Tutorials:Run the example container on the cluster

Requirements

• A working connection and login to the Kubernetes cluster.
• A valid namespace selected with authorization to run pods.
• A test container pushed to the CCU docker registry.

Set up a Kubernetes job script

Download the Kubernetes samples and look at job script in example_1. Alternatively, create your own directory and file named "job_script.yaml". Edit the contents as follows and replace all placeholders with your data:

apiVersion: batch/v1
kind: Job
metadata:
  # name of the job
  name: tf-mnist

spec:
  template:
    spec:
      # List of containers belonging to the job starts here
      containers:
      # container name used for pod creation
      - name: tf-mnist-container
        # container image from the registry
        image: ccu.uni-konstanz.de:5000/bastian.goldluecke/tf_mnist:0.1

        # container resources requested from the node
        resources:
          # requests are minimum resourcerequirements
          requests:
            # this gives us a minimum 2 GiB of main memory to work with.
            memory: "2Gi"

          # limits are maximum resource allocations
          limits:
            # this gives an absolute limit of 3 GiB of main memory.
            # exceeding it will mean the container exits immediately with an error.
            memory: "3Gi"

            # this requests a number of GPUs. GPUs will be allocated to the container
            # exclusively. No fractional GPUs can be requested.
            # When executing nvidia-smi in the container, it should show exactly this
            # number of GPUs.
            #
            # PLEASE DO NOT SET THE NUMBER TO ZERO, EVER, AND ALWAYS INCLUDE THIS LINE.
            # ALWAYS PUT IT IN THE SECTION "limits", NOT "requests".
            #
            # It is a known limitation of nVidias runtime that if zero GPUs are requested,
            # then actually *all* GPUs are exposed in the container.
            # We are looking for a fix to this.
            #
            nvidia.com/gpu: "1"

        # the command which is executed after container creation
        command: ["/application/run.sh"]


      # login credentials to the docker registry.
      # for convenience, a readonly credential is provided as a secret in each namespace.
      imagePullSecrets:
      - name: registry-ro-login

      # containers will never restart
      restartPolicy: Never

  # number of retries after failure.
  # since we typically have to fix something in this case, set to zero by default.
  backoffLimit: 0

When we start this job, it will create a single container based on the image we previously uploaded to the registry on a suitable node which serves the selected namespace of the cluster.

> kubectl apply -f job_script.yaml

Checking in on the job

We first check if our container is running.

> kubectl get pods
# somewhere in the output you should see a line like this:
NAME             READY   STATUS    RESTARTS   AGE
tf-mnist-xxxx   1/1     Running   0          7s

Now that you now the name of the pod, you can check in on the logs:

# replace xxxx with the code from get pods.
> kubectl logs tf-mnist-xxxx
# this should show the console output of your python program

or get some more information about the job, the node the pod was placed on etc.

> kubectl describe job tf-mnist
# replace xxxx with the code from get pods.
> kubectl describe pod tf-mnist-xxxx

You can also open a shell in the running container, just as with docker:

> kubectl exec -it tf-mnist-xxxx /bin/bash
root@tf-mnist-xxxxx:/workspace# nvidia-smi
Tue Jun 18 14:25:00 2019       
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 418.67       Driver Version: 418.67       CUDA Version: 10.1     |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|===============================+======================+======================|
|   0  Tesla V100-SXM3...  On   | 00000000:E7:00.0 Off |                    0 |
| N/A   39C    P0    68W / 350W |  30924MiB / 32480MiB |      6%      Default |
+-------------------------------+----------------------+----------------------+
                                                                               
+-----------------------------------------------------------------------------+
| Processes:                                                       GPU Memory |
|  GPU       PID   Type   Process name                             Usage      |
|=============================================================================|
+-----------------------------------------------------------------------------+
root@tf-mnist-xxxxx:/workspace# ls /application/
nn.py  run.sh  tf-mnist.py
root@tf-mnist-xxxxx:/workspace#

Shutting down the job early

If while inspecting the job you notice that it does not run correctly, you can shut it down prematurely with

> kubectl delete -f job_script.yaml

Note that this also deletes all data your container might have written to its filesystem layer. If you want to save your trained models, you have to mount persistent volumes from the Kubernetes cluster into the container. This is covered in the persistent volume tutorial.