车联网架构设计(二)

在上一篇博客车联网架构设计(一)_消息平台的搭建-CSDN博客中，我介绍了车联网平台需要实现的一些功能，并介绍了如何用EMQX+HAPROXY来搭建一个MQTT消息平台。车联网平台的应用需要消费车辆发布的消息，同时也会下发消息给车辆，以实现车辆控制等功能。通常我们会在MQTT消息平台收到车辆消息后对消息进行缓存，以供上层应用使用。我们可以直接把消息保存到数据库，或者引入一个消息队列，这样可以方便对应用和车辆之间进行解耦合。

这里我将介绍一下如何引入一个Kafka消息队列，把车辆以及上层应用之间需要交互的消息缓存到这个消息队列之中。

在EMQX的企业版中，提供了丰富的数据桥接功能，可以支持把MQTT消息桥接到其他外部系统，例如Kafka或数据库中。但是在开源版，只提供了很有限的数据桥接，不支持Kafka。为此我们可以通过给EMQX开发Hook extension的方式，来加载我们的插件，实现把数据桥接到Kafak。

在EMQX官网的介绍中，Hook扩展是通过gRPC的方式来实现的，支持多种编程语言。如下图：

这里我以Python为例子，来定义一个扩展。

搭建Kafka

首先是在K8S上部署一个Kafka集群，这里我选择了Strimizi的Kafka operator来部署

先创建一个namespace

kubectl create namespace kafka

安装Operator, CRD以及定义RBAC等

kubectl create -f 'https://strimzi.io/install/latest?namespace=kafka' -n kafka

创建一个只包含一个节点的Kafka

kubectl apply -f https://strimzi.io/examples/latest/kafka/kafka-persistent-single.yaml -n kafka

打开两个终端，分别运行以下的订阅和发布的指令，测试Kafka是否正常工作

kubectl -n kafka run kafka-producer -ti --image=quay.io/strimzi/kafka:0.38.0-kafka-3.6.0 --rm=true --restart=Never -- bin/kafka-console-producer.sh --bootstrap-server my-cluster-kafka-bootstrap:9092 --topic my-topic
kubectl -n kafka run kafka-consumer -ti --image=quay.io/strimzi/kafka:0.38.0-kafka-3.6.0 --rm=true --restart=Never -- bin/kafka-console-consumer.sh --bootstrap-server my-cluster-kafka-bootstrap:9092 --topic my-topic --from-beginning

开发ExHook

首先是获取当前EMQX版本定义的gPRC proto。在EMQX服务器的/opt/emqx/lib/emqx_exhook-5.0.14/priv/protos/目录下面有一个exhook.proto文件。

运行以下命令来基于这个proto生成python文件

python -m grpc_tools.protoc -I./ --python_out=. --pyi_out=. --grpc_python
_out=. ./exhook.proto

运行之后，在当前目录下会新生成三个文件，exhook_pb2_grpc.py，exhook_pb2.py，exhook_pb2.pyi

新建一个exhook_server.py文件，继承exhook_pb2_grpc里面的HookProviderServicer，注册对应事件的处理方法，如以下代码：

from concurrent import futures
import logging
from multiprocessing.sharedctypes import Valueimport grpcimport exhook_pb2
import exhook_pb2_grpcimport pickle
from kafka import KafkaProducerclass HookProvider(exhook_pb2_grpc.HookProviderServicer):def __init__(self):self.producer = KafkaProducer(bootstrap_servers='my-cluster-kafka-bootstrap.kafka.svc.cluster.local:9092')def OnProviderLoaded(self, request, context):print("OnProviderLoaded:", request)'''specs = [exhook_pb2.HookSpec(name="client.connect"),exhook_pb2.HookSpec(name="client.connack"),exhook_pb2.HookSpec(name="client.connected"),exhook_pb2.HookSpec(name="client.disconnected"),exhook_pb2.HookSpec(name="client.authenticate"),exhook_pb2.HookSpec(name="client.authorize"),exhook_pb2.HookSpec(name="client.subscribe"),exhook_pb2.HookSpec(name="client.unsubscribe"),exhook_pb2.HookSpec(name="session.created"),exhook_pb2.HookSpec(name="session.subscribed"),exhook_pb2.HookSpec(name="session.unsubscribed"),exhook_pb2.HookSpec(name="session.resumed"),exhook_pb2.HookSpec(name="session.discarded"),exhook_pb2.HookSpec(name="session.takenover"),exhook_pb2.HookSpec(name="session.terminated"),exhook_pb2.HookSpec(name="message.publish"),exhook_pb2.HookSpec(name="message.delivered"),exhook_pb2.HookSpec(name="message.acked"),exhook_pb2.HookSpec(name="message.dropped")]'''specs = [exhook_pb2.HookSpec(name="message.publish")]return exhook_pb2.LoadedResponse(hooks=specs)def OnProviderUnloaded(self, request, context):print("OnProviderUnloaded:", request)return exhook_pb2.EmptySuccess()def OnClientConnect(self, request, context):print("OnClientConnect:", request)return exhook_pb2.EmptySuccess()def OnClientConnack(self, request, context):print("OnClientConnack:", request)return exhook_pb2.EmptySuccess()def OnClientConnected(self, request, context):print("OnClientConnected:", request)return exhook_pb2.EmptySuccess()def OnClientDisconnected(self, request, context):print("OnClientDisconnected:", request)return exhook_pb2.EmptySuccess()def OnClientAuthenticate(self, request, context):print("OnClientAuthenticate:", request)reply = exhook_pb2.ValuedResponse(type="STOP_AND_RETURN", bool_result=True)return replydef OnClientAuthorize(self, request, context):print("OnClientAuthorize:", request)reply = exhook_pb2.ValuedResponse(type="STOP_AND_RETURN", bool_result=True)return replydef OnClientSubscribe(self, request, context):print("OnClientSubscribe:", request)return exhook_pb2.EmptySuccess()def OnClientUnsubscribe(self, request, context):print("OnClientUnsubscribe:", request)return exhook_pb2.EmptySuccess()def OnSessionCreated(self, request, context):print("OnSessionCreated:", request)return exhook_pb2.EmptySuccess()def OnSessionSubscribed(self, request, context):print("OnSessionSubscribed:", request)return exhook_pb2.EmptySuccess()def OnSessionUnsubscribed(self, request, context):print("OnSessionUnsubscribed:", request)return exhook_pb2.EmptySuccess()def OnSessionResumed(self, request, context):print("OnSessionResumed:", request)return exhook_pb2.EmptySuccess()def OnSessionDiscarded(self, request, context):print("OnSessionDiscarded:", request)return exhook_pb2.EmptySuccess()def OnSessionTakenover(self, request, context):print("OnSessionTakenover:", request)return exhook_pb2.EmptySuccess()def OnSessionTerminated(self, request, context):print("OnSessionTerminated:", request)return exhook_pb2.EmptySuccess()def OnMessagePublish(self, request, context):self.producer.send('testtopic', pickle.dumps(nmsg))reply = exhook_pb2.ValuedResponse(type="STOP_AND_RETURN", message=nmsg)return reply## case2: stop publish the 't/d' messages#def OnMessagePublish(self, request, context):#    nmsg = request.message#    if nmsg.topic == 't/d':#        nmsg.payload = b""#        nmsg.headers['allow_publish'] = b"false"##    reply = exhook_pb2.ValuedResponse(type="STOP_AND_RETURN", message=nmsg)#    return replydef OnMessageDelivered(self, request, context):print("OnMessageDelivered:", request)return exhook_pb2.EmptySuccess()def OnMessageDropped(self, request, context):print("OnMessageDropped:", request)return exhook_pb2.EmptySuccess()def OnMessageAcked(self, request, context):print("OnMessageAcked:", request)return exhook_pb2.EmptySuccess()def serve():server = grpc.server(futures.ThreadPoolExecutor(max_workers=10))exhook_pb2_grpc.add_HookProviderServicer_to_server(HookProvider(), server)server.add_insecure_port('[::]:9000')server.start()print("Started gRPC server on [::]:9000")server.wait_for_termination()if __name__ == '__main__':logging.basicConfig()serve()

解释一下代码，在OnProvidedLoader里面是加载各种事件的钩子，这里只加载message.publish事件。在OnMessagePublish是对应事件的处理函数，这里把收到的MQTT消息通过Pickle进行序列化，发送到Kafka的对应topic

部署ExHook

写一个Dockerfile，把代码打包为一个镜像

FROM python:3.7-slim
WORKDIR /app
COPY requirements.txt ./
RUN pip install -r requirements.txt
COPY . .
CMD ["python", "./exhook_server.py"]

requirements.txt文件内容为

grpcio==1.59.3
grpcio-tools==1.59.3
kafka-python==2.0.2

运行以下命令来构建镜像

docker build --network=host -t emqx_plugin_test:v1.0 .

创建一个部署这个镜像的deployment和service，然后部署到K8S

apiVersion: apps/v1
kind: Deployment
metadata:name: emqx-hookserver-deploymentlabels:app: hookservernamespace: emqx
spec:replicas: 1selector:matchLabels:app: hookservertemplate:metadata:labels:app: hookserverspec:containers:- name: hookserverimage: emqx_plugin_test:v1.0imagePullPolicy: Neverresources:requests:memory: "250Mi"cpu: "100m"limits:memory: "250Mi"cpu: "100m"ports:- name: rpccontainerPort: 9000
---
apiVersion: v1
kind: Service
metadata:name: hookserver-servicenamespace: emqx
spec:selector:app: hookserverports:- name: rpcport: 9000

回到EMQX的控制面板Dashboard，在ExHook里面添加，url填入http://hookserver-service.emqx.svc.cluster.local:9000，然后选择启用即可，可以看到状态为连接成功，并且显示注册了1个钩子。

在minikube上部署，一开始是显示连接中，等了很久仍然无法连接成功，最后查了资料，原来是coredns的问题，运行以下命令重启即可：

kubectl -n kube-system rollout restart deployment coredns

之后打开订阅Kafka的testtopic，然后通过MQTT连接到EMQX发送消息，可以看到Kafka能成功收到EMQX转发的消息。