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application runtime Ephemeral container and Pod

An abcdesktop application can run as a kubernetes ephemeral container or as a pod.

An ephemeral container can access to share memory shm with the X11 server. An ephemeral container run always on the same node as the user pod, where the graphical container 'X11 server' is running. An ephemeral container does not prevent cpu and memory resource limits.

A pod can't access to share memory with the X11 server. An kubernetes pod can run on separated node from the user's pod node. For a pod, you can specify resource limits.

ephemeralcontainerversuspod

To describe the difference between ephemeral-container and pod-application, we use the game 2048, one instance come from alpine based on gtk, the second one come from ubuntu based on qt

  • 2048-alpine is a GTK application, and is defined to run as ephemeral-container
  • 2048-ubuntu is a QT application, and is defined to run as a kubernetes pod

Requirements

  • jq command preinstalled.

Start a shell to your abcdesktop server

Get a shell to your abcdestkop server.

Download 2048-alpine and 2048-ubuntu json files

Open a shell to your abcdesktop server

curl --output 2048-alpine.d.3.0.json https://raw.githubusercontent.com/abcdesktopio/oc.apps/main/2048-alpine.d.3.0.json
curl --output 2048-ubuntu.d.3.0.json https://raw.githubusercontent.com/abcdesktopio/oc.apps/main/2048-ubuntu.d.3.0.json

Check that the json files are downloaded

$ ls -la *.json
-rw-r--r-- 1 root root 29183 Dec 28 16:24 2048-alpine.d.3.0.json
-rw-r--r-- 1 root root 29099 Dec 28 16:24 2048-ubuntu.d.3.0.json

Look at the label oc.containerengine for each json file

Read the label oc.containerengine for 2048-alpine

cat 2048-alpine.d.3.0.json | jq -r '.[0].Config.Labels."oc.containerengine"'

The response is ephemeral_container

ephemeral_container

This application 2048-alpine will start as an ephemeral_container

Read the label oc.containerengine for 2048-alpine

cat 2048-ubuntu.d.3.0.json | jq -r '.[0].Config.Labels."oc.containerengine"'

The response is pod_application

pod_application

This application 2048-ubuntu will start as a pod_application, it's a pod.

PUT 2048-alpine and 2048-ubuntu applications to your abcdesktop service

curl -X PUT -H 'Content-Type: text/javascript' http://localhost:30443/API/manager/image -d @2048-alpine.d.3.0.json
curl -X PUT -H 'Content-Type: text/javascript' http://localhost:30443/API/manager/image -d @2048-ubuntu.d.3.0.json

Each curl command returns a complete json document.

Wait for the pull pod are Ready

kubectl wait --for=condition=Ready pods --selector=type=pod_application --timeout=-1s -n abcdesktop

Wait for condition met

pod/pull-2048-alpine-install-4280c633e777dceb3f529f208b442c0dff891 condition met
pod/pull-2048-ubuntu-install-ee652f4ff381655768bcc09d54a9b62ab7684 condition met

Login to your abcdesktop service

Using a web browser, open the abcdesktop service url. If your are running abcdesktop on your local device, the url should be : 

http://localhost:30443

Choose to login as hermes

Login in as the user Hermes Conrad

  • Login: Hermes Conrad
  • Password: hermes

Look for 2048

Your desktop is created

Your desktop is created. By default your dock is empty.

Look for 2048

Look for 2048

In the search text area, write the keyword 2048

Look for 2048

The two applications appear in the search result applications area.

Start each 2048 application

Start 2048-ubuntu and 2048-alpine application

Look for 2048

2048-ubuntu and 2048-alpine applications start. The application 2048-alpine can start quickly than the application 2048-ubuntu.

  • 2048-alpine is an ephemeral container attached to the graphical container.
  • 2048-ubuntu is a complete kubernetes pod.

Let's have a look on your server side

Get pod application

Get the running pod using kubectl get pods -n abcdesktop

kubectl get pods -n abcdesktop
NAME                            READY   STATUS    RESTARTS   AGE
hermes-app-2048-ubuntu-4dd6f    1/1     Running   0          8s
hermes-db906                    4/4     Running   0          100s
memcached-od-57c57c4f9d-92fs2   1/1     Running   0          38m
mongodb-od-f69ff6b5b-v6ztc      1/1     Running   0          38m
nginx-od-58f86c4dc8-8n9lf       1/1     Running   0          25m
openldap-od-d66d66bf4-84lg8     1/1     Running   0          38m
pyos-od-5586b88767-gsdl8        1/1     Running   0          14m
speedtest-od-6c59bdff75-n6s66   1/1     Running   0          38m

The application 2048-ubuntu is listed as a pod. The application 2048-ubuntu is a pod. The prefix is the $userid-app for example hermes-app-2048-ubuntu-4dd6f, followed by the application name 2048-ubuntu and a uuid.

The application 2048-alpine is not a pod.

The application 2048-alpine is listed as an ephemeral container, inside the user pod hermes-db906

kubectl get pods hermes-db906  -o json -n abcdesktop | jq -r ".status.ephemeralContainerStatuses"

The application 2048-alpine.d is listed in the .status.ephemeralContainerStatuses 

[
  {
    "containerID": "containerd://eb5c1c4c19e5581dfd6a7290f46b63ce073b318bc1f9980bd3e37153cb66e44b",
    "image": "docker.io/abcdesktopio/2048-alpine.d:3.0",
    "imageID": "docker.io/abcdesktopio/2048-alpine.d@sha256:2c3c46c22689b8f91cbd5ebd4d5f80c95bc5ba9b1e23f13aebb54121d2f6d590",
    "lastState": {},
    "name": "hermes-conrad-2048-alpine-1eef4",
    "ready": false,
    "restartCount": 0,
    "state": {
      "terminated": {
        "containerID": "containerd://eb5c1c4c19e5581dfd6a7290f46b63ce073b318bc1f9980bd3e37153cb66e44b",
        "exitCode": 0,
        "finishedAt": "2023-05-17T14:38:13Z",
        "reason": "Completed",
        "startedAt": "2023-05-17T14:37:00Z"
      }
    }
  }
]

Ephemeral container versus Pod application

An ephemeral container can access to share memory shm with the X11 server. An ephemeral container run always on the same node as the X11 server.

A pod can't access to share memory with the X11 server. An Kubernetes pod can run on a separated node from the X11 server.

If your application need to share memory with X11 server, when you have to set the oc.containerengine label to ephemeral_container.

Compare kubernetes ephemeral container and pod

Kubernetes ephemeral container

Use an ephemeral container to start an application have some advantages and some disadvantages.

advantages

  • Start quickly
  • Less system resources than a pod
  • Share Process Namespace is allowed shareProcessNamespace: true
  • Share memory shm is allowed
  • Share the network stack (IP Address) of the user pod

disadvantages

  • resources is disallowed
  • no limits and requests (cpu, memory)
  • nodeSelector not supported

Kubernetes Pod

Use a kubernetes pod to start an application have some advantages and some disadvantages.

advantages

  • resources (cpu, memory) is allowed
  • limits and requests are supported
  • ports, livenessProbe, readinessProbe are allowed
  • nodeSelector support an application can run on a dedicated node (for example with GPU)
  • can use a dedicated network to route application data

disadvantages

  • More system resources than an ephemeral container
  • Need X11 tcp port enabled on the user pod 'X11LISTEN': 'tcp'
  • Increase network resource if application pod and user pod run a distinct host

Troubleshooting

Troubleshooting BadShmSeg error

If you configure 2048-alpine with gtk to start as a pod and not as an ephemeral container, you will get the BadShmSeg error

Install the application 2048-alpine-with-error

curl --output 2048-alpine.d.3.0.json https://raw.githubusercontent.com/abcdesktopio/oc.apps/main/2048-alpine-with-error.d.3.0.json
2048-alpine-with-error.d.3.0.json

PUT 2048-alpine-with-error applications to your abcdesktop service

curl -X PUT -H 'Content-Type: text/javascript' http://localhost:30443/API/manager/image -d @2048-alpine-with-error.d.3.0.json

Wait for the pulled pod are Ready

kubectl wait --for=condition=Ready pods --selector=type=pod_application_pull --timeout=-1s -n abcdesktop

Wait for condition met

pod/pull-2048-alpine-with-error-install-935509a58088531ae57756 condition met

Login to your abcdesktop service

Using a web browser, open the abcdesktop service url. If your are running abcdesktop on your local device, the url should be : 

http://localhost:30443

Choose to login as hermes

Login in as the user Hermes Conrad

  • Login: Hermes Conrad
  • Password: hermes

Look for 2048

Your desktop is created

Your desktop is created. By default your dock is empty.

Look for 2048

Look for 2048

In the search text area, write the keyword 2048

Look for 2048

The three applications appear in the search result applications area.

Start the 2048 (alpine gtk with error) application. It uses shared segment with X Window System, it must run as an ephemeral container, but as a pod it fails. The application starts but exit after few seconds, the content of the application does not appear.

alpine gtk with error

In the abcdesktop menu, choose Settings | Tasks.

alpine gtk with error

Then select the Logs button. The error was 'BadShmSeg (invalid shared segment parameter)'.

(org.gnome.TwentyFortyEight:36): Gdk-WARNING **: 10:14:26.185: The program 'org.gnome.TwentyFortyEight' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadShmSeg (invalid shared segment parameter)'.
(Details: serial 820 error_code 128 request_code 131 (MIT-SHM) minor_code 3)
(Note to programmers: normally, X errors are reported asynchronously;
that is, you will receive the error a while after causing it.
To debug your program, run it with the GDK_SYNCHRONIZE environment
variable to change this behavior. You can then get a meaningful
backtrace from your debugger if you break on the gdk_x_error() function.)

If you are running QT application, you can disable the X11 MIT Shared Memory Extension support. The MIT-SHM is an extension to the X server which allows faster transactions by using shared memory. Container isolation blocks it. Qt applications can be forced not to use the extension, by setting the variable QT_X11_NO_MITSHM value to 1.

QT_X11_NO_MITSHM=1

Note your can also use QT_XCB_NO_MITSHM value to 1

Troubleshooting chromium application

For chromium application disabled shm-usage with the parameters --disable-dev-shm-usage

Troubleshooting cannot open display or could not connect to display error

When you start an application the log file write cannot open display error

kubectl logs hermes-app-2048-ubuntu-c7360cd025d04813ad5e0af74b6df4ba  -n abcdesktop 

qt.qpa.xcb: could not connect to display 172.17.0.10:0
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.

Using the web shell inside an abcdesktop session, start netstat -a command line

The result should show that the process Xvnc is listening on tcp port number 6000

netstat-listentcp

hermes:~$ netstat  -anp
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:6000            0.0.0.0:*               LISTEN      82/Xvnc

If Xvnc is not listening on tcp port number 6000

netstat-nolistentcp

Update od.config to make Xvnc listen on tcp port number 6000

Open your od.config file, and look at the desktop.envlocal option.

Add 'X11LISTEN': 'tcp' to the dictionary :

desktop.envlocal :  {   'DISPLAY'               : ':0.0',
                        'SET_DEFAULT_WALLPAPER' : 'welcometoabcdesktop.png',
                        'X11LISTEN'             : 'tcp' }

Save your local od.config file.

To apply changes, you can replace the abcdesktop-config

kubectl delete configmap abcdesktop-config -n abcdesktop
kubectl create configmap abcdesktop-config --from-file=od.config -n abcdesktop

Then restart pyos pod

kubectl delete pod -l run=pyos-od -n abcdesktop

You should read on stdout

pod "pyos-od-5586b88767-mrf28" deleted