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The patterns

How to apply the patterns

Core patterns

Decomposition

Deployment patterns

Cross cutting concerns

Communication style

External API

Service discovery

Reliability

Data management

Security

Testing

Observability

UI patterns


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Pattern: Messaging

Context

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.

Forces

Solution

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

Examples

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:

@RestController
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)
    registeredUserRepository.save(registeredUser)
    rabbitTemplate.convertAndSend(exchangeName, routingKey, NewRegistrationNotification(registeredUser.id, request.emailAddress, request.password))
    RegistrationResponse(registeredUser.id, request.emailAddress)
  }

  @ResponseStatus(value = HttpStatus.CONFLICT, reason = "duplicate email address")
  @ExceptionHandler(Array(classOf[DuplicateKeyException]))
  def duplicateEmailAddress() {}


}

Resulting context

This pattern has the following benefits:

  • decouples client from services
  • message broker buffers messages
  • supports a variety of communication patterns

This pattern has the following drawacks:

  • Additional complexity of message broker

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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