minor naming changes

Author: HaoyL666

cloud/scope/machine.go

@@ -237,9 +237,8 @@ func (m *MachineScope) GetOrCreateMachine(ctx context.Context) (*core.Instance,
 		}
 		// the random number generated is between zero and two, whereas we need a number between one and three
 		failureDomain = common.String(strconv.Itoa(int(randomFailureDomain.Int64()) + 1))
-		fd := m.OCIClusterAccessor.GetFailureDomains()[*failureDomain]
-		availabilityDomain = fd.Attributes[AvailabilityDomain]
-		faultDomain = fd.Attributes[FaultDomain]
+		availabilityDomain = m.OCIClusterAccessor.GetFailureDomains()[*failureDomain].Attributes[AvailabilityDomain]
+		faultDomain = m.OCIClusterAccessor.GetFailureDomains()[*failureDomain].Attributes[FaultDomain]
 	}
 
 	metadata := m.OCIMachine.Spec.Metadata
@@ -295,8 +294,8 @@ func (m *MachineScope) GetOrCreateMachine(ctx context.Context) (*core.Instance,
 	launchDetails.PreemptibleInstanceConfig = m.getPreemptibleInstanceConfig()
 	launchDetails.PlatformConfig = m.getPlatformConfig()
 	launchDetails.LaunchVolumeAttachments = m.getLaunchVolumeAttachments()
-	attempts := m.buildFaultDomainLaunchAttempts(availabilityDomain, faultDomain)
-	return m.launchInstanceWithFaultDomainRetry(ctx, launchDetails, attempts)
+	faultDomains := m.buildFaultDomainLaunchAttempts(availabilityDomain, faultDomain)
+	return m.launchInstanceWithFaultDomainRetry(ctx, launchDetails, faultDomains)
 }
 
 func (m *MachineScope) launchInstanceWithFaultDomainRetry(ctx context.Context, baseDetails core.LaunchInstanceDetails, attempts []faultDomainAttempt) (*core.Instance, error) {
@@ -336,18 +335,20 @@ func (m *MachineScope) launchInstanceWithFaultDomainRetry(ctx context.Context, b
 	return nil, lastErr
 }
 
+const defaultFaultDomainKey = "__no_fault_domain__"
+
 func (m *MachineScope) buildFaultDomainLaunchAttempts(availabilityDomain, initialFaultDomain string) []faultDomainAttempt {
-	attempts := []faultDomainAttempt{}
-	seen := map[string]struct{}{}
+	var attempts []faultDomainAttempt
+	seen := make(map[string]bool)
 	addAttempt := func(fd string) {
 		key := fd
 		if fd == "" {
-			key = "__default__"
+			key = defaultFaultDomainKey
 		}
-		if _, exists := seen[key]; exists {
+		if seen[key] {
 			return
 		}
-		seen[key] = struct{}{}
+		seen[key] = true
 		attempts = append(attempts, faultDomainAttempt{
 			AvailabilityDomain: availabilityDomain,
 			FaultDomain:        fd,