Communication protocol and message format between microservices

The communication between services follows IPC（Inter-Process Communication, Interprocess communication ） standard . The way of communication between them , It can be analyzed according to the following dimensions .

First, it is divided according to synchronous and asynchronous methods . The synchronization mode is only one-to-one , Asynchronous mode has one to one and one to many .

It can also be divided from message format and communication protocol . Message formats are text-based and binary based . Communication protocols are synchronous and asynchronous . Synchronous communication protocols include HTTP REST and gRPC. Asynchronous communication protocols include AMQP or STMP.

The essence of interprocess communication is to exchange messages . Messages usually include data , Therefore, the choice of message format has a great relationship with the efficiency of data transmission between processes . Text based message format . The advantage is high readability , The disadvantage is that the message is lengthy , In especial XML. If in a scenario sensitive to efficiency and performance , You need to use binary messaging format . Binary based messaging format . If we need to consider avoiding API Problems caused by version changes , Try to use Protocol Buffer. In synchronous mode , Whether it's REST still gPRC, All need to follow the remote procedure call RPI Mechanism .

REST It's a use HTTP Interprocess communication mechanism of the protocol , Use HTTP Verb （ Such as GET、POST、PUT etc. ） Operating resources , Use URL Call these resources .

REST The advantages of ： It's easy to operate 、 You can use browser extensions postman Plug in or curl Command line to test HTTP API、 Direct support request / Responsive communication 、HTTP Firewall friendly 、 No intermediate agent is needed, which simplifies the system architecture .

REST The shortcomings of ： Only requests... Are supported / Responsive communication ; May result in reduced availability ; Because the client and server are REST API You must remain online during the call , No proxy buffered messages ; The client must know the location of the service instance （URL）; Clients must use service discovery opportunities to locate service instances ; Getting multiple resources in a single request is challenging ; It is difficult to map multiple update operations to HTTP Verb .

Precisely because REST In the way ,HTTP Provide only a limited number of verbs , Designed to support multiple update operations REST API Not easy , therefore gRPC emerge as the times require .gRPC Use Protocol Buffer Messaging format .

Asynchronous communication protocol between microservices . We deliver messages in message oriented middleware , Use XML or JSON A text message . In a distributed system , The most common way of asynchronous communication between services is to send messages . We call the tool responsible for transforming the sender's formal messaging protocol into the receiver's formal messaging protocol Message Broker（ The message broker ）. There are many on the market Message Broker Software , Such as ActiveMQ、RabbitMQ、Kafka etc. .

There are two main modes of messaging between services ： queue （Queue） And the theme （Topic）.

• Queue Mode is a one-to-one transmission mode . In this mode , Message producer （Producer） The destination type of message delivery for is Queue.Queue A message can only be delivered to one consumer （Consumer）, If no consumer is listening to the queue , Messages will remain in the queue , Until the message consumer connects to the queue , Consumers will request messages from the queue .

• Topic Mode is a one to many message transmission mode . In this mode , Message producer （Producer） The destination type of message delivery for is Topic. The news arrived Topic after , The message server sends messages to all consumers who subscribe to this topic .

At present, the main asynchronous messaging protocols in the industry are as follows .

• Java Messaging services （Java Messaging Service,JMS）, It faces Java Standard messaging for the platform API.

• Streaming text oriented message transfer protocol （Streaming Text Oriented Messaging Protocol,STOMP）：WebSocket Communication standards .

• Advanced message queue protocol （Advanced Message Queueing Protocol,AMQP）： Platform independent underlying messaging protocol , For integrating multi platform applications .

• Message queuing telemetry transmission （Message Queueing Telemetry Transport,MQTT）： It is designed for small silent devices to send short messages through low bandwidth . Use MQTT Can manage IoT equipment .

There are many kinds of message oriented middleware on the market ,Apache ActiveMQ Artemis Is the most popular open source 、 be based on Java The message server .ActiveMQ Artemis Support point-to-point messaging （Queue） And subscriptions / Release pattern （Topic）. Support standards Java NIO（New I/O, Synchronous non blocking mode ） and Linux AIO library （Asynchronous I/O, Asynchronous non-blocking I/O Model ）.AMQ Support multiple protocols , Include MQTT、STOMP、AMQP 1.0、JMS 1.1 and TCP.