Delay setup_model_metrics() until /metrics is called #327

umago · 2025-07-31T15:01:59Z

Description

This patch moves the setup_model_metrics() from the service startup to the first time the /metrics endpoint is called. This speed up the lightspeed-stack service initialization and also make lightspeed-stack more resilient regarding service initialization order because it no longer requires llama-stack to be started first (as setup_model_metrics() tries to connect to llama-stack and fetch the list of models from it).

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Summary by CodeRabbit

New Features
- Improved reliability of metrics setup by ensuring model metrics are initialized only once before serving metrics data.
- Updated container and deployment configuration to build the application image locally for streamlined development.
Bug Fixes
- Enhanced the /metrics endpoint to handle setup asynchronously, preventing redundant or repeated setup calls.
Tests
- Updated tests for the metrics endpoint to support asynchronous execution and verify correct setup behavior.

coderabbitai · 2025-07-31T15:02:06Z

Walkthrough

The /metrics endpoint handler was converted to an asynchronous function, now awaiting a one-time setup of model metrics using a decorated async function to ensure it runs only once. Related imports and startup logic were removed, a new decorator was introduced, and tests were updated to accommodate the asynchronous changes and verify correct execution.

Changes

Cohort / File(s)	Change Summary
/metrics Endpoint Async Refactor `src/app/endpoints/metrics.py`, `tests/unit/app/endpoints/test_metrics.py`	Converted the `/metrics` endpoint handler and its test to async functions. The handler now awaits `setup_model_metrics()`, and the test mocks and asserts its invocation.
Startup Logic Cleanup `src/app/main.py`	Removed import and invocation of `setup_model_metrics` from the application startup event.
Async Run-Once Decorator `src/utils/common.py`	Added `run_once_async` decorator to ensure an async function executes only once per process, storing and returning a single task result for all calls.
Model Metrics Setup Improvements `src/metrics/utils.py`	Decorated `setup_model_metrics` with `@run_once_async` and added logging at start and completion to control and trace one-time setup execution.
Container Build and Deployment Updates `Containerfile`, `docker-compose.yaml`	Modified `uv sync` command by removing `--no-install-project` flag; changed `lightspeed-stack` service in `docker-compose.yaml` to build image locally using `Containerfile` instead of pulling pre-built image.

Sequence Diagram(s)

sequenceDiagram
    participant Client
    participant MetricsEndpoint
    participant SetupModelMetrics
    participant PrometheusExporter

    Client->>MetricsEndpoint: HTTP GET /metrics
    MetricsEndpoint->>SetupModelMetrics: await setup_model_metrics()
    SetupModelMetrics-->>MetricsEndpoint: (runs once, subsequent calls await same task)
    MetricsEndpoint->>PrometheusExporter: generate_latest(metrics_registry)
    PrometheusExporter-->>MetricsEndpoint: metrics data
    MetricsEndpoint->>Client: PlainTextResponse(metrics)

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

LCORE-220: Add metrics to lightspeed-stack #256: The main PR modifies the existing /metrics endpoint handler to be asynchronous and adds an awaited call to setup_model_metrics(), while the retrieved PR originally introduced the /metrics endpoint handler synchronously and added the setup_model_metrics() function and related metrics; thus, the main PR builds directly on and changes the same endpoint handler and setup function introduced in the retrieved PR.

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tisnik

Poem

A hop to async, metrics anew,
One setup runs, then hops are few.
Decorators guard with gentle might,
Logs now twinkle in the night.
Tests await, the code is neat—
Bunny’s metrics can’t be beat! 🐇✨

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umago · 2025-07-31T15:34:44Z

The E2E test is not using the proposed changes. This PR deletes the setup_model_metrics() from main.py:startup_event() but looking at the logs for the E2E test, it still failing on that point. It seems like it's checking out from some already committed changes, I think we need to rework how we setup the E2E test.

tisnik · 2025-08-01T07:35:26Z

/retest

umago · 2025-08-01T07:48:31Z

@tisnik the E2E test is not using the code from PR, we need to fix that first:

lightspeed-stack  |   File "/app-root/src/app/main.py", line 85, in startup_event
lightspeed-stack  |     await setup_model_metrics()
lightspeed-stack  |   File "/app-root/src/metrics/utils.py", line 17, in setup_model_metrics

umago · 2025-08-01T08:14:56Z

Rebased it on top of main, let's see

This patch moves the setup_model_metrics() from the service startup to the first time the /metrics endpoint is called. This speed up the lightspeed-stack service initialization and also make lightspeed-stack more resilient regarding service initialization order because it no longer requires llama-stack to be started first (as setup_model_metrics() tries to connect to llama-stack and fetch the list of models from it). Signed-off-by: Lucas Alvares Gomes <[email protected]> build actual image instead of using the actual one fix tests

tisnik

LGTM

umago force-pushed the setup-metrics branch from ed3b4da to b722fb4 Compare July 31, 2025 15:27

umago force-pushed the setup-metrics branch from b722fb4 to 8d190e4 Compare August 1, 2025 08:14

umago force-pushed the setup-metrics branch 2 times, most recently from 8d190e4 to 576341d Compare August 1, 2025 13:35

radofuchs force-pushed the setup-metrics branch from c8a8cb7 to 1acf3da Compare August 4, 2025 09:29

use fixed llama-stack version

19bf660

tisnik approved these changes Aug 5, 2025

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tisnik merged commit a3b530d into lightspeed-core:main Aug 5, 2025
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Delay setup_model_metrics() until /metrics is called #327

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