From f61f8e4d790fabf7fbd87c2b938a93eb2340aff1 Mon Sep 17 00:00:00 2001
From: Sage Weil <sage@redhat.com>
Date: Sun, 8 Mar 2020 12:01:09 -0500
Subject: [PATCH] mgr/cephadm: allow count == 0

Scale a service down to 0 without removing the spec.

Signed-off-by: Sage Weil <sage@redhat.com>
---
 src/pybind/mgr/cephadm/module.py              |  5 +++++
 .../mgr/cephadm/tests/test_scheduling.py      | 20 +++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/src/pybind/mgr/cephadm/module.py b/src/pybind/mgr/cephadm/module.py
index dab91bed559..362dbeb8db1 100644
--- a/src/pybind/mgr/cephadm/module.py
+++ b/src/pybind/mgr/cephadm/module.py
@@ -2980,6 +2980,10 @@ class HostAssignment(object):
         """
         Load hosts into the spec.placement.hosts container.
         """
+        # count == 0
+        if self.spec.placement.count == 0:
+            return []
+
         # respect any explicit host list
         if self.spec.placement.hosts and not self.spec.placement.count:
             logger.debug('Provided hosts: %s' % self.spec.placement.hosts)
@@ -2994,6 +2998,7 @@ class HostAssignment(object):
             logger.debug('All hosts: {}'.format(candidates))
             return candidates
 
+
         count = 0
         if self.spec.placement.hosts and \
            self.spec.placement.count and \
diff --git a/src/pybind/mgr/cephadm/tests/test_scheduling.py b/src/pybind/mgr/cephadm/tests/test_scheduling.py
index 7c6132c098d..abd3b3e4e2d 100644
--- a/src/pybind/mgr/cephadm/tests/test_scheduling.py
+++ b/src/pybind/mgr/cephadm/tests/test_scheduling.py
@@ -22,6 +22,15 @@ class NodeAssignmentTest(NamedTuple):
             [],
             ['smithi060']
         ),
+        # zero count
+        NodeAssignmentTest(
+            'mon',
+            PlacementSpec(count=0),
+            ['smithi060'],
+            [],
+            []
+        ),
+
         # all_hosts
         NodeAssignmentTest(
             'mon',
@@ -44,6 +53,17 @@ class NodeAssignmentTest(NamedTuple):
             ],
             ['host1', 'host2', 'host3']
         ),
+        # zero count + partial host list
+        NodeAssignmentTest(
+            'mon',
+            PlacementSpec(count=0, hosts=['host3']),
+            'host1 host2 host3'.split(),
+            [
+                DaemonDescription('mon', 'a', 'host1'),
+                DaemonDescription('mon', 'b', 'host2'),
+            ],
+            []
+        ),
         # count + partial host list + existing
         NodeAssignmentTest(
             'mon',
-- 
2.39.5