliveness-container

    command: ['sh', '-c', 'echo Container 1 is Running ; sleep 3600']

    ports:
    - name: liveness-port
      containerPort: 80
      hostPort: 8080

    livenessProbe:
      httpGet:
        path: /
        port: 80
      initialDelaySeconds: 2
      periodSeconds: 2
      
  restartPolicy: Never

I made periodSeconds 2 seconds. Now we will quickly see what happens.

Create the Pod.

kubectl create -f myLiveness-Pod.yaml

pod/myliveness-pod created

Investigate just the tail ( events ) part of kubectl describe pod/myliveness-pod

Events:
  Type     Reason     Age              From               Message
  ----     ------     ----             ----               -------
  Normal   Scheduled  8s               default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     8s               kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    8s               kubelet, minikube  Created container
  Normal   Started    8s               kubelet, minikube  Started container
  Warning  Unhealthy  2s (x3 over 6s)  kubelet, minikube  Liveness probe failed: Get http://172.17.0.6:80/: dial tcp 172.17.0.6:80: connect: connection refused

6 seconds later ..........

Events:
  Type     Reason     Age               From               Message
  ----     ------     ----              ----               -------
  Normal   Scheduled  14s               default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     14s               kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    14s               kubelet, minikube  Created container
  Normal   Started    14s               kubelet, minikube  Started container
  Warning  Unhealthy  8s (x3 over 12s)  kubelet, minikube  Liveness probe failed: Get http://172.17.0.6:80/: dial tcp 172.17.0.6:80: connect: connection refused

10 seconds later .........

Events:
  Type     Reason     Age                From               Message
  ----     ------     ----               ----               -------
  Normal   Scheduled  25s                default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     25s                kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    25s                kubelet, minikube  Created container
  Normal   Started    25s                kubelet, minikube  Started container
  Warning  Unhealthy  19s (x3 over 23s)  kubelet, minikube  Liveness probe failed: Get http://172.17.0.6:80/: dial tcp 172.17.0.6:80: connect: connection refused

another 10 seconds later .........

Events:
  Type     Reason     Age                From               Message
  ----     ------     ----               ----               -------
  Normal   Scheduled  34s                default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     34s                kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    34s                kubelet, minikube  Created container
  Normal   Started    34s                kubelet, minikube  Started container
  Warning  Unhealthy  28s (x3 over 32s)  kubelet, minikube  Liveness probe failed: Get http://172.17.0.6:80/: dial tcp 172.17.0.6:80: connect: connection refused

restartPolicy: Never works. No restarts done.

The default failureThreshold is 3 times. After 3 failures a container is classified as failed.

Only 3 failed probes done.

Here we see the Pod status turns to error.

kubectl get po
NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   0          37s

kubectl get po
NAME             READY   STATUS   RESTARTS   AGE
myliveness-pod   0/1     Error    0          55s

kubectl get po
NAME             READY   STATUS   RESTARTS   AGE
myliveness-pod   0/1     Error    0          67s

Investigate overall Pod status (below) :

  • Pod Status: Failed
  • Container State: Terminated; Reason: Error; Exit Code: 137
  • Ready False; ContainersReady False
  • Restart Count: 0 ... because restartPolicy: Never

Pod status is failed: 3 liveness probe failures and restartPolicy: Never prevents Kubernetes from restarting it in an effort to fix it.

kubectl describe pod/myliveness-pod

Name:               myliveness-pod
Start Time:         Wed, 16 Jan 2019 07:45:47 +0200
Status:             Failed
Containers:
  myliveness-container:
    State:          Terminated
      Reason:       Error
      Exit Code:    137
      Started:      Wed, 16 Jan 2019 07:45:47 +0200
      Finished:     Wed, 16 Jan 2019 07:46:23 +0200
    Ready:          False
    Restart Count:  0
Conditions:
  Type              Status
  Initialized       True
  Ready             False
  ContainersReady   False
  PodScheduled      True

Delete Pod.

kubectl delete -f myLiveness-Pod.yaml --force --grace-period=0

pod "myliveness-pod" force deleted

3) httpGet livenessProbe: failureThreshold = 1

By default failureThreshold equals 3. 3 tries before container declared a failure.

Let's set failureThreshold equal to 1 and experiment. ( note last line in spec )

nano myLiveness-Pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: myliveness-pod
spec:
  containers:
  - image: httpd:2.4
    imagePullPolicy: IfNotPresent
    name: myliveness-container

    command: ['sh', '-c', 'echo Container 1 is Running ; sleep 3600']

    ports:
    - name: liveness-port
      containerPort: 80
      hostPort: 8080

    livenessProbe:
      httpGet:
        path: /
        port: 80
      initialDelaySeconds: 2
      periodSeconds: 2
      failureThreshold: 1      

Create the Pod.

kubectl create -f myLiveness-Pod.yaml

pod/myliveness-pod created

kubectl get po

NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   0          6s

After around a minute:

desc pod/myliveness-pod|tail

Events:
  Type     Reason     Age                From               Message
  ----     ------     ----               ----               -------
  Normal   Scheduled  64s                default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     31s (x2 over 64s)  kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    31s (x2 over 64s)  kubelet, minikube  Created container
  Normal   Started    31s (x2 over 64s)  kubelet, minikube  Started container
  Normal   Killing    31s                kubelet, minikube  Killing container with id docker://myliveness-container:Container failed liveness probe.. Container will be killed and recreated.
  Warning  Unhealthy  28s (x2 over 62s)  kubelet, minikube  Liveness probe failed: Get http://172.17.0.6:80/: dial tcp 172.17.0.6:80: connect: connection refused

Determine number of restarts:

kubectl get po

NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   2          68s

2 restarts after 2 liveness probe failures.

Another 30 seconds later.

desc pod/myliveness-pod|tail

Events:
  Type     Reason     Age                From               Message
  ----     ------     ----               ----               -------
  Normal   Scheduled  86s                default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     20s (x3 over 86s)  kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    20s (x3 over 86s)  kubelet, minikube  Created container
  Normal   Started    20s (x3 over 86s)  kubelet, minikube  Started container
  Normal   Killing    20s (x2 over 53s)  kubelet, minikube  Killing container with id docker://myliveness-container:Container failed liveness probe.. Container will be killed and recreated.
  Warning  Unhealthy  18s (x3 over 84s)  kubelet, minikube  Liveness probe failed: Get http://172.17.0.6:80/: dial tcp 172.17.0.6:80: connect: connection refused

Determine number of restarts:

kubectl get po

NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   1/1     Running   3          108s

3 restarts after 3 liveness probe failures.

You have to determine the suitable failureThreshold for your production environment.

Different containers in the same Pod may have / need different suitable failureThreshold values.

The default timeoutSeconds is one seconds.

Similary, you have to determine the suitable timeoutSeconds for your production environment - for each container with different software.

Delete Pod.

kubectl delete -f myLiveness-Pod.yaml --force --grace-period=0

pod "myliveness-pod" force deleted

4) tcpSocket livenessProbe

Till now we used httpGet livenessProbes

For software that does not support http gets, you can use tcp Socket liveness probes.

Create using your editor:

nano myLiveness-Pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: myliveness-pod
spec:
  containers:
  - image: httpd:2.4
    imagePullPolicy: IfNotPresent
    name: myliveness-container

    command: ['sh', '-c', 'echo Container 1 is Running ; sleep 3600']

    ports:
    - name: liveness-port
      containerPort: 80
      hostPort: 8080

    livenessProbe:
      tcpSocket:
        port: 80
      initialDelaySeconds: 3
      periodSeconds: 10

Only difference from before is tcpSocket instead of httpGet

Create the Pod.

kubectl create -f myLiveness-Pod.yaml

pod/myliveness-pod created

Based on what you learned so far you can do this exercise on your own.

Container liveness probes will fail.

The following will fix it, just as before.

kubectl exec myliveness-pod -i -t -- /bin/sh
# httpd
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 172.17.0.6. Set the 'ServerName' directive globally to suppress this message
# exit

Delete Pod.

kubectl delete -f myLiveness-Pod.yaml --force --grace-period=0

pod "myliveness-pod" force deleted

Based on the software running in each of your production containers you have to determine which liveness probe to use:

  • tcpSocket
  • httpGet

5) tcpSocket readinessProbe

We did liveness probes thus far.

Readinessprobes are independent of liveness probes.

Readinessprobes probe to ensure your containers are ready to do productive work.

You have to determine exactly what to test to ensure a readiness probe tests readiness.

readinessProbe and livenessProbe syntax are identical.

You can have both these probes defined for a Pod.

Our Pod spec below demonstrates one readiness probe.

nano myLiveness-Pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: myliveness-pod
spec:
  containers:
  - image: httpd:2.4
    imagePullPolicy: IfNotPresent
    name: myliveness-container

    command: ['sh', '-c', 'echo Container 1 is Running ; sleep 3600']

    ports:
    - name: liveness-port
      containerPort: 80
      hostPort: 8080
    
    readinessProbe:
      tcpSocket:
        port: 80
      initialDelaySeconds: 3
      periodSeconds: 2

Note we use short delay seconds at bottom of spec: to see what happens quickly.

Create the Pod.

kubectl create -f myLiveness-Pod.yaml

pod/myliveness-pod created

The Pod is running on the node, but it is not ready. Kubernetes noticed the readiness probe that needs to succeed. Then it will convert the ready state to true.

kubectl get po

NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   0/1     Running   0          3s

Truncated list of describe output ... only relevant EVENT fields shown.

Events:
  Type     Reason     Age              From               Message
  ----     ------     ----             ----               -------
  Normal   Scheduled  9s               default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     8s               kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    8s               kubelet, minikube  Created container
  Normal   Started    8s               kubelet, minikube  Started container
  Warning  Unhealthy  1s (x3 over 5s)  kubelet, minikube  Readiness probe failed: dial tcp 172.17.0.6:80: connect: connection refused

Last line: readiness probe failed 3 times.

6 seconds later ...

Events:
  Type     Reason     Age               From               Message
  ----     ------     ----              ----               -------
  Normal   Scheduled  21s               default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     20s               kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    20s               kubelet, minikube  Created container
  Normal   Started    20s               kubelet, minikube  Started container
  Warning  Unhealthy  1s (x9 over 17s)  kubelet, minikube  Readiness probe failed: dial tcp 172.17.0.6:80: connect: connection refused

6 more failures.

Another 10 seconds later ...

Events:
  Type     Reason     Age                From               Message
  ----     ------     ----               ----               -------
  Normal   Scheduled  31s                default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     30s                kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    30s                kubelet, minikube  Created container
  Normal   Started    30s                kubelet, minikube  Started container
  Warning  Unhealthy  1s (x14 over 27s)  kubelet, minikube  Readiness probe failed: dial tcp 172.17.0.6:80: connect: connection refused

Another 5 failures. Note no mention of restarts. Kubernetes does not restart failed readiness probes.

This is the MAJOR difference between readiness and liveness probes.

kubectl get po

NAME             READY   STATUS    RESTARTS   AGE
myliveness-pod   0/1     Running   0          36s

Detailed Pod status:

  • Pod: Ready False
  • Containers: ContainersReady False
kubectl describe pod/myliveness-pod

Name:               myliveness-pod
Status:             Running
Containers:
  myliveness-container:
    State:          Running
      Started:      Wed, 16 Jan 2019 08:42:09 +0200
    Ready:          False
    Restart Count:  0
Conditions:
  Type              Status
  Initialized       True
  Ready             False
  ContainersReady   False
  PodScheduled      True

Events:
  Type     Reason     Age                 From               Message
  ----     ------     ----                ----               -------
  Normal   Scheduled  73s                 default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     72s                 kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    72s                 kubelet, minikube  Created container
  Normal   Started    72s                 kubelet, minikube  Started container
  Warning  Unhealthy  27s (x22 over 69s)  kubelet, minikube  Readiness probe failed: dial tcp 172.17.0.6:80: connect: connection refused

Fix the Pod, start Apache.

kubectl exec myliveness-pod -i -t -- /bin/sh
# httpd
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 172.17.0.6. Set the 'ServerName' directive globally to suppress this message
# exit

Check Pod status again ... now it is ready

kubectl describe pod/myliveness-pod

Name:               myliveness-pod
Status:             Running
Containers:
  myliveness-container:
    State:          Running
      Started:      Wed, 16 Jan 2019 08:42:09 +0200
    Ready:          True
    Restart Count:  0
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True

Events:
  Type     Reason     Age                 From               Message
  ----     ------     ----                ----               -------
  Normal   Scheduled  99s                 default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     98s                 kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    98s                 kubelet, minikube  Created container
  Normal   Started    98s                 kubelet, minikube  Started container
  Warning  Unhealthy  53s (x22 over 95s)  kubelet, minikube  Readiness probe failed: dial tcp 172.17.0.6:80: connect: connection refused

A minute later. x22 failed readiness probe count does not increase anymore.

Events:
  Type     Reason     Age                   From               Message
  ----     ------     ----                  ----               -------
  Normal   Scheduled  2m19s                 default-scheduler  Successfully assigned default/myliveness-pod to minikube
  Normal   Pulled     2m18s                 kubelet, minikube  Container image "httpd:2.4" already present on machine
  Normal   Created    2m18s                 kubelet, minikube  Created container
  Normal   Started    2m18s                 kubelet, minikube  Started container
  Warning  Unhealthy  93s (x22 over 2m15s)  kubelet, minikube  Readiness probe failed: dial tcp 172.17.0.6:80: connect: connection refused

Delete Pod.

kubectl delete -f myLiveness-Pod.yaml --force --grace-period=0

pod "myliveness-pod" force deleted

This final exercise demonstrated THE readiness versus liveness difference:

  • Liveness failures - Kubernetes restarts the failed container
  • Readiness failures - Kubernetes does nothing when a container fails. ContainersReady set to False

Excellent official reference documentation about liveness and readyness probe settings:

https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-probes/#configure-probes

Conclusion: Readiness and Liveness Commands

We only did tcp socket and http get probes in this tutorial. The last way to do probes is via commands.

Official Kubernetes demo using commands

https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-probes/#define-a-liveness-command

As a final exercise I suggest you follow those instructions.

You will note that the kubectl describe pod/myliveness-pod output they show is using a previous format.

This concludes this tutorial.

Carefully read the text of that last link and determine appropriate settings for each container in each Pod in your production environment.

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