refactor: split container switch and commit steps

internal/backendupdate/container.go

@@ -517,53 +517,15 @@ func (u *Updater) switchAndCommitContainer(ctx context.Context, transactionID st
 		}
 		switch record.State {
 		case transaction.StateSwitching:
-			reportProgress(report, Progress{TransactionID: transactionID, State: record.State, Message: fmt.Sprintf("Switching host Nginx backend traffic to port %d", request.TargetPort)})
+			if err := u.switchContainerTraffic(ctx, transactionID, request, before, after, report); err != nil {
-			operation := &gatewayOperation{controller: u.gateway, before: before, after: after, receiptPath: request.GatewayReceiptPath}
-			if _, err := u.coordinator.ExecuteStep(ctx, transactionID, containerGatewaySwitchIntent(request), operation); err != nil {
-				return u.rollbackContainer(ctx, transactionID, request, before, after, err)
-			}
-			if _, err := u.store.Transition(ctx, transactionID, transaction.StateVerifying, "host Nginx now routes backend traffic to the healthy container slot"); err != nil {
 				return err
 			}
 		case transaction.StateVerifying:
-			message := "container backend switch verified"
+			if err := u.markContainerDraining(ctx, transactionID, request); err != nil {
-			if request.PreviousContainer != "" {
-				message += "; previous container draining"
-			}
-			if _, err := u.store.Transition(ctx, transactionID, transaction.StateDraining, message); err != nil {
 				return err
 			}
 		case transaction.StateDraining:
-			if request.PreviousContainer != "" {
+			return u.drainAndCommitContainer(ctx, transactionID, request, report)
-				reportProgress(report, Progress{TransactionID: transactionID, State: record.State, Message: fmt.Sprintf("Draining previous backend container for %s", u.drain)})
-				if err := waitContext(ctx, u.drain); err != nil {
-					return err
-				}
-				operation := &containerStopOperation{engine: u.engine, name: request.PreviousContainer, stopGraceSeconds: u.containerStopGraceSeconds}
-				if _, err := u.coordinator.ExecuteStep(ctx, transactionID, stopPreviousContainerIntent(request), operation); err != nil {
-					return err
-				}
-			}
-			target, err := u.engine.InspectContainer(ctx, request.TargetContainer)
-			if err != nil {
-				return fmt.Errorf("inspect target backend container before commit: %w", err)
-			}
-			if !target.Running || target.Dead || target.ID == "" {
-				return fmt.Errorf("target backend container %s is not running with an exact identity", request.TargetContainer)
-			}
-			if target.ImageReference != request.ImmutableReference && target.ImageReference != request.ImageReference {
-				return fmt.Errorf("target backend container %s image reference does not match the transaction", request.TargetContainer)
-			}
-			_, err = u.store.CommitBackendContainerDeployment(ctx, transactionID, transaction.BackendContainerDeployment{
-				ActivePort:    request.TargetPort,
-				ContainerName: request.TargetContainer,
-				ImageDigest:   request.ImageDigest,
-				ContainerID:   target.ID,
-			}, "container backend update committed")
-			if err == nil {
-				reportProgress(report, Progress{TransactionID: transactionID, State: transaction.StateCommitted, Message: "Container backend update committed"})
-			}
-			return err
 		case transaction.StateCommitted:
 			return nil
 		case transaction.StateRollingBack:
@@ -574,6 +536,53 @@ func (u *Updater) switchAndCommitContainer(ctx context.Context, transactionID st
 	}
 }
 
+func (u *Updater) switchContainerTraffic(ctx context.Context, transactionID string, request persistedContainerRequest, before hostnginx.Snapshot, after hostnginx.Snapshot, report ProgressReporter) error {
+	reportProgress(report, Progress{TransactionID: transactionID, State: transaction.StateSwitching, Message: fmt.Sprintf("Switching host Nginx backend traffic to port %d", request.TargetPort)})
+	operation := &gatewayOperation{controller: u.gateway, before: before, after: after, receiptPath: request.GatewayReceiptPath}
+	if _, err := u.coordinator.ExecuteStep(ctx, transactionID, containerGatewaySwitchIntent(request), operation); err != nil {
+		return u.rollbackContainer(ctx, transactionID, request, before, after, err)
+	}
+	_, err := u.store.Transition(ctx, transactionID, transaction.StateVerifying, "host Nginx now routes backend traffic to the healthy container slot")
+	return err
+}
+
+func (u *Updater) markContainerDraining(ctx context.Context, transactionID string, request persistedContainerRequest) error {
+	message := "container backend switch verified"
+	if request.PreviousContainer != "" {
+		message += "; previous container draining"
+	}
+	_, err := u.store.Transition(ctx, transactionID, transaction.StateDraining, message)
+	return err
+}
+
+func (u *Updater) drainAndCommitContainer(ctx context.Context, transactionID string, request persistedContainerRequest, report ProgressReporter) error {
+	if request.PreviousContainer != "" {
+		reportProgress(report, Progress{TransactionID: transactionID, State: transaction.StateDraining, Message: fmt.Sprintf("Draining previous backend container for %s", u.drain)})
+		if err := waitContext(ctx, u.drain); err != nil {
+			return err
+		}
+		operation := &containerStopOperation{engine: u.engine, name: request.PreviousContainer, stopGraceSeconds: u.containerStopGraceSeconds}
+		if _, err := u.coordinator.ExecuteStep(ctx, transactionID, stopPreviousContainerIntent(request), operation); err != nil {
+			return err
+		}
+	}
+	target, err := u.engine.InspectContainer(ctx, request.TargetContainer)
+	if err != nil {
+		return fmt.Errorf("inspect target backend container before commit: %w", err)
+	}
+	if !target.Running || target.Dead || target.ID == "" {
+		return fmt.Errorf("target backend container %s is not running with an exact identity", request.TargetContainer)
+	}
+	if target.ImageReference != request.ImmutableReference && target.ImageReference != request.ImageReference {
+		return fmt.Errorf("target backend container %s image reference does not match the transaction", request.TargetContainer)
+	}
+	_, err = u.store.CommitBackendContainerDeployment(ctx, transactionID, transaction.BackendContainerDeployment{ActivePort: request.TargetPort, ContainerName: request.TargetContainer, ImageDigest: request.ImageDigest, ContainerID: target.ID}, "container backend update committed")
+	if err == nil {
+		reportProgress(report, Progress{TransactionID: transactionID, State: transaction.StateCommitted, Message: "Container backend update committed"})
+	}
+	return err
+}
+
 // rollbackContainer 执行容器后端补偿：恢复 Nginx 上游、停止被补偿的目标容器，并
 // 将事务迁入 RolledBack 状态。cause 为触发补偿的原始错误，会与补偿过程中的错误
 // 合并后返回。