fix(vllm): accept --disable-log-requests as no-op for vLLM 0.17+ compat

[lilyz-ai]

Summary

• --disable-log-requests was removed from vLLM's arg parser in v0.17+
• model-engine hardcodes this flag when launching vllm_server.py, causing startup failures with unrecognized arguments: --disable-log-requests
• Fix: check if the flag already exists before adding it, so this is a no-op when vLLM already handles it and a backward-compat shim when it doesn't

Test plan

• Deployed qwen3-5-27b and qwen3-5-0-8b endpoints with vLLM 0.17.0-rc1 image — both confirmed 3/3 Running

🤖 Generated with Claude Code

Greptile Summary

This PR fixes a startup crash introduced when vLLM v0.17+ removed --disable-log-requests from its argument parser, while model-engine still unconditionally passes the flag (e.g. from llm_model_endpoint_use_cases.py when sensitive_log_mode is set, and in vllm_batch.py). The fix adds a guard in parse_args that injects a no-op argument definition only when vLLM has not already registered the flag — preserving forward compatibility on older vLLM versions while preventing unrecognized arguments errors on 0.17+.

• The guard logic is correct: checks vLLM's own parser first, adds the shim only when needed.
• The fix uses parser._actions (a private argparse attribute) for the existence check; parser._option_string_actions would be a more direct and equally idiomatic alternative.
• The comment labels this "older model-engine versions pass --disable-log-requests", but the current model-engine codebase still passes this flag unconditionally (e.g. llm_model_endpoint_use_cases.py:997, vllm_batch.py:179), so the wording is mildly misleading about the longevity of this shim.
• There are no new tests added, but the PR description notes manual endpoint verification with vLLM 0.17.0-rc1.

Confidence Score: 4/5

• Safe to merge — the guard logic is correct and the fix directly addresses the vLLM 0.17+ startup failure.
• The change is small, well-scoped, and logically correct. The only minor concern is using the private parser._actions attribute instead of the more direct parser._option_string_actions, which is a style nit rather than a correctness issue. The sensitive_log_mode behavioral regression (noted in a previous review thread) is the more substantive open question but is pre-existing and outside the scope of this fix.
• No files require special attention beyond the already-discussed sensitive_log_mode behavioral gap.

Important Files Changed

Filename	Overview
model-engine/model_engine_server/inference/vllm/vllm_server.py	Adds a backward-compat shim to accept --disable-log-requests as a no-op when vLLM 0.17+ has removed the flag from its parser; uses private parser._actions for the existence check.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[vllm_server.py starts] --> B[FlexibleArgumentParser created]
    B --> C[make_arg_parser populates parser\nwith vLLM's known flags]
    C --> D{Is --disable-log-requests\nalready in parser._actions?}
    D -- Yes\nvLLM < 0.17 → vLLM handles it natively --> E[Skip — no-op shim not needed]
    D -- No\nvLLM 0.17+ removed the flag --> F[Add --disable-log-requests\nas no-op argument]
    E --> G[parser.parse_args\naccepts --disable-log-requests]
    F --> G
    G --> H[vllm_server launches successfully]

    I[llm_model_endpoint_use_cases.py\nif sensitive_log_mode:\n  vllm_args.disable_log_requests = True] -->|passes --disable-log-requests\nat runtime| A

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Prompt To Fix All With AI

This is a comment left during a code review.
Path: model-engine/model_engine_server/inference/vllm/vllm_server.py
Line: 29

Comment:
**Accessing private `_actions` attribute**

`parser._actions` is a private, underscore-prefixed attribute of Python's `ArgumentParser`. While it is effectively stable across CPython versions and widely used for introspection, it is not part of the public API and could break with future argparse or `FlexibleArgumentParser` changes.

A more robust way to check if the flag is already registered is to inspect `parser._option_string_actions` (which is a dict keyed by flag string and is equally stable in practice) or to use a try/except approach:

```suggestion
    if "--disable-log-requests" not in parser._option_string_actions:
```

`_option_string_actions` is a direct `O(1)` dict lookup that maps each flag string (e.g. `"--disable-log-requests"`) to its `Action`, which is both more efficient and slightly more explicit than iterating over `_actions`.

How can I resolve this? If you propose a fix, please make it concise.

_{Last reviewed commit: "Merge branch 'main' ..."}

Context used:

• Rule used - Add comments to explain complex or non-obvious log... (source)

Learnt From
scaleapi/scaleapi#126958

[greptile-apps]

Silent no-op may break sensitive_log_mode compliance guarantees

The comment says "older model-engine versions pass --disable-log-requests", but the current model-engine code (llm_model_endpoint_use_cases.py:996-997) still hardcodes this flag whenever hmi_config.sensitive_log_mode is True:

if hmi_config.sensitive_log_mode:
    vllm_args.disable_log_requests = True

By silently accepting --disable-log-requests as a no-op in vLLM 0.17+, request logging will not be disabled for endpoints that have sensitive_log_mode set. If sensitive_log_mode is used for privacy or compliance reasons, this silent behavioral regression could expose request-level logs that were previously suppressed.

It would be worth either:

1. Confirming that vLLM 0.17+ disables request logging by default (or via a different mechanism) and documenting that here, or
2. Identifying the replacement mechanism in vLLM 0.17+ (e.g., a new flag or VLLM_CONFIGURE_LOGGING env var) and wiring sensitive_log_mode through that path alongside this no-op shim.

Prompt To Fix With AI

This is a comment left during a code review.
Path: model-engine/model_engine_server/inference/vllm/vllm_server.py
Line: 26-36

Comment:
**Silent no-op may break `sensitive_log_mode` compliance guarantees**

The comment says "older model-engine versions pass `--disable-log-requests`", but the *current* model-engine code (`llm_model_endpoint_use_cases.py:996-997`) still hardcodes this flag whenever `hmi_config.sensitive_log_mode` is `True`:

```python
if hmi_config.sensitive_log_mode:
    vllm_args.disable_log_requests = True
```

By silently accepting `--disable-log-requests` as a no-op in vLLM 0.17+, request logging will **not** be disabled for endpoints that have `sensitive_log_mode` set. If `sensitive_log_mode` is used for privacy or compliance reasons, this silent behavioral regression could expose request-level logs that were previously suppressed.

It would be worth either:
1. Confirming that vLLM 0.17+ disables request logging by default (or via a different mechanism) and documenting that here, or
2. Identifying the replacement mechanism in vLLM 0.17+ (e.g., a new flag or `VLLM_CONFIGURE_LOGGING` env var) and wiring `sensitive_log_mode` through that path alongside this no-op shim.

How can I resolve this? If you propose a fix, please make it concise.