fix: Enforce min_endpoint flag in Planner (#6637)

components/src/dynamo/planner/utils/agg_planner.py

@@ -210,7 +210,7 @@ class AggPlanner:
             return "up"
 
         # Scale down: ALL workers below boundary
-        if num_workers > 1:
+        if num_workers > self.config.min_endpoint:
             sensitivity = self.config.load_scaling_down_sensitivity / 100.0
             boundary = target * (num_workers - 1) / num_workers * sensitivity
             if all(
@@ -253,7 +253,7 @@ class AggPlanner:
         # Scale down: ALL workers below boundary
         # TODO: should we strictly enforce all workers below boundary?
         # how about user-configurable percentage?
-        if num_workers > 1:
+        if num_workers > self.config.min_endpoint:
             sensitivity = self.config.load_scaling_down_sensitivity / 100.0
             boundary = x_sla * (num_workers - 1) / num_workers * sensitivity
             if all(

components/src/dynamo/planner/utils/decode_planner.py

@@ -69,6 +69,13 @@ class DecodePlanner(BasePlanner):
                 m.get("active_decode_blocks", 0.0) < boundary for m in recent.values()
             )
             if all_below:
+                if num_workers - 1 < self.config.min_endpoint:
+                    logger.info(
+                        f"Load-based decode: ALL workers below boundary ({boundary:.1f}), "
+                        f"but cannot scale down below min_endpoint ({self.config.min_endpoint}); "
+                        f"maintaining {num_workers} decode workers"
+                    )
+                    return num_workers
                 logger.info(
                     f"Load-based decode: ALL workers below boundary ({boundary:.1f}), "
                     f"scaling down to {num_workers - 1}"

components/src/dynamo/planner/utils/disagg_planner.py

@@ -226,6 +226,10 @@ class DisaggPlanner:
                 final_p = max(final_p, self.shared_state.throughput_lower_bound_p)
                 final_d = max(final_d, self.shared_state.throughput_lower_bound_d)
 
+            # Enforce minimum endpoints
+            final_p = max(final_p, self.config.min_endpoint)
+            final_d = max(final_d, self.config.min_endpoint)
+
             # Apply GPU budget
             final_p, final_d = _apply_global_gpu_budget(final_p, final_d, self.config)
 

components/src/dynamo/planner/utils/planner_core.py

@@ -746,7 +746,9 @@ class BasePlanner:
 
     def apply_component_budget(self, desired_replicas: int) -> int:
         return _apply_component_gpu_budget(
-            desired_replicas, self._engine_num_gpu(), self.config
+            max(desired_replicas, self.config.min_endpoint),
+            self._engine_num_gpu(),
+            self.config,
         )
 
     async def _apply_scaling(self, desired_replicas: int) -> None:

components/src/dynamo/planner/utils/prefill_planner.py

@@ -78,6 +78,13 @@ class PrefillPlanner(BasePlanner):
                 m.get("active_prefill_tokens", 0.0) < boundary for m in recent.values()
             )
             if all_below:
+                if num_workers - 1 < self.config.min_endpoint:
+                    logger.info(
+                        f"Load-based prefill: ALL workers below boundary ({boundary:.1f}), "
+                        f"but cannot scale down below min_endpoint ({self.config.min_endpoint}); "
+                        f"maintaining {num_workers} prefill workers"
+                    )
+                    return num_workers
                 logger.info(
                     f"Load-based prefill: ALL workers below boundary ({boundary:.1f}), "
                     f"scaling down to {num_workers - 1}"