refactor: align multimodal example port allocation with vLLM components

[nnshah1]

Summary

• Replace dynamic port allocation with environment variable-based configuration to match components/src/dynamo/vllm/args.py approach
• Remove runtime.allocate_port_block() in favor of DYN_VLLM_KV_EVENT_PORT environment variable
• Simplify port management to be consistent across the codebase

Changes Made

Port Allocation Strategy

• Removed dynamic port allocation via runtime.allocate_port_block()
• Added environment variable-based configuration using DYN_VLLM_KV_EVENT_PORT
• Added port validation with registered port range (1024-49151)

Configuration Functions

• Updated configure_ports() to be synchronous and use environment variables
• Added create_kv_events_config() function to match VLLM components pattern
• Updated overwrite_args() to follow the same structure as VLLM components

Host Management

• Added ensure_side_channel_host() and get_host_ip() functions
• Removed the set_side_channel_host_and_port() function
• Updated to only set host (not port) for NIXL side channel

Code Structure

• Removed all port allocation metadata tracking
• Simplified Config class by removing side_channel_port field
• Updated worker.py to call non-async configure_ports(config)

Test plan

• Verify multimodal examples still work with environment variable port configuration
• Test that DYN_VLLM_KV_EVENT_PORT environment variable is properly respected
• Confirm NIXL side channel host resolution works correctly
• Validate port range validation (1024-49151) functions as expected

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Updated port configuration mechanism to use environment-driven allocation instead of runtime-based allocation, simplifying port management for multimodal examples.
  • Refined side-channel host management with improved default handling and fallback logic.
  • Streamlined configuration by removing unnecessary side-channel port-related settings and adding conditional port requirements based on feature enablement.

[coderabbitai]

Walkthrough

Port configuration logic is refactored across two files. The async port allocation mechanism is replaced with synchronous environment-driven retrieval. Function signatures are updated, and the Config class no longer holds side_channel_port. Several port-allocation functions are removed and replaced with new configuration helpers.

Changes

Cohort / File(s)	Change Summary
Port Configuration API Refactoring examples/multimodal/utils/args.py	Replaced async port allocation with synchronous get_kv_port() function using environment variables. Removed side_channel_port field from Config class and functions allocate_and_reserve_port() and set_side_channel_host_and_port(). Added ensure_side_channel_host() helper, configure_ports(config) function, and DEFAULT_ENDPOINT constant. Updated overwrite_args to conditionally require kv_port only when enable_prefix_caching is enabled.
Port Configuration Call Site examples/multimodal/components/worker.py	Updated configure_ports() invocation from await configure_ports(runtime, config) to configure_ports(config), removing the runtime parameter and eliminating the await keyword.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

• Verify async-to-sync conversion is correct and does not introduce race conditions
• Validate environment variable fallback logic (particularly in get_kv_port() and ensure_side_channel_host())
• Confirm all call sites of removed functions (allocate_and_reserve_port, set_side_channel_host_and_port) are updated or no longer needed
• Check that conditional kv_port requirement logic in overwrite_args correctly gates on enable_prefix_caching
• Ensure DEFAULT_ENDPOINT usage is consistent throughout the codebase

Poem

🐰 Ports once danced in async dreams so grand,
Now environment speaks, a simpler plan!
No more runtime queues, just variables bright,
Configuration flows—synchronous and light! ✨

Pre-merge checks

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main refactoring change: aligning multimodal example port allocation with vLLM components, which is the core objective of the PR.
Description check	✅ Passed	The PR description comprehensively covers all template sections including overview, detailed changes, and related context, though it doesn't reference a specific GitHub issue.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[coderabbitai]

Actionable comments posted: 1

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

examples/multimodal/utils/args.py (1)

139-170: Fix missing kv_port initialization when prefix caching default is None

AsyncEngineArgs.enable_prefix_caching comes out of CLI parsing as None until vLLM applies its defaults.(docs.vllm.ai) With the new synchronous flow, that falsy value skips the configure_ports branch and leaves config.kv_port unset. As soon as overwrite_args formats the ZMQ endpoint, config.kv_port - dp_rank raises a TypeError, so the worker never starts.

Set config.kv_port before we build the defaults by treating None as “we will enable prefix caching” (which matches the V1 default) and assigning the port eagerly.

 def configure_ports(config: Config):
     """Configure port settings from dedicated environment overrides."""
 
-    if config.engine_args.enable_prefix_caching:
-        config.kv_port = get_kv_port()
+    enable_prefix = config.engine_args.enable_prefix_caching
+    if enable_prefix is None:
+        enable_prefix = True
+        config.engine_args.enable_prefix_caching = True
+
+    if enable_prefix:
+        config.kv_port = get_kv_port()
 
     ensure_side_channel_host()

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📥 Commits

Reviewing files that changed from the base of the PR and between e0fb52d and 0c3cae8.

📒 Files selected for processing (2)

• examples/multimodal/components/worker.py (1 hunks)
• examples/multimodal/utils/args.py (1 hunks)

🧰 Additional context used

🧬 Code graph analysis (2)

examples/multimodal/components/worker.py (1)

examples/multimodal/utils/args.py (1)

• configure_ports (139-145)

examples/multimodal/utils/args.py (4)

lib/bindings/python/examples/hello_world/server_sglang_static.py (1)

• Config (31-37)

lib/bindings/python/examples/hello_world/server_sglang.py (1)

• Config (40-46)

lib/bindings/python/examples/hello_world/server_sglang_tok.py (1)

• Config (43-49)

lib/bindings/python/examples/hello_world/server_vllm.py (1)

• Config (52-58)

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