问题
I'm currently working on a Spring Boot microservices project. I have created services and each service is running separately. With this, I need some services to communicate with other services. How can i achieve that?
I saw some blogs about this which use Netflix, Eureka cloud servers to achieve this. Is there any way I can achieve this in my local environment without using cloud servers?
回答1:
Of course you can. Microservices are just REST-Services. You need to understand how REST-Services work. After that just write 2 Microservices (2 Rest-Services: producer-service and consumer-service) with Spring-boot, let them run under different server-ports, call the consumer-service from the other, and that's it: you have your Microservices. Now this is the primitive way to write Microservices.
To make them evolve, you need to add some "magic" (no rocket science), for example using Ribbon to distribute load between two instances of your "producer-service".
You may use a discovery service which is just a spring-boot application with the annotation @EnableEurekaServer (You need to add the appropriate dependency in your pom)
Now add to your first (primitive) Microservices the annotation @EnableDiscoveryClient to the main classes and the defaultZone pointing to your eureka-service in the application.properties (or application.yml) of both, start your eureka-service (discovery service) and the 2 Microservices: those will register on the discovery-service. Of course now you don't need to hard-code the http address of the producer-service in the consumer-service.
Take a look at this tutorial
Edited on 21th of November 2018 at 12:41 GMT
Suppose that your first (trivial) microservice (a pure rest-service) is running on your PC under port 8091.
In the controller of your second (trivial) microservice you call your first service using the RestTemplate.getForEntity(url,responseType,uriVariables) like so for the example in the linked tutorial:
ResponseEntity<CurrencyConversionBean> responseEntity =
new RestTemplate().getForEntity(
"http://localhost:8091/currency-exchange/from/{from}/to/{to}", CurrencyConversionBean.class, uriVariables);
Where url: the url of your first (micro)(rest)service. responseType: the class/type of the object awaited as response. uriVariables: is a map containing variables for the URI template.
回答2:
There are different ways to communicate between microservices. But which one to use: depends on the usecase.
Api call: That is making actual rest api call to the other service usingRestTemplate,FeignClientetc as.
ResponseType obj= new RestTemplate().getForObject(URL, ResponseType.class, params);
- But what if the usecase is different, like, you have customer microservice and orders microservice both are using separate database . You have
customer nameand other details inordersdatabase as well. Once the customer update their name, you have to update the details in Orders database as well . How this can be done. ThroughAPI call? Then what if account microservice also needs this update. So Rest api will be an overhead. In this use case we can useMessageQueueslikeRabbitMQ. Customer microservice will create an event of customer update and which ever microservice is interested in this can subscribe.
Communication through message queue like RabbitMQ
Spring.io rabbit mq guide
回答3:
As mentioned by @g00glen00b in comments Eureka is not used for communication between microservices. Its for service discovery. There are two ways that I know ofthrough which you can communicate with other Microservices :
- RestTemplate
- Feign Client
RestTemplate is very simple to use. It does not require configurations.
e.g.
ResponseType obj= new RestTemplate().getForObject(URL, ResponseType.class, params);
url - the URL
responseType - the type of the return value
params- the variables to expand the template
Spring Doc link for your reference
来源：https://stackoverflow.com/questions/50506101/spring-boot-how-to-communicate-between-microservices