deflake autoscaling basic with min aggregation

[abrarsheikh]

flaky test

RAY_SERVE_HANDLE_AUTOSCALING_METRIC_PUSH_INTERVAL_S=0.1 \                                                                                                                                                                                                                        RAY_SERVE_AGGREGATE_METRICS_AT_CONTROLLER=1 \
RAY_SERVE_COLLECT_AUTOSCALING_METRICS_ON_HANDLE=0 \
pytest -svvx "python/ray/serve/tests/test_autoscaling_policy.py::TestAutoscalingMetrics::test_basic[min]"

What I think is the likely cause

When using RAY_SERVE_AGGREGATE_METRICS_AT_CONTROLLER=1 with min aggregation:

1. Replicas emit metrics at slightly different times (even if just 10ms apart due to the timestamp bucketing/rounding)

2. The merged timeseries reflects the ramp-up:

   • At t=0: Maybe only replica 1 is reporting → total = 25 requests
   • At t=0.01: Replica 2 starts reporting → total = 40 requests
   • At t=0.02: Replica 3 starts reporting → total = 50 requests
   • etc.

3. min aggregation captures the starting point:

   • aggregate_timeseries(..., aggregation_function="min") takes the minimum value from the merged timeseries
   • This will always be one of those initial low values (like 25) when only a subset of replicas had started reporting
   • This value can never be ≥ 45, making the test inherently flaky

Removing min from test fixture.

I think a more robust solution is to keep the last report in the controller, generate the final time series using both reports, then clip the data and mid-point, then apply the aggregation function.

[gemini-code-assist]

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[akyang-anyscale]

what's the reasoning behind the flakiness?