Configuration Loading Process

Loading process for dubbo configuration

Monday, January 01, 0001

This document focuses on how the Dubbo framework collects the required configuration (including application configuration, registry configuration, service configuration, etc.) during the application startup phase to complete the process of service exposure and reference.

Depending on how you drive it (such as Spring or naked API programming), the configuration form will certainly vary, for detail please refer to XML Configuration, Annotation Configuration and API Configuration. In addition to the differences in peripheral drivers, Dubbo’s configuration reads generally follow the following principles:

Dubbo supports multiple levels of configuration and automatically override configurations according to predetermined priorities. Eventually, all configurations are aggregated to the data bus URL to drive subsequent service exposure, reference and other processes.
ApplicationConfig, ServiceConfig and ReferenceConfig can be regarded as configuration sources, which collect configuration by directly user-oriented programming.
The configuration format is mainly Properties, and the configuration content follows conventions
The configuration format is mainly Properties, and the configuration content follows the agreed path-based naming [specification](#Configuration Format).

Configuration Source

First, starting with the configuration sources that Dubbo supports, there are four default configuration sources:

JVM System Properties，-Dproperty
Externalized Configuration
ServiceConfig, ReferenceConfig and other programming interface collected configuration
Local configuration file dubbo.properties

Override Priority

The figure below shows the priority of configuration override, decreasing from top to bottom:

Override Priority

click here to view Externalize configuration details

Configuration Format

Currently, all configurations supported by Dubbo are in the format of .properties, including -D, Externalized Configuration, etc., and all configuration items in .properties follow a path-based Configuration format:

# Application level
dubbo.{config-type}[.{config-id}].{config-item}={config-item-value}
# Service level
dubbo.service.{interface-name}[.{method-name}].{config-item}={config-item-value}
dubbo.reference.{interface-name}[.{method-name}].{config-item}={config-item-value}
# Multiple configuration items
dubbo.{config-type}s.{config-id}.{config-item}={config-item-value}

Application level

dubbo.application.name=demo-provider
dubbo.registry.address=zookeeper://127.0.0.1:2181
dubbo.protocol.port=-1

Service level

dubbo.service.org.apache.dubbo.samples.api.DemoService.timeout=5000
dubbo.reference.org.apache.dubbo.samples.api.DemoService.timeout=6000
dubbo.reference.org.apache.dubbo.samples.api.DemoService.sayHello.timeout=7000

Multiple configuration items

dubbo.registries.unit1.address=zookeeper://127.0.0.1:2181
dubbo.registries.unit2.address=zookeeper://127.0.0.1:2182

dubbo.protocols.dubbo.name=dubbo
dubbo.protocols.dubbo.port=20880
dubbo.protocols.hessian.name=hessian
dubbo.protocols.hessian.port=8089

Extended configuration

dubbo.application.parameters.item1=value1
dubbo.application.parameters.item2=value2
dubbo.registry.parameters.item3=value3
dubbo.reference.org.apache.dubbo.samples.api.DemoService.parameters.item4=value4

Several programming approaches of configuration

Next, let’s look at the changes corresponding to ServiceConfig, ReferenceConfig and other programming interface collected configuration when selecting different development methods.

Spring

Refer to the sample

  <!-- dubbo-provier.xml -->
  
  <dubbo:application name="demo-provider"/>
  <dubbo:config-center address="zookeeper://127.0.0.1:2181"/>
  
  <dubbo:registry address="zookeeper://127.0.0.1:2181" simplified="true"/>
  <dubbo:metadata-report address="redis://127.0.0.1:6379"/>
  <dubbo:protocol name="dubbo" port="20880"/>
  
  <bean id="demoService" class="org.apache.dubbo.samples.basic.impl.DemoServiceImpl"/>
  <dubbo:service interface="org.apache.dubbo.samples.basic.api.DemoService" ref="demoService"/>

Annotation

Refer to the sample

  // AnnotationService implementation
  
  @Service
  public class AnnotationServiceImpl implements AnnotationService {
      @Override
      public String sayHello(String name) {
          System.out.println("async provider received: " + name);
          return "annotation: hello, " + name;
      }
  }

  ## dubbo.properties
  
  dubbo.application.name=annotation-provider
  dubbo.registry.address=zookeeper://127.0.0.1:2181
  dubbo.protocol.name=dubbo
  dubbo.protocol.port=20880

Spring Boot

Refer to the sample

  ## application.properties
  
  # Spring boot application
  spring.application.name=dubbo-externalized-configuration-provider-sample
  
  # Base packages to scan Dubbo Component: @com.alibaba.dubbo.config.annotation.Service
  dubbo.scan.base-packages=com.alibaba.boot.dubbo.demo.provider.service
  
  # Dubbo Application
  ## The default value of dubbo.application.name is ${spring.application.name}
  ## dubbo.application.name=${spring.application.name}
  
  # Dubbo Protocol
  dubbo.protocol.name=dubbo
  dubbo.protocol.port=12345
  
  ## Dubbo Registry
  dubbo.registry.address=N/A
  
  ## DemoService version
  demo.service.version=1.0.0

API

public static void main(String[] args) throws IOException {
    ServiceConfig<GreetingsService> service = new ServiceConfig<>();
    service.setApplication(new ApplicationConfig("first-dubbo-provider"));
    service.setRegistry(new RegistryConfig("multicast://224.5.6.7:1234"));
    service.setInterface(GreetingsService.class);
    service.setRef(new GreetingsServiceImpl());
    service.export();
    System.out.println("first-dubbo-provider is running.");
    System.in.read();
}

Refer to the sample