fix: use lazy loading for DEFAULT_METRICS_LOG_PATH

Author: cbartz

github-runner-manager/src/github_runner_manager/metrics/events.py

@@ -13,8 +13,7 @@
 from github_runner_manager.errors import IssueMetricEventError
 from github_runner_manager.manager.vm_manager import CodeInformation
 
-METRICS_LOG_PATH = Path(os.getenv("METRICS_LOG_PATH", "/var/log/github-runner-metrics.log"))
-
+_DEFAULT_METRICS_LOG_PATH = "/var/log/github-runner-metrics.log"
 
 logger = logging.getLogger(__name__)
 
@@ -156,8 +155,14 @@ def issue_event(event: Event) -> None:
     Raises:
         IssueMetricEventError: If the event cannot be logged.
     """
+    metrics_log_path = _get_metrics_log_path()
     try:
-        with METRICS_LOG_PATH.open(mode="a", encoding="utf-8") as metrics_file:
+        with metrics_log_path.open(mode="a", encoding="utf-8") as metrics_file:
             metrics_file.write(f"{event.json(exclude_none=True)}\n")
     except OSError as exc:
-        raise IssueMetricEventError(f"Cannot write to {METRICS_LOG_PATH}") from exc
+        raise IssueMetricEventError(f"Cannot write to {metrics_log_path}") from exc
+
+
+def _get_metrics_log_path() -> Path:
+    """Get the metrics log path, reading the env var at call time rather than import time."""
+    return Path(os.getenv("METRICS_LOG_PATH", _DEFAULT_METRICS_LOG_PATH))

github-runner-manager/tests/unit/metrics/test_events.py

@@ -13,9 +13,7 @@
 @pytest.fixture(autouse=True, name="patch_metrics_path")
 def patch_metrics_path_fixture(monkeypatch: pytest.MonkeyPatch, tmp_path: Path):
     """Patch the hardcoded metrics log path."""
-    monkeypatch.setattr(
-        "github_runner_manager.metrics.events.METRICS_LOG_PATH", Path(tmp_path / "metrics.log")
-    )
+    monkeypatch.setenv("METRICS_LOG_PATH", str(tmp_path / "metrics.log"))
 
 
 def test_issue_events_logs_events(tmp_path: Path):
@@ -28,7 +26,7 @@ def test_issue_events_logs_events(tmp_path: Path):
 
     events.issue_event(event)
 
-    assert json.loads(events.METRICS_LOG_PATH.read_text()) == {
+    assert json.loads(events._get_metrics_log_path().read_text()) == {
         "event": "runner_installed",
         "timestamp": 123,
         "flavor": "small",
@@ -55,7 +53,7 @@ def test_issue_events_exclude_none_values(tmp_path: Path):
 
     events.issue_event(event)
 
-    assert json.loads(events.METRICS_LOG_PATH.read_text()) == {
+    assert json.loads(events._get_metrics_log_path().read_text()) == {
         "event": "runner_stop",
         "timestamp": 123,
         "flavor": "small",