Communication Patterns: Rendezvous
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In the context of distributed training, particularly within PyTorch, a rendezvous is a process or mechanism that facilitates the initialization and coordination of a process group for distributed communication.
When a distributed training job starts, each worker process needs to discover other workers and establish communication channels. The rendezvous mechanism handles this bootstrap process. It typically involves a central service or a well-known IP address that new processes can contact to register themselves and get information about other members of the group, such as their network addresses and ranks.
PyTorch's `torch.distributed.init_process_group`, for example, uses a rendezvous backend (like `env://` for environment variable-based discovery, or more sophisticated backends like `etcd` or `c10d`) to achieve this. The rendezvous ensures that all processes agree on the group membership and can synchronize their initial state before training begins. This is a critical first step for any distributed operation, as it sets up the foundation for collective communications and data exchange.
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