add buildbot extension for autoscaling nix builders

buildbot-ext/buildbot_autoscale_ext/configurator.py

@@ -0,0 +1,66 @@
+from __future__ import annotations
+
+import logging
+from typing import Any
+
+from buildbot.configurators import ConfiguratorBase
+
+from .settings import AutoscaleSettings
+from .steps import CapacityGateStep, CapacityReleaseStep
+
+log = logging.getLogger(__name__)
+
+
+class AutoscaleConfigurator(ConfiguratorBase):
+    def __init__(self, settings: AutoscaleSettings) -> None:
+        super().__init__()
+        self.settings = settings
+
+    def configure(self, config_dict: dict[str, Any]) -> None:
+        builders = config_dict.get("builders", [])
+        patched: list[str] = []
+
+        for builder in builders:
+            name = getattr(builder, "name", "")
+            if not isinstance(name, str) or not name.endswith("/nix-build"):
+                continue
+
+            factory = getattr(builder, "factory", None)
+            steps = getattr(factory, "steps", None)
+            if factory is None or not isinstance(steps, list):
+                log.warning("Skipping builder with unrecognized factory shape: %s", name)
+                continue
+
+            gate = CapacityGateStep(
+                name="Ensure remote builder capacity",
+                daemon_socket=self.settings.daemon_socket,
+                system_property=self.settings.system_property,
+                default_system=self.settings.default_system,
+                reserve_timeout_seconds=self.settings.reserve_timeout_seconds,
+                poll_interval_seconds=self.settings.poll_interval_seconds,
+                retry_max_attempts=self.settings.retry_max_attempts,
+                retry_base_seconds=self.settings.retry_base_seconds,
+                retry_max_seconds=self.settings.retry_max_seconds,
+                haltOnFailure=True,
+                flunkOnFailure=True,
+                warnOnFailure=False,
+            )
+            steps.insert(0, gate)
+
+            if self.settings.release_on_finish:
+                steps.append(
+                    CapacityReleaseStep(
+                        name="Release autoscaler reservation",
+                        daemon_socket=self.settings.daemon_socket,
+                        retry_max_attempts=self.settings.retry_max_attempts,
+                        retry_base_seconds=self.settings.retry_base_seconds,
+                        retry_max_seconds=self.settings.retry_max_seconds,
+                        alwaysRun=True,
+                        flunkOnFailure=False,
+                        warnOnFailure=True,
+                    )
+                )
+
+            patched.append(name)
+
+        log.info("AutoscaleConfigurator patched builders: %s", patched)