PMLE Scaling Prototypes into ML Models Practice Question
Your PyTorch training script uses DistributedDataParallel (DDP) across 4 vertices each with 4 GPUs (16 GPUs total). You submit a Vertex AI custom training job. How should you configure the worker pool spec?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create one worker pool with 4 replicas, each with machine type having 4 GPUs
For DDP across multiple machines, use MultiWorkerMirroredStrategy equivalent in PyTorch: set replicas to 4, each with machine type having 4 GPUs. The TF_CONFIG env var is not needed; Vertex AI sets necessary environment variables for distributed training.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Create one worker pool with 4 replicas, each with machine type having 4 GPUs
Why this is correct
This matches the requirement: 4 workers, each with 4 GPUs.
- ✗
Create a chief worker pool with 1 replica (4 GPUs) and a parameter server pool with 4 replicas (no GPUs)
Why it's wrong here
DDP does not use parameter servers; this is for TensorFlow with PS strategy.
- ✗
Create 4 separate jobs, each with 1 replica and 4 GPUs
Why it's wrong here
Separate jobs are not coordinated; DDP requires a single job with multiple workers.
- ✗
Create one worker pool with 16 replicas, each with 1 GPU
Why it's wrong here
This would create 16 single-GPU nodes, not 4x4.
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