[AIDynamo] prefill-worker disabled excessive config

[podkidyshev]

Summary

For aggregated topologies, we set prefill_worker.num-nodes = 0 because no prefill worker process is launched. CloudAI still requires cmd and worker-initialized-regex for that worker block, even though they are never used. It would be cleaner if these fields were optional whenever num-nodes = 0.

Example of config clutter we have today:

[cmd_args.dynamo.prefill_worker]
num-nodes = 0
cmd = 'python3 -m dynamo.vllm --is-prefill-worker'
worker-initialized-regex = 'VllmWorker.*has.been.initialized'

What is should be:

[cmd_args.dynamo.prefill_worker]
num-nodes = 0

Test Plan

• Automated CI
• Regression test: conf/experiments/ai_dynamo/test_scenario/vllm_slurm.toml
• Config with the new functionality

TOML

name = "dynamo-zero-prefill-slurm"
job_status_check = false

[[Tests]]
id = "test.aggregated.vllm-zero-prefill"
name = "vllm-zero-prefill"
description = "Aggregated vLLM smoke test with no prefill launch fields."
test_template_name = "AIDynamo"
num_nodes = 1
time_limit = "00:10:00"
extra_container_mounts = ["/run/udev:/run/udev"]

  [Tests.cmd_args]
  docker_image_url = "nvcr.io/nvidia/ai-dynamo/vllm-runtime:1.1.1"
  workloads = "aiperf.sh"

    [Tests.cmd_args.dynamo]
    backend = "vllm"
    model = "Qwen/Qwen3-0.6B"
    ingress-cmd = "python -m dynamo.frontend --router-mode kv --router-reset-states"

      [Tests.cmd_args.dynamo.prefill_worker]
      num-nodes = 0

      [Tests.cmd_args.dynamo.decode_worker]
      num-nodes = 1
      cmd = "python3 -m dynamo.vllm"
      worker-initialized-regex = "VllmWorker.*has.been.initialized"
      extra-args = "--no-enable-expert-parallel"

        [Tests.cmd_args.dynamo.decode_worker.args]
        gpu-memory-utilization = 0.8
        tensor-parallel-size = 4
        pipeline-parallel-size = 1

    [Tests.cmd_args.aiperf.args]
    concurrency = 1
    endpoint-type = "chat"
    extra-inputs = '{"min_tokens":10}'
    output-tokens-mean = 32
    request-count = 10
    server-metrics = "auto"
    streaming = true
    synthetic-input-tokens-mean = 128

  [Tests.extra_env_vars]
  UCX_LOG_LEVEL = "warn"
  HF_HUB_OFFLINE = "0"
  TRANSFORMERS_OFFLINE = "0"
  HF_DATASETS_OFFLINE = "0"
  DYNAMO_NODELIST = "$(scontrol show hostname $SLURM_JOB_NODELIST | tr -s '\\n' ',')"
  UCX_TLS = "all"

[[Tests]]
id = "test.aggregated.sglang-zero-prefill"
name = "sglang-zero-prefill"
description = "Aggregated SGLang smoke test with no prefill launch fields."
test_template_name = "AIDynamo"
num_nodes = 1
time_limit = "00:10:00"
extra_container_mounts = ["/run/udev:/run/udev"]

  [Tests.cmd_args]
  docker_image_url = "nvcr.io/nvidia/ai-dynamo/sglang-runtime:1.1.1"
  workloads = "aiperf.sh"

    [Tests.cmd_args.dynamo]
    backend = "sglang"
    model = "Qwen/Qwen3-0.6B"
    endpoint = "v1/chat/completions"
    ingress-cmd = "python -m dynamo.frontend --router-mode kv --router-reset-states"
    node-setup-cmd = "hostname"

      [Tests.cmd_args.dynamo.prefill_worker]
      num-nodes = 0

      [Tests.cmd_args.dynamo.decode_worker]
      num-nodes = 1
      cmd = "python3 -m dynamo.sglang"
      worker-initialized-regex = 'register._register_model_with_runtime_config:.Successfully.registered.LLM.with.runtime.config'
      extra-args = "--trust-remote-code --skip-tokenizer-init --enable-metrics"

        [Tests.cmd_args.dynamo.decode_worker.args]
        page-size = 16
        tensor-parallel-size = 4
        pipeline-parallel-size = 1
        host = "0.0.0.0"

    [Tests.cmd_args.aiperf]
    setup-cmd = "python -m pip install --break-system-packages --ignore-installed blinker==1.9.0 && python -m pip install --break-system-packages --upgrade aiperf==0.8.0"

      [Tests.cmd_args.aiperf.args]
      concurrency = 1
      extra-inputs = '{"min_tokens":10}'
      output-tokens-mean = 32
      request-count = 10
      server-metrics = "auto"
      streaming = true
      synthetic-input-tokens-mean = 128

  [Tests.extra_env_vars]
  UCX_LOG_LEVEL = "warn"
  HF_HUB_OFFLINE = "0"
  TRANSFORMERS_OFFLINE = "0"
  HF_DATASETS_OFFLINE = "0"
  DYNAMO_NODELIST = "$(scontrol show hostname $SLURM_JOB_NODELIST | tr -s '\\n' ',')"
  UCX_TLS = "all"

Additional Notes

N/A

[coderabbitai]

📝 Walkthrough

Walkthrough

WorkerConfig now supports disabled workers without launch fields. Slurm and Kubernetes generation use explicit enabled-state checks and omit disabled prefill configuration.

Changes

Worker enablement handling

Layer / File(s)	Summary
Worker configuration validation src/cloudai/workloads/ai_dynamo/ai_dynamo.py, tests/workloads/ai_dynamo/test_command_gen_strategy_slurm.py	cmd and worker_initialized_regex are optional for zero-node workers. Enabled workers still require both fields. Tests cover validation and generated Slurm arguments.
Kubernetes worker generation src/cloudai/workloads/ai_dynamo/kubernetes_json_gen_strategy.py, tests/workloads/ai_dynamo/test_json_gen_strategy_kubernetes.py	Kubernetes generation validates worker enablement, uses worker configuration directly, and omits disabled prefill services and prefill-specific decode settings. Tests cover these cases.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: 🟡 Moderate · up to c396e

This change simplifies zero-node prefill configurations, but Kubernetes generation can still fail with list-valued node counts, and empty node lists still require launch fields even though no worker is launched. These configuration-dependent correctness issues should be addressed before the PR is merge-ready.

Suggested reviewers: jj10306

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The description clearly explains why disabled prefill workers may omit launch fields and includes relevant tests and configurations.
Title check	✅ Passed	The title identifies the AIDynamo prefill-worker configuration change and matches the main purpose of the pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ipod/dynamo-0-prefill

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[coderabbitai]

Actionable comments posted: 2

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Inline comments:
In `@src/cloudai/workloads/ai_dynamo/ai_dynamo.py`:
- Around line 144-148: Update WorkerConfig.is_enabled to return false when
num_nodes is an empty list by relying solely on whether any node count is
nonzero, while preserving enabled behavior for configured nonzero counts. Add a
regression test covering WorkerConfig(num_nodes=[]) and confirming it is
disabled without requiring worker launch settings.

In `@src/cloudai/workloads/ai_dynamo/kubernetes_json_gen_strategy.py`:
- Line 67: Resolve list-valued WorkerConfig.num_nodes to a scalar selected
trial, or reject it with a clear ValueError, before Kubernetes generation so
_set_multinode_if_needed never compares a list with an integer. Update the
decode-worker call at
src/cloudai/workloads/ai_dynamo/kubernetes_json_gen_strategy.py#L67-L67 and the
prefill-worker call at
src/cloudai/workloads/ai_dynamo/kubernetes_json_gen_strategy.py#L89-L89 to pass
scalar node counts.

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Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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Reviewing files that changed from the base of the PR and between 3369e5d and c396e14.

📒 Files selected for processing (4)

• src/cloudai/workloads/ai_dynamo/ai_dynamo.py
• src/cloudai/workloads/ai_dynamo/kubernetes_json_gen_strategy.py
• tests/workloads/ai_dynamo/test_command_gen_strategy_slurm.py
• tests/workloads/ai_dynamo/test_json_gen_strategy_kubernetes.py

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