fix: Restore running single-process without etcd

[grahamking]

I missed this in my review of #2011.

Creating a DistributedRuntime connects to etcd. When #2011 moved it up to the top of the function that meant that dynamo-run <model>, with no distributed system parts, would still try to connect to etcd.

This PR moves creating the Distributed Runtime back into the EngineConfig::Dynamic section, which is the only part that should talk to etcd.

Summary by CodeRabbit

• Refactor
  • Improved the initialization sequence of the HTTP service to ensure all configuration is applied before the service starts. No changes to user-facing features or behavior.

[coderabbitai]

Walkthrough

The refactoring alters the initialization sequence of the HTTP service within the run function. The HTTP service builder is now configured with shared parameters first, and the actual building of the service is deferred until after engine-specific configuration within each match arm. This centralizes and conditions the build step based on the engine configuration variant.

Changes

Cohort / File(s)	Change Summary
HTTP Service Initialization Refactor lib/llm/src/entrypoint/input/http.rs	Refactored the HTTP service construction in the run function to defer building the service until after engine-specific configuration. The builder is now fully configured within each match arm before building and returning the service. No public API changes.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~7 minutes

Poem

A builder waits, its work deferred,
Until the engine's path is heard.
With branches split and setup done,
The service builds and then will run.
A rabbit hops through code so neat—
Refactoring makes the flow complete! 🐇✨

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📥 Commits

Reviewing files that changed from the base of the PR and between dbe48a1 and 03d2fe6.

📒 Files selected for processing (1)

• lib/llm/src/entrypoint/input/http.rs (4 hunks)

🧰 Additional context used

🧠 Learnings (1)

📚 Learning: the asyncenginecontextprovider trait in lib/runtime/src/engine.rs was intentionally changed from `se...

Learnt from: ryanolson
PR: ai-dynamo/dynamo#1919
File: lib/runtime/src/engine.rs:168-168
Timestamp: 2025-07-14T21:25:56.930Z
Learning: The AsyncEngineContextProvider trait in lib/runtime/src/engine.rs was intentionally changed from `Send + Sync + Debug` to `Send + Debug` because the Sync bound was overly constraining. The trait should only require Send + Debug as designed.

Applied to files:

• lib/llm/src/entrypoint/input/http.rs

⏰ 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). (3)

• GitHub Check: Build and Test - vllm
• GitHub Check: pre-merge-rust (.)
• GitHub Check: pre-merge-rust (lib/bindings/python)

🔇 Additional comments (8)

lib/llm/src/entrypoint/input/http.rs (8)

23-28: LGTM: Proper deferred service building setup.

The refactoring correctly creates a mutable HTTP service builder with shared configuration parameters, deferring the actual service building until after engine-specific setup. This enables conditional configuration based on the engine variant.

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30-36: LGTM: Enables single-process mode without etcd.

The Dynamic engine configuration now properly handles the case where etcd is not available. The etcd client is conditionally added to the builder only if present, and the service is built after this configuration. This directly addresses the PR objective of restoring single-process mode without requiring etcd.

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55-55: LGTM: Consistent return pattern.

The Dynamic variant correctly returns the built HTTP service to match the new pattern where each engine variant returns the configured service.

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61-63: LGTM: Proper service building for StaticRemote.

The StaticRemote variant correctly builds the HTTP service after setting up the distributed runtime but before model registration. This maintains the logical flow while conforming to the new deferred building pattern.

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101-101: LGTM: Consistent return pattern.

The StaticRemote variant correctly returns the built HTTP service.

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104-109: LGTM: Proper service building for StaticFull.

The StaticFull variant correctly builds the HTTP service before model registration and returns it consistently with the new pattern.

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116-132: LGTM: Proper service building for StaticCore.

The StaticCore variant correctly builds the HTTP service before pipeline creation and model registration, then returns it consistently with the new pattern.

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134-134: LGTM: Clean match expression assignment.

The match expression now cleanly assigns the result to http_service, maintaining the same variable name and usage pattern as before the refactoring.

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