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Pattern: Messaging


You have applied the Microservice architecture pattern. Services must handle requests from the application’s clients. Furthermore, services must sometimes collaborate to handle those requests. They must use an inter-process communication protocol.



Use asynchronous messaging for inter-service communication. Services communicating by exchanging messages over messaging channels.


There are numerous examples of asynchronous messaging technologies

UserRegistrationController from the Microservices Example application is an example of a component, which is written in Scala, that sends a message via RabbitMQ using the Spring Framework’s RabbitTemplate:

class UserRegistrationController @Autowired()(registeredUserRepository: RegisteredUserRepository, rabbitTemplate: RabbitTemplate) {

  import MessagingNames._

  @RequestMapping(value = Array("/user"), method = Array(RequestMethod.POST))
  def registerUser(@Validated @RequestBody request: RegistrationRequest) = {
    val registeredUser = new RegisteredUser(null, request.emailAddress, request.password)
    rabbitTemplate.convertAndSend(exchangeName, routingKey, NewRegistrationNotification(registeredUser.id, request.emailAddress, request.password))
    RegistrationResponse(registeredUser.id, request.emailAddress)

  @ResponseStatus(value = HttpStatus.CONFLICT, reason = "duplicate email address")
  def duplicateEmailAddress() {}


Resulting context

This pattern has the following benefits:

  • Loose coupling since it decouples client from services
  • Improved availability since the message broker buffers messages until the consumer is able to process them
  • Supports a variety of communication patterns including request/reply, notifications, request/async response, publish/subscribe, publish/async response etc

This pattern has the following drawbacks:

  • Additional complexity of message broker, which must be highly available

This pattern has the following issues:

  • Request/reply-style communication is more complex
  • Client needs to discover location of message broker

See also

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