RabbitMQ一个简单可靠的方案(.Net Core实现)
前言
最近需要使用到消息队列相关技术,于是重新接触RabbitMQ。其中遇到了不少可靠性方面的问题,归纳了一下,大概有以下几种:
1. 临时异常,如数据库网络闪断、http请求临时失效等;
2. 时序异常,如A任务依赖于B任务,但可能由于调度或消费者分配的原因,导致A任务先于B任务执行;
3. 业务异常,由于系统测试不充分,上线后发现某几个或某几种消息无法正常处理;
4. 系统异常,业务中间件无法正常操作,如网络中断、数据库宕机等;
5. 非法异常,一些伪造、攻击类型的消息。
针对这些异常,我采用了一种基于消息审计、消息重试、消息检索、消息重发的方案。
方案
1. 消息均使用Exchange进行通讯,方式可以是direct或topic,不建议fanout。
2. 根据业务在Exchange下分配一个或多个Queue,同时设置一个审计线程(Audit)监听所有Queue,用于记录消息到MongoDB,同时又不阻塞正常业务处理。
3. 生产者(Publisher)在发布消息时,基于AMQP协议,生成消息标识MessageId和时间戳Timestamp,根据消息业务添加头信息Headers便于跟踪。
4. 消费者(Comsumer)消息处理失败时,则把消息发送到重试交换机(Retry Exchange),并设置过期(重试)时间及更新重试次数;如果超过重试次数则删除消息。
5. 重试交换机Exchange设置死信交换机(Dead Letter Exchange),消息过期后自动转发到业务交换机(Exchange)。
6. WebApi可以根据消息标识MessageId、时间戳Timestamp以及头信息Headers在MongoDB中对消息进行检索或重试。
注:选择MongoDB作为存储介质的主要原因是其对头信息(headers)的动态查询支持较好,同等的替代产品还可以是Elastic Search这些。
生产者(Publisher)
1. 设置断线自动恢复
var factory = new ConnectionFactory { Uri = new Uri("amqp://guest:guest@192.168.132.137:5672"), AutomaticRecoveryEnabled = true };
2. 定义Exchange,模式为direct
channel.ExchangeDeclare("Exchange", "direct");
3. 根据业务定义QueueA和QueueB
channel.QueueDeclare("QueueA", true, false, false); channel.QueueBind("QueueA", "Exchange", "RouteA"); channel.QueueDeclare("QueueB", true, false, false); channel.QueueBind("QueueB", "Exchange", "RouteB");
4. 启动消息发送确认机制,即需要收到RabbitMQ服务端的确认消息
channel.ConfirmSelect();
5. 设置消息持久化
var properties = channel.CreateBasicProperties(); properties.Persistent = true;
6. 生成消息标识MessageId、时间戳Timestamp以及头信息Headers
properties.MessageId = Guid.NewGuid().ToString("N"); properties.Timestamp = new AmqpTimestamp(DateTimeOffset.UtcNow.ToUnixTimeMilliseconds()); properties.Headers = new Dictionary<string, object> { { "key", "value" + i} };
7. 发送消息,偶数序列发送到QueueA(RouteA),奇数序列发送到QueueB(RouteB)
channel.BasicPublish("Exchange", i % 2 == 0 ? "RouteA" : "RouteB", properties, body);
8. 确定收到RabbitMQ服务端的确认消息
var isOk = channel.WaitForConfirms(); if (!isOk) { throw new Exception("The message is not reached to the server!"); }
完整代码
var factory = new ConnectionFactory { Uri = new Uri("amqp://guest:guest@localhost:5672"), AutomaticRecoveryEnabled = true }; using (var connection = factory.CreateConnection()) { using (var channel = connection.CreateModel()) { channel.ExchangeDeclare("Exchange", "direct"); channel.QueueDeclare("QueueA", true, false, false); channel.QueueBind("QueueA", "Exchange", "RouteA"); channel.QueueDeclare("QueueB", true, false, false); channel.QueueBind("QueueB", "Exchange", "RouteB"); channel.ConfirmSelect(); for (var i = 0; i < 2; i++) { var properties = channel.CreateBasicProperties(); properties.Persistent = true; properties.MessageId = Guid.NewGuid().ToString("N"); properties.Timestamp = new AmqpTimestamp(DateTimeOffset.UtcNow.ToUnixTimeMilliseconds()); properties.Headers = new Dictionary<string, object> { { "key", "value" + i} }; var message = "Hello " + i; var body = Encoding.UTF8.GetBytes(message); channel.BasicPublish("Exchange", i % 2 == 0 ? "RouteA" : "RouteB", properties, body); var isOk = channel.WaitForConfirms(); if (!isOk) { throw new Exception("The message is not reached to the server!"); } } } }
View Code
效果:QueueA和QueueB各一条消息,QueueAudit两条消息
注:Exchange下必须先声明Queue才能接收到消息,上述代码并没有QueueAudit的声明;需要手动声明,或者先执行下面的消费者程序进行声明。
正常消费者(ComsumerA)
1. 设置预取消息,避免公平轮训问题,可以根据需要设置预取消息数,这里是1
_channel.BasicQos(0, 1, false);
2. 声明Exchange和Queue
_channel.ExchangeDeclare("Exchange", "direct"); _channel.QueueDeclare("QueueA", true, false, false); _channel.QueueBind("QueueA", "Exchange", "RouteA");
3. 编写回调函数
var consumer = new EventingBasicConsumer(_channel); consumer.Received += (model, ea) => { //The QueueA is always successful. try { _channel.BasicAck(ea.DeliveryTag, false); } catch (AlreadyClosedException ex) { _logger.LogCritical(ex, "RabbitMQ is closed!"); } }; _channel.BasicConsume("QueueA", false, consumer);
注:设置了RabbitMQ的断线恢复机制,当RabbitMQ连接不可用时,与MQ通讯的操作会抛出AlreadyClosedException的异常,导致主线程退出,哪怕连接恢复了,程序也无法恢复,因此,需要捕获处理该异常。
异常消费者(ComsumerB)
1. 设置预取消息
_channel.BasicQos(0, 1, false);
2. 声明Exchange和Queue
_channel.ExchangeDeclare("Exchange", "direct");
_channel.QueueDeclare("QueueB", true, false, false);
_channel.QueueBind("QueueB", "Exchange", "RouteB");
3. 设置死信交换机(Dead Letter Exchange)
var retryDic = new Dictionary<string, object> { {"x-dead-letter-exchange", "Exchange"}, {"x-dead-letter-routing-key", "RouteB"} }; _channel.ExchangeDeclare("Exchange_Retry", "direct"); _channel.QueueDeclare("QueueB_Retry", true, false, false, retryDic); _channel.QueueBind("QueueB_Retry", "Exchange_Retry", "RouteB_Retry");
4. 重试设置,3次重试;第一次1秒,第二次10秒,第三次30秒
_retryTime = new List<int> { 1 * 1000, 10 * 1000, 30 * 1000 };
5. 获取当前重试次数
var retryCount = 0; if (ea.BasicProperties.Headers != null && ea.BasicProperties.Headers.ContainsKey("retryCount")) { retryCount = (int)ea.BasicProperties.Headers["retryCount"]; _logger.LogWarning($"[{DateTime.Now:yyyy-MM-dd HH:mm:ss}]Message:{ea.BasicProperties.MessageId}, {++retryCount} retry started..."); }
6. 发生异常,判断是否可以重试
private bool CanRetry(int retryCount) { return retryCount <= _retryTime.Count - 1; }
7. 可以重试,则启动重试机制
private void SetupRetry(int retryCount, string retryExchange, string retryRoute, BasicDeliverEventArgs ea) { var body = ea.Body; var properties = ea.BasicProperties; properties.Headers = properties.Headers ?? new Dictionary<string, object>(); properties.Headers["retryCount"] = retryCount; properties.Expiration = _retryTime[retryCount].ToString(); try { _channel.BasicPublish(retryExchange, retryRoute, properties, body); } catch (AlreadyClosedException ex) { _logger.LogCritical(ex, "RabbitMQ is closed!"); } }
完整代码
_channel.BasicQos(0, 1, false); _channel.ExchangeDeclare("Exchange", "direct"); _channel.QueueDeclare("QueueB", true, false, false); _channel.QueueBind("QueueB", "Exchange", "RouteB"); var retryDic = new Dictionary<string, object> { {"x-dead-letter-exchange", "Exchange"}, {"x-dead-letter-routing-key", "RouteB"} }; _channel.ExchangeDeclare("Exchange_Retry", "direct"); _channel.QueueDeclare("QueueB_Retry", true, false, false, retryDic); _channel.QueueBind("QueueB_Retry", "Exchange_Retry", "RouteB_Retry"); var consumer = new EventingBasicConsumer(_channel); consumer.Received += (model, ea) => { //The QueueB is always failed. bool canAck; var retryCount = 0; if (ea.BasicProperties.Headers != null && ea.BasicProperties.Headers.ContainsKey("retryCount")) { retryCount = (int)ea.BasicProperties.Headers["retryCount"]; _logger.LogWarning($"[{DateTime.Now:yyyy-MM-dd HH:mm:ss}]Message:{ea.BasicProperties.MessageId}, {++retryCount} retry started..."); } try { Handle(); canAck = true; } catch (Exception ex) { _logger.LogCritical(ex, "Error!"); if (CanRetry(retryCount)) { SetupRetry(retryCount, "Exchange_Retry", "RouteB_Retry", ea); canAck = true; } else { canAck = false; } } try { if (canAck) { _channel.BasicAck(ea.DeliveryTag, false); } else { _channel.BasicNack(ea.DeliveryTag, false, false); } } catch (AlreadyClosedException ex) { _logger.LogCritical(ex, "RabbitMQ is closed!"); } }; _channel.BasicConsume("QueueB", false, consumer);
View Code
审计消费者(Audit Comsumer)
1. 声明Exchange和Queue
_channel.ExchangeDeclare("Exchange", "direct"); _channel.QueueDeclare("QueueAudit", true, false, false); _channel.QueueBind("QueueAudit", "Exchange", "RouteA"); _channel.QueueBind("QueueAudit", "Exchange", "RouteB");
2. 排除死信Exchange转发过来的重复消息
if (ea.BasicProperties.Headers == null || !ea.BasicProperties.Headers.ContainsKey("x-death")) { ... }
3. 生成消息实体
var message = new Message { MessageId = ea.BasicProperties.MessageId, Body = ea.Body, Exchange = ea.Exchange, Route = ea.RoutingKey };
4. RabbitMQ会用bytes来存储字符串,因此,要把头中bytes转回字符串
if (ea.BasicProperties.Headers != null) { var headers = new Dictionary<string, object>(); foreach (var header in ea.BasicProperties.Headers) { if (header.Value is byte[] bytes) { headers[header.Key] = Encoding.UTF8.GetString(bytes); } else { headers[header.Key] = header.Value; } } message.Headers = headers; }
5. 把Unix格式的Timestamp转成UTC时间
if (ea.BasicProperties.Timestamp.UnixTime > 0) { message.TimestampUnix = ea.BasicProperties.Timestamp.UnixTime; var offset = DateTimeOffset.FromUnixTimeMilliseconds(ea.BasicProperties.Timestamp.UnixTime); message.Timestamp = offset.UtcDateTime; }
6. 消息存入MongoDB
_mongoDbContext.Collection<Message>().InsertOne(message, cancellationToken: cancellationToken);
MongoDB记录:
重试记录:
消息检索及重发(WebApi)
1. 通过消息Id检索消息
2. 通过头消息检索消息
3. 消息重发,会重新生成MessageId
Ack,Nack,Reject的关系
1. 消息处理成功,执行Ack,RabbitMQ会把消息从队列中删除。
2. 消息处理失败,执行Nack或者Reject:
a) 当requeue=true时,消息会重新回到队列,然后当前消费者会马上再取回这条消息;
b) 当requeue=false时,如果Exchange有设置Dead Letter Exchange,则消息会去到Dead Letter Exchange;
c) 当requeue=false时,如果Exchange没设置Dead Letter Exchange,则消息从队列中删除,效果与Ack相同。
3. Nack与Reject的区别在于:Nack可以批量操作,Reject只能单条操作。
RabbitMQ自动恢复
连接(Connection)恢复
1. 重连(Reconnect)
2. 恢复连接监听(Listeners)
3. 重新打开通道(Channels)
4. 恢复通道监听(Listeners)
5. 恢复basic.qos,publisher confirms以及transaction设置
拓扑(Topology)恢复
1. 重新声明交换机(Exchanges)
2. 重新声明队列(Queues)
3. 恢复所有绑定(Bindings)
4. 恢复所有消费者(Consumers)
异常处理机制
1. 临时异常,如数据库网络闪断、http请求临时失效等
通过短时间重试(如1秒后)的方式处理,也可以考虑Nack/Reject来实现重试(时效性更高)。
2. 时序异常,如A任务依赖于B任务,但可能由于调度或消费者分配的原因,导致A任务先于B任务执行
通过长时间重试(如1分钟、30分钟、1小时、1天等),等待B任务先执行完的方式处理。
3. 业务异常,由于系统测试不充分,上线后发现某几个或某几种消息无法正常处理
等系统修正后,通过消息重发的方式处理。
4. 系统异常,业务中间件无法正常操作,如网络中断、数据库宕机等
等系统恢复后,通过消息重发的方式处理。
5. 非法异常,一些伪造、攻击类型的消息
多次重试失败后,消息从队列中被删除,也可以针对此业务做进一步处理。