The examples below run on the torchelastic/examples Docker image, built from the examples/Dockerfile.


The $VERSION (e.g. 0.2.0) variable is used throughout this page, this should be substituted with the version of torchelastic you are using. The examples below only work on torchelastic >=0.2.0.


  1. (recommended) Instance with GPU(s)

  2. Docker

  3. NVIDIA Container Toolkit

  4. export VERSION=<torchelastic version>


PyTorch data loaders use shm. The default docker shm-size is not large enough and will OOM when using multiple data loader workers. You must pass --shm-size to the docker run command or set the number of data loader workers to 0 (run on the same process) by passing the appropriate option to the script (use the --help flag to see all script options). In the examples below we set --shm-size.

Classy Vision

Classy Vision is an end-to-end framework for image and video classification built on PyTorch. It works out-of-the-box with torchelastic’s launcher.

Launch two trainers on a single node:

docker run --shm-size=2g torchelastic/examples:$VERSION
           --config_file /workspace/classy_vision/configs/template_config.json

If you have an instance with GPUs, run a worker on each GPU:

docker run --shm-size=2g --gpus=all torchelastic/examples:$VERSION
           --config_file /workspace/classy_vision/configs/template_config.json



an instance with at least one GPU is required for this example

Launch $NUM_CUDA_DEVICES number of workers on a single node:

docker run --shm-size=2g --gpus=all torchelastic/examples:$VERSION
           --arch resnet18
           --epochs 20
           --batch-size 32


We now show how to use the PyTorch Elastic Trainer launcher to start a distributed application spanning more than one container. The application is intentionally kept “bare bones” since the objective is to show how to create a torch.distributed.ProcessGroup instance. Once a ProcessGroup is created, you can use any functionality needed from the torch.distributed package.

The docker-compose.yml file is based on the example provided with the Bitnami ETCD container image.

Obtaining the example repo

Clone the PyTorch Elastic Trainer Git repo using

git clone

make an environment variable that points to the elastic repo, e.g.

export TORCHELASTIC_HOME=~/elastic

Building the samples Docker container

While you can run the rest of this example using a pre-built Docker image, you can also build one for yourself. This is especially useful if you would like to customize the image. To build the image, run:

cd $TORCHELASTIC_HOME && docker build -t hello_elastic:dev .

Running an existing sample

This example uses docker-compose to run two containers: one for the ETCD service and one for the sample application itself. Docker compose takes care of all aspects of establishing the network interfaces so the application container can communicate with the ETCD container.

To start the example, run

cd $TORCHELATIC_HOME/examples/multi_container && docker-compose up

You should see two sets of outputs, one from ETCD starting up and one from the application itself. The output from the application looks something like this:

example_1      | INFO 2020-04-03 17:36:31,582 Etcd machines: ['http://etcd-server:2379']
example_1      | *****************************************
example_1      | Setting OMP_NUM_THREADS environment variable for each process to be 1 in default, to avoid your system being overloaded, please further tune the variable for optimal performance in your application as needed.
example_1      | *****************************************
example_1      | INFO 2020-04-03 17:36:31,922 Attempting to join next rendezvous
example_1      | INFO 2020-04-03 17:36:31,929 New rendezvous state created: {'status': 'joinable', 'version': '1', 'participants': []}
example_1      | INFO 2020-04-03 17:36:32,032 Joined rendezvous version 1

The high-level differences between a single-container vs multi-container launches are:

  1. Specify --nnodes=$MIN_NODE:$MAX_NODE instead of --nnodes=1.

  2. An etcd server must be setup before starting the worker containers.

  3. Remove --standalone and specify --rdzv_backend, --rdzv_endpoint and --rdzv_id.

For more information see elastic launch.


The multi-node, multi-worker case is similar to running multi-container, multi-worker. Simply run each container on a separate node, occupying the entire node. Alternatively, you can use our kubernetes elastic job controller to launch a multi-node job.


We recommend you setup a highly available etcd server when deploying multi-node jobs in production as this is the single point of failure for your jobs. Depending on your usecase you can either sidecar an etcd server with each job or setup a shared etcd server. If etcd does not meet your requirements you can implement your own rendezvous handler and use our APIs to create a custom launcher.


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