限速设计及实现(微服务架构)

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开过车或者坐过车的都对限速是深恶痛绝吧，不过为了大家安全，忍一忍吧。系统究竟是如何判断车主是否超速那，本文主要介绍这个系统到底是如何设计的。本文基于微服务进行设计。

关于微服务，在微服务初探（0）和微服务-node.js中对微服务有简单的介绍。通过这篇文章，可以进一步了解微服务。

注：本文内容参考《Dapr For .NET developer》，专有名词保留英文原文，不做翻译。

Dapr

The Distributed Application Runtime (Dapr) provides APIs that simplify microservice connectivity. Whether your communication pattern is service to service invocation or pub/sub messaging, Dapr helps you write resilient and secured microservices.

Building blocks抽象了分布式应用能力的实现，service只需要和Building blocks进行交互即可。
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Dapr的现在和安装可参考Install the Dapr CLI。

限速设计

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这里面fine是罚单，罚款的意思。

VehicleState包括了车牌号，进入限速区域(Cameral)时间，退出限速区域(Cameral)时间。

public record struct VehicleState
{
    public string LicenseNumber { get; init; }
    public DateTime EntryTimestamp { get; init; }
    public DateTime? ExitTimestamp { get; init; }

    public VehicleState(string licenseNumber, DateTime entryTimestamp, DateTime? exitTimestamp = null)
    {
        this.LicenseNumber = licenseNumber;
        this.EntryTimestamp = entryTimestamp;
        this.ExitTimestamp = exitTimestamp;
    }
}

据此就可以计算出平均时速，然后再与规定的时速进行比较，如果超过了，不好意思，您将收到一封邮件，也可以用短信等方式发送给车主。而车主的邮件信息通过VehicleRegistrationService来获取。

车辆信息的结构体定义如下：

public record struct VehicleInfo(string VehicleId, string Brand, string Model, string OwnerName, string OwnerEmail);

代码实现

windows平台下需要将start-maildev.ps1修改为，修改参考maildev/maildev。

docker run -d -p 4000:1080 -p 4025:1025 --name dtc-maildev maildev/maildev

-d: 后台运行容器，并返回容器ID；

(1) CameralSimulation.cs

模拟进入和退出代码：

// simulate entry
DateTime entryTimestamp = DateTime.Now;
var vehicleRegistered = new VehicleRegistered
{
    Lane = _camNumber,
    LicenseNumber = GenerateRandomLicenseNumber(),
    Timestamp = entryTimestamp
};
await _trafficControlService.SendVehicleEntryAsync(vehicleRegistered);
Console.WriteLine($"Simulated ENTRY of vehicle with license-number {vehicleRegistered.LicenseNumber} in lane {vehicleRegistered.Lane}");

// simulate exit
TimeSpan exitDelay = TimeSpan.FromSeconds(_rnd.Next(_minExitDelayInS, _maxExitDelayInS) + _rnd.NextDouble());
Task.Delay(exitDelay).Wait();
vehicleRegistered.Timestamp = DateTime.Now;
vehicleRegistered.Lane = _rnd.Next(1, 4);
await _trafficControlService.SendVehicleExitAsync(vehicleRegistered);
Console.WriteLine($"Simulated EXIT of vehicle with license-number {vehicleRegistered.LicenseNumber} in lane {vehicleRegistered.Lane}");

跟踪 _trafficControlService.SendVehicleEntryAsync

 public async Task SendVehicleEntryAsync(VehicleRegistered vehicleRegistered)
 {
     var eventJson = JsonSerializer.Serialize(vehicleRegistered);
     var message = new MqttApplicationMessageBuilder()
         .WithTopic("trafficcontrol/entrycam")
         .WithPayload(Encoding.UTF8.GetBytes(eventJson))
         .WithAtMostOnceQoS()
         .Build();
     await _client.PublishAsync(message, CancellationToken.None);
 }

使用Input Binding来发布消息。可追踪到消息的订阅者是trafficcontrolservice。
（2）TrafficController.cs

[HttpPost("entrycam")]
 public async Task VehicleEntryAsync(VehicleRegistered msg)
 {
     try
     {
         // log entry
         _logger.LogInformation($"ENTRY detected in lane {msg.Lane} at {msg.Timestamp.ToString("hh:mm:ss")} " +
             $"of vehicle with license-number {msg.LicenseNumber}.");

         // store vehicle state
         var vehicleState = new VehicleState(msg.LicenseNumber, msg.Timestamp, null);
         await _vehicleStateRepository.SaveVehicleStateAsync(vehicleState);

         return Ok();
     }
     catch (Exception ex)
     {
         _logger.LogError(ex, "Error occurred while processing ENTRY");
         return StatusCode(500);
     }
 }

跟踪_vehicleStateRepository.SaveVehicleStateAsync(vehicleState)

public async Task SaveVehicleStateAsync(VehicleState vehicleState)
{
    await _daprClient.SaveStateAsync(
        DAPR_STORE_NAME, vehicleState.LicenseNumber, vehicleState);
}

使用state management building block来保存VehicleState。

同理可知退出时会调用trafficcontrolservice的VehicleExitAsync：

 [HttpPost("exitcam")]
    public async Task VehicleExitAsync(VehicleRegistered msg, [FromServices] DaprClient daprClient)
    {
        try
        {
            // get vehicle state
            var state = await _vehicleStateRepository.GetVehicleStateAsync(msg.LicenseNumber);
            if (state == default(VehicleState))
            {
                return NotFound();
            }

            // log exit
            _logger.LogInformation($"EXIT detected in lane {msg.Lane} at {msg.Timestamp.ToString("hh:mm:ss")} " +
                $"of vehicle with license-number {msg.LicenseNumber}.");

            // update state
            var exitState = state.Value with { ExitTimestamp = msg.Timestamp };
            await _vehicleStateRepository.SaveVehicleStateAsync(exitState);

            // handle possible speeding violation
            int violation = _speedingViolationCalculator.DetermineSpeedingViolationInKmh(exitState.EntryTimestamp, exitState.ExitTimestamp.Value);
            if (violation > 0)
            {
                _logger.LogInformation($"Speeding violation detected ({violation} KMh) of vehicle" +
                    $"with license-number {state.Value.LicenseNumber}.");

                var speedingViolation = new SpeedingViolation
                {
                    VehicleId = msg.LicenseNumber,
                    RoadId = _roadId,
                    ViolationInKmh = violation,
                    Timestamp = msg.Timestamp
                };

                // publish speedingviolation (Dapr publish / subscribe)
                await daprClient.PublishEventAsync("pubsub", "speedingviolations", speedingViolation);
            }

            return Ok();
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error occurred while processing EXIT");
            return StatusCode(500);
        }
    }

如果存在超速的话会调用：

await daprClient.PublishEventAsync("pubsub", "speedingviolations", speedingViolation)

根据配置文件

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: pubsub
  namespace: dapr-trafficcontrol
spec:
  type: pubsub.rabbitmq
  version: v1
  metadata:
  - name: host
    value: "amqp://localhost:5672"
  - name: durable
    value: "false"
  - name: deletedWhenUnused
    value: "false"
  - name: autoAck
    value: "false"
  - name: reconnectWait
    value: "0"
  - name: concurrency
    value: parallel
scopes:
  - trafficcontrolservice
  - finecollectionservice

可追踪到消息的订阅者是finecollectionservice。
（3）FineCollectionService

    [Topic("pubsub", "speedingviolations")]
    [Route("collectfine")]
    [HttpPost()]
    public async Task CollectFine(SpeedingViolation speedingViolation, [FromServices] DaprClient daprClient)
    {
        decimal fine = _fineCalculator.CalculateFine(_fineCalculatorLicenseKey!, speedingViolation.ViolationInKmh);

        // get owner info (Dapr service invocation)
        var vehicleInfo = _vehicleRegistrationService.GetVehicleInfo(speedingViolation.VehicleId).Result;

        // log fine
        string fineString = fine == 0 ? "tbd by the prosecutor" : $"{fine} Euro";
        _logger.LogInformation($"Sent speeding ticket to {vehicleInfo.OwnerName}. " +
            $"Road: {speedingViolation.RoadId}, Licensenumber: {speedingViolation.VehicleId}, " +
            $"Vehicle: {vehicleInfo.Brand} {vehicleInfo.Model}, " +
            $"Violation: {speedingViolation.ViolationInKmh} Km/h, Fine: {fineString}, " +
            $"On: {speedingViolation.Timestamp.ToString("dd-MM-yyyy")} " +
            $"at {speedingViolation.Timestamp.ToString("hh:mm:ss")}.");

        // send fine by email (Dapr output binding)
        var body = EmailUtils.CreateEmailBody(speedingViolation, vehicleInfo, fineString);
        var metadata = new Dictionary
        {
            ["emailFrom"] = "[email protected]",
            ["emailTo"] = vehicleInfo.OwnerEmail,
            ["subject"] = $"Speeding violation on the {speedingViolation.RoadId}"
        };
        await daprClient.InvokeBindingAsync("sendmail", "create", body, metadata);

        return Ok();
    }

其中vehicleInfo 的值是通过service invocation调用VehicleRegistrationService获取的。

最后通过Output Binding来发送邮件:

await daprClient.InvokeBindingAsync("sendmail", "create", body, metadata);

运行

1. start-all.ps1
2. dapr run --app-id vehicleregistrationservice --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 --config ../dapr/config/config.yaml --components-path ../dapr/components dotnet run
3. dapr run --app-id finecollectionservice --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 --config ../dapr/config/config.yaml --components-path ../dapr/components dotnet run
4. dapr run --app-id trafficcontrolservice --app-port 6000 --dapr-http-port 3600 --dapr-grpc-port 60000 --config ../dapr/config/config.yaml --components-path ../dapr/components dotnet run
5. cd Simulation && dotnet run

最终结果：
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车辆的进入退出信息都会实时捕获到，如果有超速信息，会通过邮件发送。
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写在最后

可视化版本

cd .\VisualSimulation\ && dotnet run

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视频可参见： https://live.csdn.net/v/238245

rabbitmq管理界面

默认账号密码都是guest。
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