This example illustrates how to use Nacos Discovery Starter implement Service discovery for Spring Cloud applications.
[Nacos](https://github.com/alibaba/Nacos) an easy-to-use dynamic service discovery, configuration and service management platform for building cloud native applications.
## Demo
### Connect to Nacos Discovery
Before we start the demo, let's learn how to connect Nacos Config to a Spring Cloud application. **Note: This section is to show you how to connect to Nacos Discovery. The configurations have been completed in the following example, so you don't need modify the code any more.**
1. Add dependency spring-cloud-starter-alibaba-nacos-discovery in the pom.xml file in your Spring Cloud project.
1. Install Nacos Server by downloading or build from source code.**Recommended latest version Nacos Server**
1. Download: Download Nacos Server [download page](https://github.com/alibaba/nacos/releases)
2. Build from source code: Get source code by git clone git@github.com:alibaba/Nacos.git from Github Nacos and build your code. See [build reference](https://nacos.io/en-us/docs/quick-start.html) for details.
2. Unzip the downloaded file and go to the nacos/bin folder(), And according to the actual situation of the operating system, execute the following command。[see reference for more detail](https://nacos.io/en-us/docs/quick-start.html)。
1. Add necessary configurations to project `nacos-discovery-provider-example`, file /src/main/resources/application.properties.
spring.application.name=service-provider
server.port=18082
2. Start the application in IDE or by building a fatjar.
1. Start in IDE: Find main class `ProviderApplication ` in project `nacos-discovery-provider-example`, and execute the main method.
2. Build a fatjar：Execute command `mvn clean package` in project ` nacos-discovery-provider-example ` to build a fatjar，and run command `java -jar nacos-discovery-provider-example.jar` to start the application.
Enter `http://127.0.0.1:8848/nacos/#/serviceDetail?name=service-provider&groupName=DEFAULT_GROUP` in the browser address bar and click Go to, we can see that the service node has been successfully registered to Nacos Server.
Add the following configuration to use the load balancing strategy provided by the Spring Cloud Alibaba community for Spring Cloud Loadbalancer load balancing dependencies, so as to use all the capabilities provided by Spring Cloud Alibaba:
```properties
spring.cloud.loadbalancer.ribbon.enabled=false
spring.cloud.loadbalancer.nacos.enabled=true
```
#### IPv4 to IPv6 address migration scheme
##### Both register IPv4 and IPv6 address
After configuring above Spring Cloud Loadbalancer as the load balancing policy, the IPv4 address and IPv6 address of the microservice will be registered with the registry by default after the application is started, where the IPv4 address will be stored in the IP field of the Nacos service list, the IPv6 address will be in the metadata field of Nacos, and its corresponding Key will be IPv6. When a service consumer calls a service provider, it selects the appropriate IP address type to initiate a service call based on its IP address stack support. Specific rules:
(1) If the service consumer itself supports IPv4 and IPv6 dual address stacks or only supports IPv6 address stacks, the service consumer will use the IPv6 address provided by the service to initiate a service call, and if the IPv6 address call fails, if it also supports the IPv4 address stack, it is temporarily not supported to switch to IPv4 and then initiate a retry call;
(2) If the service consumer itself only supports IPv4 single-address stack, the service consumer will use the IPv4 address provided by the service to initiate service calls.
##### Only Register IPv4 address
If you only want to register IPv4 address.Config in application.properties as follows:
```
spring.cloud.nacos.discovery.ip-type=IPv4
```
##### Only Register IPv6 address
If you only want to register IPv6 address.Config in application.properties as follows:
The code of `nacos-discovery-consumer-example` project will be analyzed below, demonstrating how RestTemplate and FeignClient.
**Note This section is to show you how to connect to Nacos Discovery. The configurations have been completed in the following example, so you don't need modify the code any more.Only the contents related to Ribbon, RestTemplate, and FeignClient are involved here. If other service discovery components have been used, you can access Nacos Discovery by directly replacing the dependencies.**
1. Add the @LoadBlanced annotation to make RestTemplate accessible to the Ribbon
@Bean
@LoadBalanced
public RestTemplate restTemplate() {
return new RestTemplate();
}
1. FeignClient has integrated the Ribbon by default, which shows how to configure a FeignClient.
Use the @FeignClient annotation to wrap the `EchoService` interface as a FeignClient with the attribute name corresponding to the service name `service-provider`.
The `@RequestMapping` annotation on the `echo` method corresponds the echo method to the URL `/echo/{str}`, and the `@PathVariable` annotation maps `{str}` in the URL path to the argument `str` of the echo method.
1. After completing the above configuration, injected them into the TestController.
1. Add necessary configurations to project `nacos-discovery-consumer-example` file /src/main/resources/application.properties.
spring.application.name=service-consumer
server.port=18083
1. Start the application in IDE or by building a fatjar.
1. Start in IDE: Find main class `ConsumerApplication ` in project `nacos-discovery-consumer-example`, and execute the main method.
2. Build a fatjar：Execute command `mvn clean package` in project ` nacos-discovery-consumer-example ` to build a fatjar，and run command `java -jar nacos-discovery-consumer-example.jar` to start the application.
#### Verification
1. Enter `http://127.0.0.1:18083/echo-rest/1234` in the browser address bar and click Go to, we can see that the browser displays the message "hello Nacos Discovery 1234" returned by nacos-discovery-provider-example to prove that the service discovery is in effect.
1. Enter `http://127.0.0.1:18083/echo-feign/12345` in the browser address bar and click Go to, we can see that the browser displays the message "hello Nacos Discovery 12345" returned by nacos-discovery-provider-example to prove that the service discovery is in effect.
Spring Cloud Nacos Discovery follows the spring cloud common standard and implements three interfaces: AutoServiceRegistration, ServiceRegistry, and Registration.
During the startup phase of the spring cloud application, the WebServerInitializedEvent event is watched. When the WebServerInitializedEvent event is received after the Web container is initialized, the registration action is triggered, and the ServiceRegistry register method is called to register the service to the Nacos Server.
As shown in the figure above, NacosDiscoveryProperties is the configuration of Nacos Discovery itself, and also includes the contents registered by the application, subscribe is the service information that the application has subscribed to.
## More
#### More configuration items
Configuration item|key|default value|Description
----|----|-----|-----
server address|spring.cloud.nacos.discovery.server-addr||
ip type|spring.cloud.nacos.discovery.ip-type|Dual Stack Address|IPv4 and IPv6 can be configured, If there are multiple IP addresses of the same type of network card, and you want to specify a specific network segment address, you can use `spring.cloud.inetutils.preferred-networks` to configure the filter address.
network interface|spring.cloud.nacos.discovery.network-interface||When the IP is not configured, the registered IP address is the IP address corresponding to the network-interface. If this item is not configured, the address of the first network-interface is taken by default.
port|spring.cloud.nacos.discovery.port|-1|port to registry, Automatically detect without configuration
namesapce|spring.cloud.nacos.discovery.namespace||One of the common scenarios is the separation of the configuration of different environments, such as the development of the test environment and the resource isolation of the production environment.
[Nacos ](https://github.com/alibaba/Nacos) is committed to help you discover, configure, and manage your microservices. It provides a set of simple and useful features enabling you to realize dynamic service discovery, service configuration, service metadata and traffic management.
Nacos makes it easier and faster to construct, deliver and manage your microservices platform. It is the infrastructure that supports a service-centered modern application architecture with a microservices or cloud-native approach.
If you have any ideas or suggestions for Nacos Discovery starter, please don't hesitate to tell us by submitting github issues.
