Implementing Multi-Tenancy in Spring Boot Applications

Multi-tenancy is a software architecture in which a single instance of an application serves multiple tenants, each with its own data and configuration. This is a common requirement for SaaS applications. In this article, we explore different strategies to implement multi-tenancy in Spring Boot.

1. Multi-Tenancy Strategies

There are three main approaches to implementing multi-tenancy:

1.1 Database Per Tenant

• Each tenant has its own database.

• Pros: Strong data isolation, better security.

• Cons: Increased maintenance and resource overhead.

1.2 Schema Per Tenant

• A single database with separate schemas for each tenant.

• Pros: Balanced isolation and maintainability.

• Cons: Limited by database schema constraints.

1.3 Shared Schema with Discriminator

• A single database and schema with a tenant_id column in tables.

• Pros: Low resource usage, easy to scale.

• Cons: Data security risks, complex query management.

2. Implementing Multi-Tenancy in Spring Boot

2.1 Configure Data Source Routing

Spring provides AbstractRoutingDataSource to dynamically route database connections based on the tenant.

Create a Tenant Context

public class TenantContext {
    private static final ThreadLocal<String> CURRENT_TENANT = new ThreadLocal<>();

    public static void setTenant(String tenant) {
        CURRENT_TENANT.set(tenant);
    }

    public static String getTenant() {
        return CURRENT_TENANT.get();
    }

    public static void clear() {
        CURRENT_TENANT.remove();
    }
}

Implement Routing DataSource

public class MultiTenantDataSource extends AbstractRoutingDataSource {
    @Override
    protected Object determineCurrentLookupKey() {
        return TenantContext.getTenant();
    }
}

2.2 Intercept Requests to Set Tenant

Use a Filter to extract the tenant from the request.

@WebFilter("/*")
public class TenantFilter implements Filter {
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) request;
        String tenantId = req.getHeader("X-Tenant-ID");
        if (tenantId != null) {
            TenantContext.setTenant(tenantId);
        }
        chain.doFilter(request, response);
        TenantContext.clear();
    }
}

3. Database Migrations for Multi-Tenant Applications

Managing database migrations in a multi-tenant environment can be challenging. Here’s how you can approach it:

3.1 Using Flyway or Liquibase

Tools like Flyway and Liquibase help manage schema changes efficiently.

Flyway Configuration for Schema Per Tenant

flyway.locations=classpath:db/migration/{tenantId}

Run migrations dynamically per tenant:

for (String tenant : tenantList) {
    Flyway flyway = Flyway.configure()
        .dataSource(getDataSourceForTenant(tenant))
        .load();
    flyway.migrate();
}

3.2 Handling Shared Schema Migrations

If using a shared schema, ensure all migrations account for the tenant_id column.

ALTER TABLE users ADD COLUMN tenant_id VARCHAR(255) NOT NULL;

Use a default schema versioning table with a tenant_id field to track applied migrations.

4. Securing Multi-Tenant Applications

• Use role-based access control (RBAC) to prevent cross-tenant access.

• Encrypt tenant-specific data for additional security.

• Log tenant activity separately to monitor access patterns.

• Implement row-level security policies in the database.

Conclusion

Implementing multi-tenancy in Spring Boot requires careful planning to balance isolation, performance, and maintainability. Choosing the right strategy depends on your application’s needs and scalability requirements.