Fix bug in tie strategy prioritization

- It now will adjust prioritized list (of azs) each time it matches one
- This ensures that the prioritization will only happen dependent on the
number of existing instance azs at the time the TieStrategy was created.

[#137919209](https://www.pivotaltracker.com/story/show/137919209)

Signed-off-by: Difan Zhao <[email protected]>

src/bosh-director/lib/bosh/director/deployment_plan/placement_planner/tie_strategy.rb

@@ -10,7 +10,8 @@ def initialize(preferred_az_names)
 
             def call(azs)
               azs.find { |az|
-                @preferred_az_names.any? {|i| i == az.name }
+                i = @preferred_az_names.find_index {|az_name| az_name == az.name }
+                @preferred_az_names.delete_at(i) if i
               } || azs.min
             end
           end
@@ -23,7 +24,8 @@ def initialize(preferred_az_names, random: Random)
 
             def call(azs)
               azs.find { |az|
-                @preferred_az_names.any? {|i| i == az.name }
+                i = @preferred_az_names.find_index {|az_name| az_name == az.name }
+                @preferred_az_names.delete_at(i) if i
               } || azs.sample(random: @random)
             end
           end

src/bosh-director/lib/bosh/director/deployment_plan/placement_planner/unplaced_existing_instances.rb

@@ -40,7 +40,7 @@ def unclaimed
           end
 
           def azs
-            @az_name_to_existing_instances.keys
+            @instances.map(&:availability_zone)
           end
 
           private

src/bosh-director/spec/unit/deployment_plan/placement_planner/unplaced_existing_instances_spec.rb

@@ -3,15 +3,16 @@
 
 module Bosh::Director::DeploymentPlan
   describe PlacementPlanner::UnplacedExistingInstances do
-    subject { PlacementPlanner::UnplacedExistingInstances.new([instance1, instance2, instance3]) }
+    subject { PlacementPlanner::UnplacedExistingInstances.new([instance1, instance2, instance3, instance4]) }
 
     let(:instance1) { Bosh::Director::Models::Instance.make(availability_zone: '1') }
     let(:instance2) { Bosh::Director::Models::Instance.make(availability_zone: '2') }
     let(:instance3) { Bosh::Director::Models::Instance.make(availability_zone: '3') }
+    let(:instance4) { Bosh::Director::Models::Instance.make(availability_zone: '2') }
 
     describe 'azs' do
-      it 'should return a list of azs' do
-        expect(subject.azs).to eq(%w(1 2 3))
+      it 'should return an un-de-duped list of azs' do
+        expect(subject.azs).to eq(%w(1 2 3 2))
       end
     end
   end

src/bosh-director/spec/unit/deployment_plan/tie_strategy_spec.rb

@@ -8,7 +8,7 @@ module PlacementPlanner
       let(:az3) { AvailabilityZone.new("3", {}) }
 
       describe TieStrategy::MinWins do
-        subject { described_class.new(%w(3)) }
+        subject { described_class.new(%w(3 3)) }
 
         it 'chooses the minimum' do
           expect(subject.call([az1, az2])).to eq(az1)
@@ -17,10 +17,16 @@ module PlacementPlanner
         it 'prioritizes the priority' do
           expect(subject.call([az2, az3])).to eq(az3)
         end
+
+        it 'deletes an item from priority when we match based on priority' do
+          expect(subject.call([az1, az2, az3])).to eq(az3)
+          expect(subject.call([az1, az2, az3])).to eq(az3)
+          expect(subject.call([az1, az2, az3])).to eq(az1)
+        end
       end
 
       describe TieStrategy::RandomWins do
-        subject { described_class.new(%w(3), random: fake_random) }
+        subject { described_class.new(%w(3 3), random: fake_random) }
 
         let(:fake_random) do
           r = Object.new
@@ -35,7 +41,13 @@ def r.rand(n)
         end
 
         it 'prioritizes the priority' do
-          expect(subject.call([az2, az3])).to eq(az3)
+          expect(subject.call([az1, az2, az3])).to eq(az3)
+        end
+
+        it 'deletes an item from priority when we match based on priority' do
+          expect(subject.call([az1, az2, az3])).to eq(az3)
+          expect(subject.call([az1, az2, az3])).to eq(az3)
+          expect(subject.call([az1, az2, az3])).to eq(az2)
         end
       end
     end