Add cost as tie breaker

wallyworld · wallyworld · commit b3eee975ee61 · 2014-02-14T09:54:46.000+10:00
diff --git a/environs/instances/instancetype.go b/environs/instances/instancetype.go
@@ -177,5 +177,11 @@ type byMemory []InstanceType
 func (s byMemory) Len() int      { return len(s) }
 func (s byMemory) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
 func (s byMemory) Less(i, j int) bool {
-	return s[i].Mem < s[j].Mem
+	inst0, inst1 := &s[i], &s[j]
+	if inst0.Mem != inst1.Mem {
+		return s[i].Mem < s[j].Mem
+	}
+	// Memory is equal, so use cost as a tie breaker.
+	// Result is in descending order of cost so instance with lowest cost is used.
+	return inst0.Cost > inst1.Cost
 }
diff --git a/environs/instances/instancetype_test.go b/environs/instances/instancetype_test.go
@@ -182,6 +182,17 @@ var getInstanceTypesTest = []struct {
 		},
 		expectedItypes: []string{"it-1"},
 	},
+	{
+		about: "largest mem available matching other constraints if mem not specified, cost is tie breaker",
+		cons:  "cpu-cores=4",
+		itypesToUse: []InstanceType{
+			{Id: "4", Name: "it-4", Arches: []string{"amd64"}, Mem: 1024, CpuCores: 2},
+			{Id: "3", Name: "it-3", Arches: []string{"amd64"}, Mem: 256, CpuCores: 4},
+			{Id: "2", Name: "it-2", Arches: []string{"amd64"}, Mem: 512, CpuCores: 4, Cost: 50},
+			{Id: "1", Name: "it-1", Arches: []string{"amd64"}, Mem: 512, CpuCores: 4, Cost: 100},
+		},
+		expectedItypes: []string{"it-2"},
+	},
 }
 
 func constraint(region, cons string) *InstanceConstraint {
