fix: KeyError in kv_router.py by Initializing active_blocks_dict for New Workers

[umang-kedia-hpe]

Overview:
This pull request addresses a potential KeyError in the kv_router.py component by ensuring that the active_blocks_dict is properly initialized for new worker_id entries. This improves the robustness of the router when handling dynamic worker registration and prevents runtime errors during distributed inference.

Details:
Updated the _update_and_get_active_blocks method in kv_router.py to check if a worker_id is present in active_blocks_dict.

If the worker_id is not present, it initializes the entry with the current polled_value for both old_value and predictive_value.
This change prevents KeyError exceptions when new workers are added dynamically or when the router encounters previously unseen worker IDs.

Where should the reviewer start?
Review the changes in examples/llm/components/kv_router.py, specifically the _update_and_get_active_blocks method.

Summary by CodeRabbit

• Bug Fixes
  • Improved handling of missing worker entries to prevent errors and ensure proper initialization when new workers are encountered.

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[github-actions]

👋 Hi umang-kedia-hpe! Thank you for contributing to ai-dynamo/dynamo.

Just a reminder: The NVIDIA Test Github Validation CI runs an essential subset of the testing framework to quickly catch errors.Your PR reviewers may elect to test the changes comprehensively before approving your changes.

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Walkthrough

The method _update_and_get_active_blocks in kv_router.py was updated to properly handle cases where a worker_id is not present in the active_blocks_dict. The method now initializes missing entries to avoid key errors and ensure correct behavior on first access.

Changes

File	Change Summary
examples/llm/components/kv_router.py	Enhanced _update_and_get_active_blocks to initialize missing worker_id entries in the dictionary.

Poem

A rabbit hopped through code so bright,
Ensuring keys were set just right.
No more errors in the night,
When workers new appear in sight.
With careful hops, the bug took flight!
🐇✨

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📥 Commits

Reviewing files that changed from the base of the PR and between 6835dd7 and b0b88c7.

📒 Files selected for processing (1)

• examples/llm/components/kv_router.py (1 hunks)

🧰 Additional context used

🧠 Learnings (2)

📓 Common learnings

Learnt from: alec-flowers
PR: ai-dynamo/dynamo#1181
File: lib/llm/src/kv_router/publisher.rs:379-425
Timestamp: 2025-05-29T00:02:35.018Z
Learning: In lib/llm/src/kv_router/publisher.rs, the functions `create_stored_blocks` and `create_stored_block_from_parts` are correctly implemented and not problematic duplications of existing functionality elsewhere in the codebase.

Learnt from: PeaBrane
PR: ai-dynamo/dynamo#1285
File: lib/llm/src/kv_router/scheduler.rs:260-266
Timestamp: 2025-05-30T06:34:12.785Z
Learning: In the KV router scheduler code, PeaBrane prefers fail-fast behavior over silent failure handling. When accessing worker metrics data that could be out-of-bounds (like dp_rank indexing), explicit panics are preferred over graceful degradation with continue statements to ensure data integrity issues are caught early.

examples/llm/components/kv_router.py (1)

Learnt from: alec-flowers
PR: ai-dynamo/dynamo#1181
File: lib/llm/src/kv_router/publisher.rs:379-425
Timestamp: 2025-05-29T00:02:35.018Z
Learning: In lib/llm/src/kv_router/publisher.rs, the functions `create_stored_blocks` and `create_stored_block_from_parts` are correctly implemented and not problematic duplications of existing functionality elsewhere in the codebase.

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (2)

• GitHub Check: pre-commit
• GitHub Check: Build and Test - vllm

🔇 Additional comments (1)

examples/llm/components/kv_router.py (1)

188-191: LGTM! Proper initialization prevents KeyError for dynamic workers.

This fix correctly addresses the core issue by initializing missing worker entries in active_blocks_dict. The approach of setting both old_value and predictive_value to polled_value is appropriate for new workers, ensuring consistent behavior on first access.

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[PeaBrane]

@umang-kedia-hpe thanks for your contribution. This is a good change
Can you add a logger.warn on a new key add, and also you may need to lint your changes (or install pre-commit) to pass our CIs

[umang-kedia-hpe]

Update:

• Added logger.warn when a new key is added.
• Ran pre-commit to lint and format the code.

Please let me know if there’s anything else I should address. Thank you for your feedback!