Run on an on-prem cluster (intermediate)¶
Audience: Users who need to run on an academic or enterprise private cluster.
Setup the cluster¶
This guide shows how to run a training job on a general purpose cluster. We recommend beginners to try this method first because it requires the least amount of configuration and changes to the code. To setup a multi-node computing cluster you need:
Multiple computers with PyTorch Lightning installed
A network connectivity between them with firewall rules that allow traffic flow on a specified MASTER_PORT.
Defined environment variables on each node required for the PyTorch Lightning multi-node distributed training
PyTorch Lightning follows the design of PyTorch distributed communication package. and requires the following environment variables to be defined on each node:
MASTER_PORT - required; has to be a free port on machine with NODE_RANK 0
MASTER_ADDR - required (except for NODE_RANK 0); address of NODE_RANK 0 node
WORLD_SIZE - required; how many nodes are in the cluster
NODE_RANK - required; id of the node in the cluster
Setup the training script¶
To train a model using multiple nodes, do the following:
Design your LightningModule (no need to add anything specific here).
Enable DDP in the trainer
# train on 32 GPUs across 4 nodes trainer = Trainer(accelerator="gpu", devices=8, num_nodes=4, strategy="ddp")
Submit a job to the cluster¶
To submit a training job to the cluster you need to run the same training script on each node of the cluster. This means that you need to:
Copy all third-party libraries to each node (usually means - distribute requirements.txt file and install it).
Copy all your import dependencies and the script itself to each node.
Run the script on each node.
Debug on a cluster¶
When running in DDP mode, some errors in your code can show up as an NCCL issue.
NCCL_DEBUG=INFO environment variable to see the ACTUAL error.
NCCL_DEBUG=INFO python train.py ...
Setting up a cluster for distributed training is not trivial. Lightning offers lightning-grid which allows you to configure a cluster easily and run experiments via the CLI and web UI.
Try it out for free today: