05-lab.md

Lab 5: Use Zookeeper for Distributed Configuration and Synchronization (Spring Boot 3.4.1)

Objective

Learn how to set up Apache Zookeeper to register microservices (Spring Boot 3.4.1) for discovery and explore its KV store for dynamic configuration. Zookeeper offers distributed synchronization capabilities suitable for microservices needing coordination or shared config.

---

Lab Steps

Part 1: Installing and Running Zookeeper

1. Download Zookeeper.

   • Visit Zookeeper Releases and download the latest stable release (e.g., zookeeper-3.8.2).

2. Extract the Zookeeper archive.

   • Windows:
     • Extract (e.g., apache-zookeeper-3.8.2-bin.tar.gz) into C:\Zookeeper.
   • macOS/Linux:
     • Extract:

       tar -xvzf apache-zookeeper-3.8.2-bin.tar.gz -C ~/Zookeeper

3. Set up the Zookeeper configuration.

   • In the conf folder:

     cp zoo_sample.cfg zoo.cfg

   • Edit zoo.cfg to set a valid data directory:

     dataDir=/path/to/Zookeeper/data

   • Create that directory:

     mkdir -p /path/to/Zookeeper/data

4. Start the Zookeeper server.

   • macOS/Linux example:

     cd ~/Zookeeper/apache-zookeeper-3.8.2-bin
     bin/zkServer.sh start

   • Windows (in Powershell or Command Prompt):

     cd C:\Zookeeper\apache-zookeeper-3.8.2-bin
     .\bin\zkServer.cmd

5. Verify Zookeeper is running.

   • Check status:

     bin/zkServer.sh status

   • It should say "standalone mode" and "running" if successful.

6. Test Zookeeper using the CLI.

   • Start the ZK shell:

     bin/zkCli.sh

   • Create a test node:

     create /config "Hello Zookeeper"

   • Retrieve the node value:

     get /config

   • Confirm it shows Hello Zookeeper.

---

Part 2: Setting Up the Zookeeper-Enabled Microservice

7. Generate a new Spring Boot project for ZookeeperService.

   • Visit https://start.spring.io/.
   • Configure:
     • Spring Boot Version: 3.4.1
     • Group Id: com.microservices
     • Artifact Id: zookeeper-service
     • Name: ZookeeperService
     • Package Name: com.microservices.zookeeperservice
     • Dependencies:
       • Spring Web
       • Spring Cloud Zookeeper Discovery
       • Spring Boot Actuator
   • Extract into ZookeeperService.

8. Import the project into your IDE.

9. Enable Zookeeper Discovery.

   • In ZookeeperServiceApplication.java:

     package com.microservices.zookeeperservice;
     
     import org.springframework.boot.SpringApplication;
     import org.springframework.boot.autoconfigure.SpringBootApplication;
     import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
     
     @SpringBootApplication
     @EnableDiscoveryClient
     public class ZookeeperServiceApplication {
         public static void main(String[] args) {
             SpringApplication.run(ZookeeperServiceApplication.class, args);
         }
     }

10. Configure Zookeeper in application.properties.

    • In src/main/resources/application.properties:

      spring.application.name=zookeeper-service
      spring.cloud.zookeeper.connect-string=localhost:2181
      server.port=8083

    • Port 2181 is the default Zookeeper port.

11. Add a REST endpoint.

    • In src/main/java/com/microservices/zookeeperservice/ZookeeperController.java:

      package com.microservices.zookeeperservice;
      
      import org.springframework.web.bind.annotation.GetMapping;
      import org.springframework.web.bind.annotation.RestController;
      
      @RestController
      public class ZookeeperController {
      
          @GetMapping("/zookeeper")
          public String getMessage() {
              return "Hello from Zookeeper Service!";
          }
      }

12. Run the ZookeeperService.

    • From the ZookeeperService directory:

      ./mvnw spring-boot:run

    • If everything works, Zookeeper logs should show registration of zookeeper-service.

13. Verify service registration.

    • Open another terminal:

      bin/zkCli.sh

    • Run:

      ls /services

    • You should see zookeeper-service.

---

Part 3: Adding Another Service

14. Generate a new Spring Boot project: ProductService.

    • Same approach:
      • Artifact Id: product-service
      • Name: ProductService
      • Package Name: com.microservices.productservice
      • Dependencies:
        • Spring Web
        • Spring Cloud Zookeeper Discovery
        • Spring Boot Actuator
    • Extract into ProductService.

15. Enable Zookeeper Discovery.

    • In ProductServiceApplication.java:

      package com.microservices.productservice;
      
      import org.springframework.boot.SpringApplication;
      import org.springframework.boot.autoconfigure.SpringBootApplication;
      import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
      
      @SpringBootApplication
      @EnableDiscoveryClient
      public class ProductServiceApplication {
          public static void main(String[] args) {
              SpringApplication.run(ProductServiceApplication.class, args);
          }
      }

16. Configure Zookeeper for ProductService.

    • In src/main/resources/application.properties:

      spring.application.name=product-service
      spring.cloud.zookeeper.connect-string=localhost:2181
      server.port=8084

17. Add a REST endpoint for ProductService.

    • In ProductController.java:

      package com.microservices.productservice;
      
      import org.springframework.web.bind.annotation.GetMapping;
      import org.springframework.web.bind.annotation.RestController;
      
      @RestController
      public class ProductController {
      
          @GetMapping("/products")
          public String getProducts() {
              return "List of products from Zookeeper!";
          }
      }

18. Run ProductService.

    • Similar to before:

      ./mvnw spring-boot:run

    • Check logs for any registration errors.

19. Verify ProductService in Zookeeper.

    • In the ZK CLI:

      ls /services

    • Should now list zookeeper-service and product-service.

---

Part 4: Testing Configuration Management

20. Update Zookeeper’s KV data.

    • In the ZK CLI:

      set /config "Updated Configuration Value"

    • This changes the node’s data at path /config.

21. Retrieve the updated configuration in ZookeeperService.

    • Modify ZookeeperController:

      package com.microservices.zookeeperservice;
      
      import org.springframework.beans.factory.annotation.Value;
      import org.springframework.web.bind.annotation.GetMapping;
      import org.springframework.web.bind.annotation.RestController;
      
      @RestController
      public class ZookeeperController {
      
          @Value("${config:Default Config}")
          private String configValue;
      
          @GetMapping("/config")
          public String getConfig() {
              return configValue;
          }
      }

22. Test the /config endpoint.

    • Access:

      http://localhost:8083/config
      

    • Should display Updated Configuration Value if /config node is read as a property.

---

Optional Exercises

1. Simulate service failures.

   • Kill one service. ZK should reflect it in the ephemeral node structure.

2. Add environment-specific configurations.

   • E.g., /config/dev vs. /config/prod. Use profiles or direct property binding to read them.

3. Integrate watchers.

   • Zookeeper watchers let you get notified of config changes in real-time.

---

Conclusion

By completing this lab, you have:

• Installed and ran Zookeeper locally.
• Registered multiple Spring Boot 3.4.1 services using Spring Cloud Zookeeper Discovery.
• Explored the KV store to set and retrieve dynamic configurations, which microservices can consume at runtime.
• Gained an understanding of how Zookeeper can provide service discovery and configuration management, similar to Eureka or Consul, but with additional synchronization primitives.