rpc: fix scaling policy get index response when policy is found.

.changelog/11579.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+rpc: Fixed scaling policy get index response when the policy is found
+```

nomad/scaling_endpoint.go

@@ -120,18 +120,18 @@ func (p *Scaling) GetPolicy(args *structs.ScalingPolicySpecificRequest,
 
 			reply.Policy = p
 
-			// Use the last index that affected the policy table
-			index, err := state.Index("scaling_policy")
-			if err != nil {
-				return err
-			}
-
-			// Ensure we never set the index to zero, otherwise a blocking query cannot be used.
-			// We floor the index at one, since realistically the first write must have a higher index.
-			if index == 0 {
-				index = 1
+			// If the state lookup returned a policy object, use the modify
+			// index for the response. Otherwise, use the index table to supply
+			// this, ensuring a non-zero value.
+			if p != nil {
+				reply.Index = p.ModifyIndex
+			} else {
+				index, err := state.Index("scaling_policy")
+				if err != nil {
+					return err
+				}
+				reply.Index = helper.Uint64Max(1, index)
 			}
-			reply.Index = index
 			return nil
 		}}
 	return p.srv.blockingRPC(&opts)

nomad/scaling_endpoint_test.go

@@ -36,7 +36,11 @@ func TestScalingEndpoint_GetPolicy(t *testing.T) {
 	p2 := mock.ScalingPolicy()
 	s1.fsm.State().UpsertScalingPolicies(1000, []*structs.ScalingPolicy{p1, p2})
 
-	// Lookup the policy
+	// Add another policy at a higher index.
+	p3 := mock.ScalingPolicy()
+	require.NoError(s1.fsm.State().UpsertScalingPolicies(2000, []*structs.ScalingPolicy{p3}))
+
+	// Lookup the first policy and perform assertions.
 	get := &structs.ScalingPolicySpecificRequest{
 		ID: p1.ID,
 		QueryOptions: structs.QueryOptions{
@@ -54,7 +58,7 @@ func TestScalingEndpoint_GetPolicy(t *testing.T) {
 	resp = structs.SingleScalingPolicyResponse{}
 	err = msgpackrpc.CallWithCodec(codec, "Scaling.GetPolicy", get, &resp)
 	require.NoError(err)
-	require.EqualValues(1000, resp.Index)
+	require.EqualValues(2000, resp.Index)
 	require.Nil(resp.Policy)
 }