Add metrics-server healthcheck

[i386]

Summary

Adds a process-level HTTP healthcheck for metrics-server at GET /health, returning 200 OK with {"status":"ok"}. This gives deploy and orchestration tooling a simple URL to verify that the metrics-server HTTP listener is alive without touching run lifecycle or OTLP ingest APIs.

Changes

• Adds the health HTTP handler.
• Wires GET /health into the metrics-server Axum router.
• Adds a focused unit test for the handler.
• Documents the healthcheck URL in the metrics-server README.

Validation

• cargo fmt --all -- --check
• cargo check -p metrics-server
• cargo test -p metrics-server --lib
• cargo clippy -p metrics-server --all-targets -- -D warnings
• cargo build -p metrics-server
• Live smoke: GET http://127.0.0.1:18080/health returned {"status":"ok"}

Summary by CodeRabbit

• New Features

  • Added HTTP health-check endpoint (/health) that returns JSON status confirmation. Enables external monitoring systems and orchestration platforms to verify service availability and operational readiness.

• Documentation

  • Updated README documentation to describe the health-check endpoint, including sample curl command demonstrating usage.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds a GET /health endpoint to the metrics-server crate. A new health async handler in api.rs returns {"status":"ok"} as JSON. The route is registered on the Axum router in server.rs. A unit test verifies the handler returns HTTP 200, and the README is updated with the endpoint description and a curl example.

Changes

Health endpoint for metrics-server

Layer / File(s)	Summary
Health handler and route wiring crates/metrics-server/src/api.rs, crates/metrics-server/src/server.rs	Adds pub(crate) async fn health() -> Json<Value> returning {"status":"ok"}, imports it in server.rs, and registers GET /health on the Axum router in serve_http.
Unit test and README docs crates/metrics-server/src/lib.rs, crates/metrics-server/README.md	Adds health_endpoint_reports_ok tokio test asserting StatusCode::OK; updates test imports; adds /health bullet to the Responsibilities list and a sample curl invocation.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 28.57% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Add metrics-server healthcheck' accurately summarizes the main change: adding a health check endpoint to the metrics-server.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@crates/metrics-server/src/lib.rs`:
- Around line 141-145: The test function health_endpoint_reports_ok currently
only validates the HTTP status code but does not verify the response body
structure. Add an assertion to extract the response body and validate that it
contains the expected JSON payload with the status field set to "ok". This will
ensure the endpoint contract is fully tested and will catch any future changes
to the response body structure, not just the status code.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: aa0fd27c-321f-4d0f-af57-477a44960d03

📥 Commits

Reviewing files that changed from the base of the PR and between 9b961c0 and 891f629.

📒 Files selected for processing (4)

• crates/metrics-server/README.md
• crates/metrics-server/src/api.rs
• crates/metrics-server/src/lib.rs
• crates/metrics-server/src/server.rs

[coderabbitai]

⚠️ Potential issue | 🟡 Minor | ⚡ Quick win

Assert the health response body contract, not only status.

This test passes even if the payload stops returning {"status":"ok"}. Add a body assertion to lock the endpoint contract.

Suggested test hardening

     #[tokio::test]
     async fn health_endpoint_reports_ok() {
         let response = health().await.into_response();
         assert_eq!(response.status(), StatusCode::OK);
+        let body = axum::body::to_bytes(response.into_body(), usize::MAX)
+            .await
+            .unwrap();
+        assert_eq!(body.as_ref(), br#"{"status":"ok"}"#);
     }

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@crates/metrics-server/src/lib.rs` around lines 141 - 145, The test function
health_endpoint_reports_ok currently only validates the HTTP status code but
does not verify the response body structure. Add an assertion to extract the
response body and validate that it contains the expected JSON payload with the
status field set to "ok". This will ensure the endpoint contract is fully tested
and will catch any future changes to the response body structure, not just the
status code.