YARN Pluggable Device Framework

Introduction

At present, YARN supports GPU/FPGA device through a native, coupling way. But it's difficult for a vendor to implement such a device plugin because the developer needs to understand various integration points with YARN and also a deeper understanding YARN internals related to NodeManager.

Pain Points Of Current Device Plugin

Some of the pain points for current device plugin development and integration are listed below:

At least 6 classes to be implemented (If you wanna support Docker, you’ll implement one more “DockerCommandPlugin”).
When implementing the “ResourceHandler” interface, the developer must understand the YARN NM internal concepts like container launch mechanism, cgroups operations, docker runtime operations.
If one wants isolation, the native container-executor also need a new module written in C language.

This brings burdens to the community to maintain both YARN core and vendor-specific code. For more details, check YARN-8851 design document.

Based on the above reasons and in order for YARN and vendor-specific plugin to evolve independently, we developed a new pluggable device framework to ease vendor device plugin development and provide a more flexible way to integrate with YARN.

Quick Start

This pluggable device framework not only simplifies the plugin development but also the number of configurations in YARN which are needed for plugin integration. Before we go through how to implement your own device plugin, let's first see how to use an existing plugin.

As an example, the new framework includes a sample implementation of Nvidia GPU plugin supporting detecting Nvidia GPUs, the custom scheduler and isolating containers run with both YARN cgroups and Nvidia Docker runtime v2.

Prerequisites

The pluggable device framework depends on LinuxContainerExecutor to handle resource isolation and Docker stuff. So LCE and Docker enabled on YARN is a must. See Using CGroups with YARN and Docker on YARN
The sample plugin NvidiaGPUPluginForRuntimeV2 requires Nvidia GPU drivers and Nvidia Docker runtime v2 installed in the nodes. See Nvidia official documents for this.
If you use YARN capacity scheduler, below DominantResourceCalculator configuration is needed (In capacity-scheduler.xml):

<property>
  <name>yarn.scheduler.capacity.resource-calculator</name>
  <value>org.apache.hadoop.yarn.util.resource.DominantResourceCalculator</value>
</property>

Enable Device Plugin Framework

Two properties to enable the pluggable framework support. First one is in yarn-site.xml:

<property>
  <name>yarn.nodemanager.pluggable-device-framework.enabled</name>
  <value>true</value>
</property>

And then enable the isolation native module in container-executor.cfg:

# The configs below deal with settings for resource handled by pluggable device plugin framework
[devices]
  module.enabled=true
#  devices.denied-numbers=## Blacklisted devices not permitted to use. The format is comma separated "majorNumber:minorNumber". For instance, "195:1,195:2". Leave it empty means default devices reported by device plugin are all allowed.

Configure Sample Nvidia GPU Plugin

The pluggable device framework loads one plugin and talks to it to know which resource name the plugin is handling. And the resource name should be pre-defined in resource-types.xml. Here we already know the resource name is nvidia.com/gpu from the plugin implementation.

<property>
  <name>yarn.resource-types</name>
  <value>nvidia.com/gpu</value>
</property>

After define the resource name handled by the plugin. We can configure the plugin name in `yarn-site.xml now:

<property>
  <name>yarn.nodemanager.pluggable-device-framework.device-classes</name>
  <value>org.apache.hadoop.yarn.server.nodemanager.containermanager.resourceplugin.com.nvidia.NvidiaGPUPluginForRuntimeV2</value>
</property>

Note that the property value must be a full class name of the plugin.

Restart YARN And Run Job

After restarting YARN, you should see the nvidia.com/gpu resource count displayed while accessing YARN UI2 Overview and NodeManages page or issuing command:

yarn node -list -showDetails

Then you can run job requesting several nvidia.com/gpu as usual:

yarn jar <path/to/hadoop-yarn-applications-distributedshell.jar> \
       -jar <path/to/hadoop-yarn-applications-distributedshell.jar> \
       -shell_env YARN_CONTAINER_RUNTIME_TYPE=docker \
       -shell_env YARN_CONTAINER_RUNTIME_DOCKER_IMAGE=<docker-image-name> \
       -shell_command nvidia-smi \
       -container_resources memory-mb=3072,vcores=1,nvidia.com/gpu=2 \
       -num_containers 2

NM API To Query Resource Allocation

When a job run with resource like nvidia.com/gpu, you can query a NM node's resource allocation through below RESTful API. Note that the resource name should be URL encoded format (in this case, "nvidia.com%2Fgpu").

node:port/ws/v1/node/resources/nvidia.com%2Fgpu

For instance, use below command to get the JSON format resource allocation:

curl localhost:8042/ws/v1/node/resources/nvidia.com%2Fgpu | jq .

Develop Your Own Plugin

Configure an existing plugin is easy. But how about implementing my own one? It's easy too! See Develop Device Plugin

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