How to Use Advanced Job Settings

Parameters and Secrets

It is common to train models with different parameters. OpenPAI supports parameter definition and reference, which provides a flexible way of training and comparing models. You can define your parameters in the Parameters section and reference them by using <% $parameters.paramKey %> in your commands. For example, the following picture shows how to define the Quick Start job using a stepNum parameter.

You can define batch size, learning rate, or whatever you want as parameters to accelerate your job submission.

In some cases, it is desired to define some secret messages such as passwords, tokens, etc. You can use the Secrets section for the definition. The usage is the same as parameters except that secrets will not be displayed or recorded.

Multiple Task Roles

If you use the Distributed button to submit jobs, then you can add different task roles for your job.

What is a task role? For single server jobs, there is only one task role. For distributed jobs, there may be multiple task roles. For example, when TensorFlow is used to run distributed jobs, it has two roles, including the parameter server and the worker.

Instances in the following picture is the number of instances of certain task roles. In distributed jobs, it depends on how many instances are needed for a task role. For example, if you set instances to 8 for a TensorFlow worker task role, it means there should be 8 Docker containers for the worker role.

Environmental Variables and Port Reservation

In a distributed job, one task might communicate with others (When we say task, we mean a single instance of a task role). So a task needs to be aware of other tasks' runtime information such as IP, port, etc. The system exposes such runtime information as environment variables to each task's Docker container. For mutual communication, users can write code in the container to access those runtime environment variables.

Below we show a complete list of environment variables accessible in a Docker container:

Category Environment Variable Name Description
Job level PAI_JOB_NAME jobName in config file
PAI_USER_NAME User who submit the job
PAI_DEFAULT_FS_URI Default file system uri in PAI
Task role level PAI_TASK_ROLE_COUNT Total task roles' number in config file
PAI_TASK_ROLE_LIST Comma separated all task role names in config file
PAI_TASK_ROLE_TASK_COUNT_$taskRole Task count of the task role
PAI_HOST_IP_$taskRole_$taskIndex The host IP for taskIndex task in taskRole
PAI_PORT_LIST_$taskRole_$taskIndex_$portType The $portType port list for taskIndex task in taskRole
PAI_RESOURCE_$taskRole Resource requirement for the task role in "gpuNumber,cpuNumber,memMB,shmMB" format
PAI_MIN_FAILED_TASK_COUNT_$taskRole taskRole.minFailedTaskCount of the task role
PAI_MIN_SUCCEEDED_TASK_COUNT_$taskRole taskRole.minSucceededTaskCount of the task role
Current task role PAI_CURRENT_TASK_ROLE_NAME of current task role
Current task PAI_CURRENT_TASK_ROLE_CURRENT_TASK_INDEX Index of current task in current task role, starting from 0

Some environmental variables are in association with ports. In OpenPAI, you can reserve ports for each task in advanced settings, as shown in the image below:

The ports you reserved are available in environmental variables like PAI_PORT_LIST_$taskRole_$taskIndex_$portLabel, where $taskIndex means the instance index of that task role.

For a detailed summary, there are two ways to reference a declared port (list):



  • use a to-be-deprecated environmental variable to get port (list) in current container like

Job Exit Spec, Retry Policy, and Completion Policy

There are always different kinds of errors in jobs. In OpenPAI, errors are classified into 3 categories automatically:

  1. Transient Error: This kind of error is considered transient. There is a high chance to bypass it through a retry.
  2. Permanent Error: This kind of error is considered permanent. Retries may not help.
  3. Unknown Error: Errors besides transient error and permanent error.

In jobs, transient errors will be always retried, and permanent errors will never be retried. If an unknown error happens, PAI will retry the job according to user settings. To set a retry policy and completion policy for your job, please toggle the Advanced mode, as shown in the following image:

Here we have 3 settings: Retry count, Task retry count, and Completion policy. To explain them, we should be aware that a job is made up of multiple tasks. One task stands for a single instance in a task role. Task retry count is used for task-level retry. Retry count and Completion policy are used for job-level retry.

Firstly, let's look at Retry count and Completion policy.

In Completion policy, there are settings for Min Failed Instances and Min Succeed Instances. Min Failed Instances means the number of failed tasks to fail the entire job. It should be -1 or no less than 1. If it is set to -1, the job will always succeed regardless of any task failure. The default value is 1, which means 1 failed task will cause an entire job failure. Min Succeed Instances means the number of succeeded tasks to succeed the entire job. It should be -1 or no less than 1. If it is set to -1, the job will only succeed until all tasks are completed and Min Failed Instances is not triggered. The default value is -1.

If a job: 1. doesn't succeed after it satisfies Completion policy, 2. fails with an unknown error, and 3. has a Retry count larger than 0, the whole job will be retried. Set Retry count to a larger number if you need more retries.

Finally, for Task retry count, it is the maximum retry number for a single task. A special notice is that this setting won't work unless you set extras.gangAllocation to false in the job protocol.

Job Protocol, Export and Import Jobs

In OpenPAI, all jobs are represented by YAML, a markup language. You can click the button Edit YAML to edit the YAML definition directly:

Use the Save button to apply any changes:

You can also export and import YAML files using the Export and Import buttons.

To see a full reference of job protocol, please check job protocol.

Use Prerequisites

OpenPAI protocol support users to specify different types of prerequisites (e.g. dockerimage, data, and script) and then reference them in each task role. We consider prerequisites as sharable parts in the job protocol. For example, one dataset can be defined as a prerequisite, and can be used by multiple jobs.

Here's one example to use prerequisites:

protocolVersion: 2
name: test_prerequisites
type: job
jobRetryCount: 0
  - type: script
    name: install-git
      - event: taskStarts
          - apt update
          - apt install -y  git
  - type: data
    name: covid-19-data
      - event: taskStarts
          - mkdir -p /dataset/covid-19
          - >-
            git clone
  - type: dockerimage
    uri: 'ubuntu:18.04'
    name: docker_image_0
    instances: 1
      minFailedInstances: 1
    taskRetryCount: 0
      - install-git
      - covid-19-data
    dockerImage: docker_image_0
      gpu: 1
      cpu: 3
      memoryMB: 29065
      - ls -la /dataset/covid-19
  virtualCluster: default
    - plugin: ssh
        jobssh: true

In the top-level prerequisites field, we define two prerequisites: one is install-git, and the other is covid-19-data. covid-19-data downloads a dataset to the folder /dataset/covid-19. install-git is a prerequisites to install git.

In the taskRoles.taskrole.prerequisites field, we reference the two prerequisites in such order: 1. install-git 2. covid-19-data. Thus install-git will be executed before covid-19-data when the corresponding task starts. After the two prerequisites are executed, the user will be able to use the dataset in /dataset/covid-19.

The full spec is as follows:

  - name: string # required, unique name to find the prerequisite (from local or marketplace)
    type: "dockerimage | script | data | output" # for survey purpose (except dockerimage), useless for backend
    plugin: string # optional, the executor to handle current prerequisite; only support for now
    require: [] # optional, other prerequisites on which the current one depends; will be parsed by backend automatically
    failurePolicy: "ignore | fail" # optional, same default as runtime plugin
    uri: string | array # optional, for backward compatibility
    # plugin-specific properties
    # Other parameters for the plugin can be inserted here.
    # For example, "callbacks" is a parameter for

    prerequisites: # specified prerequisites will be used in the task role.
      - prerequisite-1 # on taskStarts, will execute in order
      - prerequisite-2 # on taskSucceeds, will execute in reverse order

In the future, OpenPAI will provide a convenient way to manage and share different kinds of prerequisites among cluster users.

Distributed Job Examples

TensorFlow CIFAR10

This example is a TensorFlow CIFAR-10 training job, which runs a parameter server and a worker. This job needs at least 5 GPUs. Please refer to tensorflow-cifar10.yaml.

Horovod PyTorch

This example, horovod-pytorch-synthetic-benchmark.yaml, is a Horovod benchmark using PyTorch and Open MPI. Please make sure the IFNAME setting in the job yaml fits your environment. It needs at least 8 GPUs.

InfiniBand Jobs

Here's an example for an InfiniBand job:

protocolVersion: 2
name: horovod_pytorch
type: job
version: horovod0.16.4-tf1.12.0-torch1.1.0-mxnet1.4.1-py3.5
contributor: OpenPAI
description: |
  This is a distributed synthetic benchmark for Horovod with the PyTorch backend running on OpenPAI.
  It runs [Horovod with Open MPI](
  model: resnet50
  batchsize: 64
  # Make sure IFNAME fits the node
  NCCL options for InfiniBand
  nccl: >-
    -x NCCL_IB_HCA=mlx5_0:1
  - protocolVersion: 2
    name: horovod_official
    type: dockerimage
    contributor : Horovod
    uri : horovod/horovod:0.16.4-tf1.12.0-torch1.1.0-mxnet1.4.1-py3.5
    instances: 1
      minSucceededInstances: 1
    dockerImage: horovod_official
      cpu: 16
      memoryMB: 16384
      gpu: 4
      infiniband: true
      - sleep 10
      - >
        mpirun --allow-run-as-root
        -np 8 -H master-0:4,worker-0:4
        -bind-to none -map-by slot
        -mca pml ob1
        -mca btl ^openib
        -mca btl_tcp_if_exclude lo,docker0
        <% $parameters.nccl %>
        -x PATH -x LD_LIBRARY_PATH
        --model <% $parameters.model %>
        --batch-size <% $parameters.batchsize %>
    instances: 1
    dockerImage: horovod_official
      cpu: 16
      memoryMB: 16384
      gpu: 4
      - sleep infinity
    - plugin: ssh
        jobssh: true
        sshbarrier: true

Make sure the InfiniBand driver has been installed successfully on the worker nodes, and HCA name and network interface name are set correctly.