Load balancing with Zuul

Category : Microservices | Sub Category : Microservices | By Prasad Bonam Last updated: 2023-11-27 13:28:03 Viewed : 212

Zuul is a powerful API gateway and reverse proxy that can be used for load balancing in a microservices architecture. It is a part of the Netflix OSS (Open Source Software) suite and provides functionalities such as routing, filtering, and load balancing. Zuul works by sitting between clients and microservices, directing incoming requests to the appropriate service instances.

Load balancing with Zuul involves using the Zuul API gateway to distribute incoming requests among multiple instances of a microservice. Zuul acts as a reverse proxy, directing traffic to the appropriate service instances, thereby achieving load balancing. Here is an example and explanation of how to set up load balancing with Zuul using Spring Cloud and Eureka for service discovery.

Example Setup:

1. Create Microservices:

   Assume you have two microservices, user-service and order-service, each with multiple instances.

2. Enable Eureka Server:

   Set up a Eureka server for service registration and discovery. Include the following dependency in your Eureka server project:

   xmlCopy code
   <dependency>
       <groupId>org.springframework.cloud</groupId>
       <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
   </dependency>
   

   Enable the Eureka server in your main application class:

   javaCopy code
   import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;
   import org.springframework.boot.SpringApplication;
   import org.springframework.boot.autoconfigure.SpringBootApplication;
   
   @SpringBootApplication
   @EnableEurekaServer
   public class EurekaServerApplication {
       public static void main(String[] args) {
           SpringApplication.run(EurekaServerApplication.class, args);
       }
   }
   

3. Enable Eureka Client in Microservices:

   Enable the Eureka client in your user-service and order-service projects by including the following dependencies:

   xmlCopy code
   <dependency>
       <groupId>org.springframework.cloud</groupId>
       <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
   </dependency>
   

   Enable the Eureka client in your main application classes:

   javaCopy code
   import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
   import org.springframework.boot.SpringApplication;
   import org.springframework.boot.autoconfigure.SpringBootApplication;
   
   @SpringBootApplication
   @EnableEurekaClient
   public class UserServiceApplication {
       public static void main(String[] args) {
           SpringApplication.run(UserServiceApplication.class, args);
       }
   }
   

   Similar configuration for order-service.

4. Enable Zuul in the Gateway:

   In your Zuul Gateway project, include the Zuul dependency:

   xmlCopy code
   <dependency>
       <groupId>org.springframework.cloud</groupId>
       <artifactId>spring-cloud-starter-netflix-zuul</artifactId>
   </dependency>
   

   Enable Zuul in your main application class:

   javaCopy code
   import org.springframework.cloud.netflix.zuul.EnableZuulProxy;
   import org.springframework.boot.SpringApplication;
   import org.springframework.boot.autoconfigure.SpringBootApplication;
   
   @SpringBootApplication
   @EnableZuulProxy
   public class ZuulGatewayApplication {
       public static void main(String[] args) {
           SpringApplication.run(ZuulGatewayApplication.class, args);
       }
   }
   

5. Configure Zuul for Load Balancing:

   Configure Zuul in your application.properties or application.yml file:

   propertiesCopy code
   # Enable Eureka integration for service discovery
   eureka.client.enabled=true
   
   # Specify the list of service IDs that Zuul should route to
   zuul.routes.userservice.path=/users/**
   zuul.routes.userservice.serviceId=user-service
   zuul.routes.orderservice.path=/orders/**
   zuul.routes.orderservice.serviceId=order-service
   
   # Load balancing configuration (Round Robin by default)
   ribbon.eureka.enabled=true
   ribbon.eureka.listOfServers=http://user-service,http://order-service
   

Explanation:

• Eureka Server:

  • The Eureka server is responsible for service registration and discovery.
  • Microservices (user-service and order-service) register themselves with the Eureka server.
  • The Eureka server maintains a registry of available service instances.

• Eureka Client in Microservices:

  • Microservices act as Eureka clients and register with the Eureka server during startup.
  • Eureka clients periodically send heartbeats to the Eureka server to maintain their registration.

• Zuul Gateway:

  • The Zuul gateway is the entry point for external requests.
  • It uses Eureka for service discovery to locate available instances of the microservices.

• Zuul Configuration:

  • zuul.routes configuration specifies the mapping between paths and service IDs.
  • ribbon.eureka.listOfServers specifies the list of available service instances for load balancing.

• Load Balancing:

  • Zuul, by default, uses Ribbon as the client-side load balancer.
  • Ribbon supports various load balancing strategies (Round Robin by default).
  • Zuul distributes incoming requests among the available instances of the microservices using the configured load balancing strategy.

Testing:

1. Start the Eureka server.

2. Start multiple instances of user-service and order-service.

3. Start the Zuul gateway.

4. Make requests to the Zuul gateway:

   • http://localhost:8765/users/...
   • http://localhost:8765/orders/...

   Zuul will route the requests to the available instances of the corresponding microservices, demonstrating load balancing.

This setup allows for dynamic scaling and fault tolerance, as Eureka continuously monitors the health of service instances, and Zuul automatically adapts to changes in the available instances.

Load Balancing with Zuul - Components and Interactions:

1. Client:

   • Initiates a request to the system.
   • Sends the request to the Zuul Gateway.

2. Zuul Gateway:

   • Acts as an entry point for external requests.
   • Utilizes Eureka for service discovery to locate available instances of microservices.
   • Routes the incoming requests based on configuration.
   • Integrates with Ribbon for client-side load balancing.

3. Eureka Server:

   • Manages service registration and discovery.
   • Microservices register themselves with the Eureka server during startup.
   • Maintains a registry of available service instances.

4. Microservices (e.g., user-service, order-service):

   • Act as Eureka clients and register with the Eureka server.
   • Provide the actual business logic and functionality.
   • Multiple instances of each microservice may exist.

5. Ribbon (Client-Side Load Balancer):

   • Integrated with Zuul for load balancing.
   • Uses the information from Eureka to determine the available instances of microservices.
   • Distributes incoming requests among the available instances using a configured load balancing strategy (e.g., Round Robin).

Request Flow:

1. Client sends a request:

   • Requests are sent to the Zuul Gateway.

2. Zuul routes the request:

   • Zuul examines the request path and routes it based on the configured routes.
   • For example, requests to /users/** may be routed to the user-service.

3. Service Discovery (Eureka):

   • Zuul uses Eureka to discover available instances of the target microservice (e.g., user-service).

4. Load Balancing (Ribbon):

   • Ribbon, integrated with Zuul, performs client-side load balancing.
   • Distributes the incoming request among the available instances of the microservice.
   • Uses a load balancing strategy (e.g., Round Robin) to select an instance.

5. Microservice processes the request:

   • The selected instance of the microservice processes the request and sends the response back to Zuul.

6. Zuul sends the response to the client:

   • Zuul receives the response from the microservice and forwards it to the client.

Notes:

• This architecture allows for dynamic scaling of microservices as new instances can be registered with Eureka, and Zuul will automatically route requests to them.
• Load balancing ensures even distribution of requests among available instances, improving system reliability and scalability.
• Fault tolerance is achieved as Eureka continuously monitors the health of service instances, and Zuul adapts to changes in the available instances.

For a visual representation, you can use tools like draw.io, Lucidchart, or any preferred drawing tool to create a diagram based on the described components and interactions.