1 files changed, 99 insertions, 0 deletions
diff --git a/src/pybind/mgr/mds_autoscaler/module.py b/src/pybind/mgr/mds_autoscaler/module.py
new file mode 100644
index 000000000..2f780059c
--- /dev/null
+++ b/src/pybind/mgr/mds_autoscaler/module.py
@@ -0,0 +1,99 @@
+"""
+Automatically scale MDSs based on status of the file-system using the FSMap
+"""
+
+import logging
+from typing import Any, Optional
+from mgr_module import MgrModule, NotifyType
+from orchestrator._interface import MDSSpec, ServiceSpec
+import orchestrator
+import copy
+
+log = logging.getLogger(__name__)
+
+
+class MDSAutoscaler(orchestrator.OrchestratorClientMixin, MgrModule):
+    """
+    MDS autoscaler.
+    """
+    NOTIFY_TYPES = [NotifyType.fs_map]
+
+    def __init__(self, *args: Any, **kwargs: Any) -> None:
+        MgrModule.__init__(self, *args, **kwargs)
+        self.set_mgr(self)
+
+    def get_service(self, fs_name: str) -> Optional[orchestrator.ServiceDescription]:
+        service = f"mds.{fs_name}"
+        completion = self.describe_service(service_type='mds',
+                                           service_name=service,
+                                           refresh=True)
+        orchestrator.raise_if_exception(completion)
+        if completion.result:
+            return completion.result[0]
+        return None
+
+    def update_daemon_count(self, spec: ServiceSpec, fs_name: str, abscount: int) -> MDSSpec:
+        ps = copy.deepcopy(spec.placement)
+        ps.count = abscount
+        newspec = MDSSpec(service_type=spec.service_type,
+                          service_id=spec.service_id,
+                          placement=ps)
+        return newspec
+
+    def get_required_standby_count(self, fs_map: dict, fs_name: str) -> int:
+        assert fs_map is not None
+        for fs in fs_map['filesystems']:
+            if fs['mdsmap']['fs_name'] == fs_name:
+                return fs['mdsmap']['standby_count_wanted']
+        assert False
+
+    def get_required_max_mds(self, fs_map: dict, fs_name: str) -> int:
+        assert fs_map is not None
+        for fs in fs_map['filesystems']:
+            if fs['mdsmap']['fs_name'] == fs_name:
+                return fs['mdsmap']['max_mds']
+        assert False
+
+    def verify_and_manage_mds_instance(self, fs_map: dict, fs_name: str) -> None:
+        assert fs_map is not None
+
+        try:
+            svc = self.get_service(fs_name)
+            if not svc:
+                self.log.info(f"fs {fs_name}: no service defined; skipping")
+                return
+            if not svc.spec.placement.count:
+                self.log.info(f"fs {fs_name}: service does not specify a count; skipping")
+                return
+
+            standbys_required = self.get_required_standby_count(fs_map, fs_name)
+            max_mds = self.get_required_max_mds(fs_map, fs_name)
+            want = max_mds + standbys_required
+
+            self.log.info(f"fs {fs_name}: "
+                          f"max_mds={max_mds} "
+                          f"standbys_required={standbys_required}, "
+                          f"count={svc.spec.placement.count}")
+
+            if want == svc.spec.placement.count:
+                return
+
+            self.log.info(f"fs {fs_name}: adjusting daemon count from {svc.spec.placement.count} to {want}")
+            newspec = self.update_daemon_count(svc.spec, fs_name, want)
+            completion = self.apply_mds(newspec)
+            orchestrator.raise_if_exception(completion)
+        except orchestrator.OrchestratorError as e:
+            self.log.exception(f"fs {fs_name}: exception while updating service: {e}")
+            pass
+
+    def notify(self, notify_type: NotifyType, notify_id: str) -> None:
+        if notify_type != NotifyType.fs_map:
+            return
+        fs_map = self.get('fs_map')
+        if not fs_map:
+            return
+
+        # we don't know for which fs config has been changed
+        for fs in fs_map['filesystems']:
+            fs_name = fs['mdsmap']['fs_name']
+            self.verify_and_manage_mds_instance(fs_map, fs_name)