Tutorial: Implement Sharding in Spring Boot by Using Spring Data

Verify the prerequisites

Before you begin, verify that you have the following:

• A MongoDB account. You need a cluster M30 or higher to enable sharding.

• Java 17 or later

• Maven version 3.9.6 or later

• A Spring Boot project with Spring Data MongoDB and Spring Web dependencies. You can create a project by using Spring Initializr.

• MongoDB Shell

Set up a sharded cluster in MongoDB Atlas

To create a sharded cluster, perform the following actions:

1. In the cluster settings of your M30 or higher cluster, navigate to Additional Settings.

2. Select Sharding and toggle it on.

3. Set the number of shards to deploy. For production applications, use more than one shard. You can deploy between 1 and 70 shards. To learn more, see the Deploy a Sharded Cluster in the Atlas documentation.

4. Once your sharded cluster is created, select Load Sample Dataset to load the sample data.

Configure sharding for a collection

Spring Data MongoDB does not automatically configure sharding for collections. You must perform these operations manually by using mongosh.

To connect to your cluster and configure sharding, run the following command in your terminal:

mongosh "mongodb+srv://<username>:<password>@<cluster-url>/admin"

Replace the <username>, <password>, and <cluster-url> placeholders with your MongoDB Atlas credentials and connection string.

To shard the users collection by the email field, run the following command:

sh.shardCollection("sample_mflix.users", { email: 1 })

To verify that sharding is enabled and the collection is sharded, run the following command:

sh.status()

Implement the Spring Boot application

To implement the Spring Boot application, you must define the entity, repository, service, and controller layers.

1. To define an entity class with sharding, use the @Sharded annotation to specify the shard key fields. The following code shows an example User entity with the email field as the shard key:

   import org.springframework.data.annotation.Id;
   import org.springframework.data.mongodb.core.mapping.Document;
   import org.springframework.data.mongodb.core.mapping.Field;
   import org.springframework.data.mongodb.core.mapping.Sharded;
   @Document("users")
   @Sharded(shardKey = { "email" })
   public class User {
       @Id
       private String id;
       private String name;
       @Field("email")
       private String email;
       private String password;
       // Getters and Setters
   }

   The @Sharded annotation helps Spring Data MongoDB optimize operations in a sharded environment. It ensures that replaceOne queries include the shard key during upserts.

2. To create a repository for the User entity, define an interface that extends MongoRepository. The following code shows an example UserRepository interface:

   import org.springframework.data.mongodb.repository.MongoRepository;
   import com.mongodb.sharded.model.User;
   public interface UserRepository extends MongoRepository<User, String> {
   }

3. To handle business logic, create a service class that interacts with the repository. The following code shows an example UserService class:

   import java.util.List;
   import org.springframework.beans.factory.annotation.Autowired;
   import org.springframework.stereotype.Service;
   import com.mongodb.sharded.model.User;
   import com.mongodb.sharded.repository.UserRepository;
   @Service
   public class UserService {
       @Autowired
       private UserRepository userRepository;
       public List<User> getAllUsers() {
           return userRepository.findAll();
       }
       public User saveUser(User user) {
           return userRepository.save(user);
       }
   }

4. To expose REST endpoints for the User entity, create a controller class. The following code shows an example UserController class:

   import org.springframework.beans.factory.annotation.Autowired;
   import org.springframework.web.bind.annotation.*;
   import java.util.List;
   @RestController
   @RequestMapping("/users")
   public class UserController {
       @Autowired
       private UserService userService;
       @GetMapping
       public List<User> getAllUsers() {
           return userService.getAllUsers();
       }
       @PostMapping
       public User createUser(@RequestBody User user) {
           return userService.saveUser(user);
       }
   }

Configure the Spring Boot application

To connect your Spring Boot application to MongoDB Atlas, add the MongoDB connection URI to your application.properties or application.yml file. The following code shows an example configuration:

spring.data.mongodb.uri=mongodb+srv://<username>:<password>@<cluster-url>/myDatabase?retryWrites=true&w=majority

Replace the <username>, <password>, and <cluster-url> placeholders with your MongoDB Atlas credentials and connection string.