MXNet Training (MXJob)

Using MXJob to train a model with Apache MXNet

This guide walks you through using Apache MXNet (incubating) with Kubeflow.

MXNet Operator provides a Kubernetes custom resource MXJob that makes it easy to run distributed or non-distributed Apache MXNet jobs (training and tuning) and other extended framework like BytePS jobs on Kubernetes. Using a Custom Resource Definition (CRD) gives users the ability to create and manage Apache MXNet jobs just like built-in K8S resources.

The Kubeflow implementation of MXJob is in training-operator.

Installing MXNet Operator

If you haven’t already done so please follow the Getting Started Guide to deploy Kubeflow.

By default, MXNet Operator will be deployed as a controller in training operator.

If you want to install a standalone version of the training operator without Kubeflow, see the kubeflow/training-operator’s README.

Verify that MXJob support is included in your Kubeflow deployment

Check that the Apache MXNet custom resource is installed:

kubectl get crd

The output should include like the following:

NAME                                             CREATED AT
...                              2021-09-06T18:33:57Z

Check that the Training operator is running via:

kubectl get pods -n kubeflow

The output should include training-operator-xxx like the following:

NAME                                READY   STATUS    RESTARTS   AGE
training-operator-d466b46bc-xbqvs   1/1     Running   0          4m37s

Creating a Apache MXNet training job

You create a training job by defining a MXJob with MXTrain mode and then creating it with.

kubectl create -f

Each mxReplicaSpecs defines a set of Apache MXNet processes. The mxReplicaType defines the semantics for the set of processes. The semantics are as follows:


  • A job must have 1 and only 1 scheduler
  • The pod must contain a container named mxnet
  • The overall status of the MXJob is determined by the exit code of the mxnet container
    • 0 = success
    • 1 || 2 || 126 || 127 || 128 || 139 = permanent errors:
      • 1: general errors
      • 2: misuse of shell builtins
      • 126: command invoked cannot execute
      • 127: command not found
      • 128: invalid argument to exit
      • 139: container terminated by SIGSEGV(Invalid memory reference)
    • 130 || 137 || 143 = retryable error for unexpected system signals:
      • 130: container terminated by Control-C
      • 137: container received a SIGKILL
      • 143: container received a SIGTERM
    • 138 = reserved in training-operator for user specified retryable errors
    • others = undefined and no guarantee


  • A job can have 0 to N workers
  • The pod must contain a container named mxnet
  • Workers are automatically restarted if they exit


  • A job can have 0 to N servers
  • parameter servers are automatically restarted if they exit

For each replica you define a template which is a K8S PodTemplateSpec. The template allows you to specify the containers, volumes, etc… that should be created for each replica.

Creating a TVM tuning job (AutoTVM)

TVM is a end to end deep learning compiler stack, you can easily run AutoTVM with MXJob. You can create a auto tuning job by define a type of MXTune job and then creating it with

kubectl create -f

Before you use the auto-tuning example, there is some preparatory work need to be finished in advance. To let TVM tune your network, you should create a docker image which has TVM module. Then, you need a auto-tuning script to specify which network will be tuned and set the auto-tuning parameters. For more details, please see tutorials. Finally, you need a startup script to start the auto-tuning program. In fact, MXJob will set all the parameters as environment variables and the startup script needs to read these variable and then transmit them to the auto-tuning script.

Using GPUs

MXNet Operator supports training with GPUs.

Please verify your image is available for distributed training with GPUs.

For example, if you have the following, MXNet Operator will arrange the pod to nodes to satisfy the GPU limit.

command: ["python"]
args: ["/incubator-mxnet/example/image-classification/","--num-epochs","1","--num-layers","2","--kv-store","dist_device_sync","--gpus","0"]
  limits: 1

Monitoring your Apache MXNet job

To get the status of your job

kubectl get -o yaml mxjobs $JOB

Here is sample output for an example job

kind: MXJob
  creationTimestamp: 2021-03-24T15:37:27Z
  generation: 1
  name: mxnet-job
  namespace: default
  resourceVersion: "5123435"
  selfLink: /apis/
  uid: xx11013b-4a28-11e9-s5a1-704d7bb912f91
    cleanPodPolicy: All
  jobMode: MXTrain
      replicas: 1
      restartPolicy: Never
          creationTimestamp: null
            - image: mxjob/mxnet:gpu
              name: mxnet
                - containerPort: 9091
                  name: mxjob-port
              resources: {}
      replicas: 1
      restartPolicy: Never
          creationTimestamp: null
            - image: mxjob/mxnet:gpu
              name: mxnet
                - containerPort: 9091
                  name: mxjob-port
              resources: {}
      replicas: 1
      restartPolicy: Never
          creationTimestamp: null
            - args:
                - /incubator-mxnet/example/image-classification/
                - --num-epochs
                - "10"
                - --num-layers
                - "2"
                - --kv-store
                - dist_device_sync
                - --gpus
                - "0"
                - python
              image: mxjob/mxnet:gpu
              name: mxnet
                - containerPort: 9091
                  name: mxjob-port
  completionTime: 2021-03-24T09:25:11Z
    - lastTransitionTime: 2021-03-24T15:37:27Z
      lastUpdateTime: 2021-03-24T15:37:27Z
      message: MXJob mxnet-job is created.
      reason: MXJobCreated
      status: "True"
      type: Created
    - lastTransitionTime: 2021-03-24T15:37:27Z
      lastUpdateTime: 2021-03-24T15:37:29Z
      message: MXJob mxnet-job is running.
      reason: MXJobRunning
      status: "False"
      type: Running
    - lastTransitionTime: 2021-03-24T15:37:27Z
      lastUpdateTime: 2021-03-24T09:25:11Z
      message: MXJob mxnet-job is successfully completed.
      reason: MXJobSucceeded
      status: "True"
      type: Succeeded
    Scheduler: {}
    Server: {}
    Worker: {}
  startTime: 2021-03-24T15:37:29Z

The first thing to note is the RuntimeId. This is a random unique string which is used to give names to all the K8s resouces (e.g Job controllers & services) that are created by the MXJob.

As with other K8S resources status provides information about the state of the resource.

phase - Indicates the phase of a job and will be one of

  • Creating
  • Running
  • CleanUp
  • Failed
  • Done

state - Provides the overall status of the job and will be one of

  • Running
  • Succeeded
  • Failed

For each replica type in the job, there will be a ReplicaStatus that provides the number of replicas of that type in each state.

For each replica type, the job creates a set of K8s Job Controllers named


For example, if you have 2 servers and the runtime id is “76n0”, then MXJob will create the following two jobs:


More Information


Was this page helpful?