feat(BA-6242): give custom runtime variant a default health check

changes/11863.feature.md

@@ -0,0 +1 @@
+Apply a default health check (/health, 1800s initial delay) to the custom runtime variant so model deployments no longer fail health checks while large models load

fixtures/manager/example-runtime-variants.json

@@ -135,7 +135,19 @@
       "description": "Custom (Default)",
       "reads_vfolder_config_files": true,
       "default_model_definition": {
-        "models": null
+        "models": [
+          {
+            "name": "custom-model",
+            "service": {
+              "health_check": {
+                "path": "/health",
+                "interval": 10.0,
+                "max_retries": 10,
+                "initial_delay": 1800.0
+              }
+            }
+          }
+        ]
       }
     }
   ]

src/ai/backend/install/fixtures/example-runtime-variants.json

@@ -135,7 +135,19 @@
       "description": "Custom (Default)",
       "reads_vfolder_config_files": true,
       "default_model_definition": {
-        "models": null
+        "models": [
+          {
+            "name": "custom-model",
+            "service": {
+              "health_check": {
+                "path": "/health",
+                "interval": 10.0,
+                "max_retries": 10,
+                "initial_delay": 1800.0
+              }
+            }
+          }
+        ]
       }
     }
   ]

src/ai/backend/manager/models/alembic/versions/ed42bc179b91_set_custom_runtime_variant_default_definition.py

@@ -0,0 +1,79 @@
+"""seed custom runtime_variant default_model_definition
+
+The ``custom`` variant previously held an empty Draft ({"models": null}),
+so a deployment that omitted ``health_check`` in its model-definition.yaml
+fell back to the schema default ``initial_delay`` of 60s — too short for
+large models that take minutes to load, causing premature unhealthy
+routes. Seed a baseline ``health_check`` (path ``/health``,
+``initial_delay`` 1800s) matching the prebuilt variants. The user's
+model-definition.yaml / request still override it field-by-field, so this
+acts purely as a fallback layer. Operator-customised rows are left as-is.
+
+Revision ID: ed42bc179b91
+Revises: 0113c63f3261
+Create Date: 2026-05-29
+
+"""
+
+# Part of: 26.6.0
+
+import json
+from typing import Any
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "ed42bc179b91"
+down_revision = "0113c63f3261"
+branch_labels = None
+depends_on = None
+
+
+_CUSTOM_DEFINITION_WITH_HEALTH_CHECK: dict[str, Any] = {
+    "models": [
+        {
+            "name": "custom-model",
+            "service": {
+                "health_check": {
+                    "path": "/health",
+                    "interval": 10.0,
+                    "max_retries": 10,
+                    "initial_delay": 1800.0,
+                },
+            },
+        }
+    ]
+}
+
+_EMPTY_DEFINITION: dict[str, Any] = {"models": None}
+
+
+def upgrade() -> None:
+    # Seed only the rows still holding the original empty definition, so an
+    # operator-customised custom variant is left untouched.
+    op.execute(
+        sa.text(
+            "UPDATE runtime_variants "
+            "SET default_model_definition = CAST(:custom_definition_with_health_check AS JSONB) "
+            "WHERE name = 'custom' AND default_model_definition = CAST(:empty_definition AS JSONB)"
+        ).bindparams(
+            custom_definition_with_health_check=json.dumps(_CUSTOM_DEFINITION_WITH_HEALTH_CHECK),
+            empty_definition=json.dumps(_EMPTY_DEFINITION),
+        )
+    )
+
+
+def downgrade() -> None:
+    # Revert only the value this migration set; leave later operator edits intact.
+    op.execute(
+        sa.text(
+            "UPDATE runtime_variants "
+            "SET default_model_definition = CAST(:empty_definition AS JSONB) "
+            "WHERE name = 'custom' "
+            "AND default_model_definition = CAST(:custom_definition_with_health_check AS JSONB)"
+        ).bindparams(
+            custom_definition_with_health_check=json.dumps(_CUSTOM_DEFINITION_WITH_HEALTH_CHECK),
+            empty_definition=json.dumps(_EMPTY_DEFINITION),
+        )
+    )