Dubbo as a lightweight RPC framework solves component communication issues on Apache Dubbo

Generic Implementation

Mon, 01 Jan 0001 00:00:00 +0000

Note

Please distinguish between the previous document on Generic Invocation, which is for consumers, and Generic Implementation, which is for providers.

The generic interface implementation method is mainly used in scenarios where the server side does not have API interfaces and model class metadata. All POJOs in parameters and return values are represented using Map, usually for framework integration. For example, to implement a generic remote service Mock framework, you can handle all service requests by implementing the GenericService interface.

Echo Testing

Mon, 01 Jan 0001 00:00:00 +0000

Feature Description

Echo testing is used to detect whether a service is available. The echo test follows the normal request process, allowing the entire call to be tested for smooth operation and can be used for monitoring. In an echo test, the client sends a request containing a specific value (such as a string). The server should respond with the same value to verify that the request has been successfully received and processed. If the response does not match the request, it indicates that the service is not functioning properly and further investigation is needed. It requires that the Dubbo server is running and that there is a network connection between the server and the client. On the client side, the Dubbo client must be configured to connect to the server, which will send requests to the server, and then the server should return the same response as the request.

Dynamically Specify IP Call

Mon, 01 Jan 0001 00:00:00 +0000

Feature Description

When initiating an RPC request, it is necessary to specify the server for this call. Common scenarios include message callbacks, traffic isolation, etc.

Usage

Plugin Dependency

First, add the following plugin dependency to your project

<dependency>
 <groupId>org.apache.dubbo.extensions</groupId>
 <artifactId>dubbo-cluster-specify-address-dubbo3</artifactId>
 <version>3.3.0</version>
</dependency>

For Dubbo 2 version

<dependency>
 <groupId>org.apache.dubbo.extensions</groupId>
 <artifactId>dubbo-cluster-specify-address-dubbo2</artifactId>
 <version>1.0.0</version>
</dependency>

Call Example

ReferenceConfig<DemoService> referenceConfig = new ReferenceConfig<>();
// ... init
DemoService demoService = referenceConfig.get();

// for invoke
// 1. find 10.10.10.10:20880 exist
// 2. if not exist, create a invoker to 10.10.10.10:20880 if `needToCreate` is true (only support in Dubbo 3.x's implementation)
UserSpecifiedAddressUtil.setAddress(new Address("10.10.10.10", 20880, true));
demoService.sayHello("world");


// for invoke
// 1. find 10.10.10.10:any exist
// 2. if not exist, create a invoker to 10.10.10.10:20880 if `needToCreate` is true (only support in Dubbo 3.x's implementation)
UserSpecifiedAddressUtil.setAddress(new Address("10.10.10.10", 0, true));
demoService.sayHello("world");

Parameter Description

The parameters for specifying IP calls revolve around the Address object. The parameter types are as follows:

Direct Connection Provider

Mon, 01 Jan 0001 00:00:00 +0000

In development and testing environments, it is often necessary to bypass the registry and only test specific service providers. In this case, point-to-point direct connection may be required. The point-to-point direct connection method will ignore the provider list from the registry on a service interface basis. Configuring point-to-point for interface A will not affect interface B from obtaining the list from the registry.

If point-to-point communication is needed in a production environment, you can configure the reference node to point to the provider URL, bypassing the registry. Multiple addresses can be separated by semicolons, configured as follows:

Event Notifications Triggered by Calls

Mon, 01 Jan 0001 00:00:00 +0000

Feature Description

The events oninvoke, onreturn, and onthrow will be triggered before a call, after a call, and when an exception occurs, respectively. You can configure which class and method to notify when these events happen.

Use Cases

Before calling the service method, we can log the start time, after the call, calculate the total time consumed, and in case of exceptions, we can trigger alerts or print error logs, or log request and response logs before and after the service call.

Server Callback to Client

Mon, 01 Jan 0001 00:00:00 +0000

Feature Description

The callback parameter method is similar to calling a local callback or listener; you only need to declare which parameter is a callback type in the Spring configuration file. Dubbo will generate a reverse proxy based on a long connection, allowing the server to invoke client logic. You can refer to the example code in the dubbo project.

Use Case

The callback function informs the client of execution results or sends notifications, functioning similarly to asynchronous calls when method execution times are long, such as in approval workflows where the client is notified of approval results.

Service Explanation (Local Mock)

Mon, 01 Jan 0001 00:00:00 +0000

Feature Description

In Dubbo3, there is a mechanism for lightweight service downgrading, that is, local mocking.

Mock is a subset of Stub, facilitating service providers to implement fault tolerance logic on the client side. It is often necessary to handle exceptions during RpcException (e.g., network failures, timeouts), while fault tolerance is not needed for business exceptions (e.g., login username/password errors). Using Stub may require capturing and depending on RpcException, whereas Mock does not, since its agreement is to only execute when RpcException occurs.

Local Stub

Mon, 01 Jan 0001 00:00:00 +0000

Feature Description:

After invoking a remote service, the client typically only has the interface, while the implementation resides entirely on the server. However, sometimes the provider wants to execute part of the logic on the client side as well.

Usage Scenarios

For scenarios such as creating ThreadLocal caches, validating parameters in advance, or simulating fault tolerance data after a failed call, the API needs to have a Stub. The client generates a Proxy instance, which is passed to the Stub through the constructor ¹, and then the Stub is exposed to the user. The Stub can decide whether to invoke the Proxy.

Local Call

Mon, 01 Jan 0001 00:00:00 +0000

Feature Description

Local calls use the injvm protocol, which is a pseudo-protocol that does not open a port or initiate remote calls; it directly associates within the JVM but executes the Dubbo filter chain.

Usage Scenarios

When we need to call a remote service that is not yet developed, we can implement a similar service locally using the injvm protocol, allowing us to invoke our local implementation of the service.

Concurrency Control

Mon, 01 Jan 0001 00:00:00 +0000

Function Description

Multiple concurrency control features help users manage their applications and services.

Use Cases

Limit the number of concurrent requests from the same client to the same service, preventing malicious requests from overloading the server, ensuring service stability, and preventing excessive resource usage.

Control the maximum number of concurrent requests for certain services, ensuring the availability of resources for other services. System overload and ensuring system stability.

Allow for smoother scaling of services when demand increases.

Connection Control

Mon, 01 Jan 0001 00:00:00 +0000

Function Description

The connection control feature allows users to manage and control the number of incoming and outgoing connections to the server, limit the number of connections, and set timeouts, ensuring the stability and performance of the Dubbo system. It also allows users to configure different levels of access control based on IP address, port, and protocol to protect the system from malicious traffic and reduce the risk of service interruptions. Additionally, it provides a way to monitor current traffic and connection status.

Host Configuration

Mon, 01 Jan 0001 00:00:00 +0000

Background

In Dubbo, when a Provider starts, it does two main things: it starts the server and registers the service with the registry. When starting the server, it needs to bind the socket, and when registering the service with the registry, it also needs to send the socket’s unique identifier as the service address.

What is the default host when host is not set in dubbo?
How do we specify the service’s host in dubbo, can we use a hostname or domain instead of an IP address as host?
When using Docker, sometimes port mapping needs to be set, in this case, how should we set the socket bound during server startup and the socket registered with the registry to use different port numbers?

Example

What is the default host when host is not set in dubbo

The general dubbo protocol configuration is as follows:

Result Cache Invocation

Mon, 01 Jan 0001 00:00:00 +0000

Function Description

Dubbo supports server-side and client-side result caching.

Cache Types

Currently, versions 3.0 and above of Dubbo support the following built-in caching strategies:

lru removes excess cache based on the least recently used principle, keeping the hottest data cached.
lfu implements cache strategy based on the principle of evicting the least frequently used.
expiring implements cache strategy based on expiration time.
threadlocal caches in the current thread, for example in a page render when many portals are needed to query user information, using thread cache can reduce such unnecessary accesses.
jcache integrates with JSR107, bridging various cache implementations.

Cache types are extensible Cache Extension

Route Status Collection

Mon, 01 Jan 0001 00:00:00 +0000

Function Description

The route status collection feature can be used to identify any potential issues that may affect service performance, to identify any potential bottlenecks or problems that may hinder the efficient use of services, ensuring smooth operation of services, and that users do not encounter any issues when trying to access services. It allows users to check whether the route is enabled or disabled, ensuring that only authorized services are used and access is limited to authorized personnel.

Service Reference Configuration Object Cache

Mon, 01 Jan 0001 00:00:00 +0000

Function Description

ReferenceConfig instances are heavy because they encapsulate the connections to the registry and the providers, necessitating caching. Otherwise, repeatedly generating ReferenceConfig can lead to performance issues and memory and connection leaks. This problem is often overlooked in API-oriented programming.

Therefore, starting from version 2.4.0, Dubbo provides a simple utility class ReferenceConfigCache for caching ReferenceConfig instances.

Usage Scenarios

In scenarios such as gateways where subscriptions are dynamically created, the ReferenceConfig itself is heavy and creates many intermediate objects, while the proxy can be reused. Hence, ReferenceConfigCache can cache these properties.

Parameter Validation

Mon, 01 Jan 0001 00:00:00 +0000

Feature Description

The parameter validation feature is implemented based on JSR303. Users only need to specify validation annotations from the JSR303 standard and implement validation through a declared filter.

Maven Dependency

<dependency>
 <groupId>javax.validation</groupId>
 <artifactId>validation-api</artifactId>
 <version>1.0.0.GA</version>
</dependency>
<dependency>
 <groupId>org.hibernate</groupId>
 <artifactId>hibernate-validator</artifactId>
 <version>4.2.0.Final</version>
</dependency>

Usage Scenario

The server addresses various interface parameter validation issues when providing interface services externally.

Reference Case https://github.com/apache/dubbo-samples/tree/master/dubbo-samples-validation

Usage Method

Parameter Annotation Example

import java.io.Serializable;
import java.util.Date;
 
import javax.validation.constraints.Future;
import javax.validation.constraints.Max;
import javax.validation.constraints.Min;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Past;
import javax.validation.constraints.Pattern;
import javax.validation.constraints.Size;
 
public class ValidationParameter implements Serializable {
 private static final long serialVersionUID = 7158911668568000392L;
 
 @NotNull // Cannot be null
 @Size(min = 1, max = 20) // Length or size range
 private String name;
 
 @NotNull(groups = ValidationService.Save.class) // Cannot be null when saving, can be null when updating, indicating no update to this field
 @Pattern(regexp = "^\\s*\\w+(?:\\.{0,1}[\\w-]+)*@[a-zA-Z0-9]+(?:[-.][a-zA-Z0-9]+)*\\.[a-zA-Z]+\\s*$")
 private String email;
 
 @Min(18) // Minimum value
 @Max(100) // Maximum value
 private int age;
 
 @Past // Must be a past date
 private Date loginDate;
 
 @Future // Must be a future date
 private Date expiryDate;
 
 public String getName() {
 return name;
 }
 
 public void setName(String name) {
 this.name = name;
 }
 
 public String getEmail() {
 return email;
 }
 
 public void setEmail(String email) {
 this.email = email;
 }
 
 public int getAge() {
 return age;
 }
 
 public void setAge(int age) {
 this.age = age;
 }
 
 public Date getLoginDate() {
 return loginDate;
 }
 
 public void setLoginDate(Date loginDate) {
 this.loginDate = loginDate;
 }
 
 public Date getExpiryDate() {
 return expiryDate;
 }
 
 public void setExpiryDate(Date expiryDate) {
 this.expiryDate = expiryDate;
 }
}

Group Validation Example

public interface ValidationService { // Default can differentiate validation scenarios by service interface, e.g., @NotNull(groups = ValidationService.class) 
 @interface Save{} // Interface name same as method, capitalized first letter, used to differentiate validation scenarios, e.g., @NotNull(groups = ValidationService.Save.class), optional
 void save(ValidationParameter parameter);
 void update(ValidationParameter parameter);
}

import javax.validation.GroupSequence;
 
public interface ValidationService { 
 @GroupSequence(Update.class) // Validate Update group rules simultaneously
 @interface Save{}
 void save(ValidationParameter parameter);
 
 @interface Update{} 
 void update(ValidationParameter parameter);
}

Parameter Validation Example

import javax.validation.constraints.Min;
import javax.validation.constraints.NotNull;
 
public interface ValidationService {
 void save(@NotNull ValidationParameter parameter); // Validate parameter is not null
 void delete(@Min(1) int id); // Directly validate basic type parameter
}

Validate Parameters on Client

<dubbo:reference id="validationService" interface="org.apache.dubbo.examples.validation.api.ValidationService" validation="true" />

Validate Parameters on Server

<dubbo:service interface="org.apache.dubbo.examples.validation.api.ValidationService" ref="validationService" validation="true" />

Dubbo supports hibernate-validator version <=6.x by default. If using hibernate-validator version 7.x, declare the validation parameter as jvalidationNew.

Reactive Programming

Mon, 01 Jan 0001 00:00:00 +0000

Outdated Risk Reminder

Please note that the Reactive usage methods described in this document may be outdated. Always refer to the latest reactive examples in apache/dubbo-samples for usage.

Feature Description

This feature is based on the Triple protocol and implemented using Project Reactor, supported from version 3.1.0 onwards. Users only need to write an IDL file and specify the corresponding Generator for the protobuf plugin to generate and use Stub code that supports the reactive API.

Dubbo as a lightweight RPC framework solves component communication issues on Apache Dubbo

Generic Implementation

Note

Echo Testing

Feature Description

Dynamically Specify IP Call

Feature Description

Usage

Plugin Dependency

Call Example

Parameter Description

Direct Connection Provider

Event Notifications Triggered by Calls

Feature Description

Use Cases

Server Callback to Client

Feature Description

Use Case

Service Explanation (Local Mock)

Feature Description

Local Stub

Feature Description:

Usage Scenarios

Local Call

Feature Description

Usage Scenarios

Concurrency Control

Function Description

Use Cases

Connection Control

Function Description

Host Configuration

Background

Example

What is the default host when host is not set in dubbo

Result Cache Invocation

Function Description

Cache Types

Route Status Collection

Function Description

Service Reference Configuration Object Cache

Function Description

Usage Scenarios

Parameter Validation

Feature Description

Maven Dependency

Usage Scenario

Usage Method

Parameter Annotation Example

Group Validation Example

Related Validation Example

Parameter Validation Example

Validate Parameters on Client

Validate Parameters on Server

Reactive Programming

Outdated Risk Reminder

Feature Description