Creating a Multi-Tenant Application with CodeIgniter: A Complete Guide

Building a multi-tenant application allows you to serve multiple customers (tenants) from a single codebase. This is the backbone of modern SaaS (Software as a Service) products. In this guide, we will explore the best strategies for implementing multi-tenancy in CodeIgniter to reduce overhead and improve scalability.

What is Multi-Tenancy in Web Applications?

Multi-tenancy is an architecture where a single instance of a software application serves multiple independent tenants. While tenants share the same infrastructure, their data is strictly isolated. Think of it as an apartment building: the structure is shared, but every tenant has their own private space.

Why Use CodeIgniter for SaaS?

• Lightweight Performance: CodeIgniter 4 is exceptionally fast, which is crucial when handling multiple tenants.
• Flexibility: It doesn't force a specific structure, allowing you to implement custom isolation logic.
• Easy Configuration: Dynamically changing database connections is straightforward in CI4.

Top 3 Multi-Tenancy Database Strategies

Choosing the right database architecture is the most important decision in a CodeIgniter multi-tenant project.

1. Separate Database per Tenant

Each tenant has a completely different database.

• Pros: Maximum security and data isolation.
• Cons: Higher management overhead (migrations must run on all DBs).
• Best for: Enterprises with strict data compliance needs.

2. Shared Database, Separate Schemas

Tenants share a database server but have unique logical schemas.

• Pros: Good balance between isolation and resource usage.
• Cons: Not supported by all database engines (e.g., MySQL doesn't use schemas like PostgreSQL).

3. Shared Database, Shared Schema (The "Tenant ID" Approach)

All tenants share the same tables, but a tenant_id column distinguishes the data.

• Pros: Easiest to scale and maintain.
• Cons: Requires careful coding to ensure one tenant cannot see another's data.
• Implementation: Use CodeIgniter Models to automatically filter queries by tenant_id.

How to Identify Tenants in CodeIgniter

You must determine which tenant is accessing the site before loading any data. Common strategies include:

1. Subdomain-based: client-a.your-saas.com (Professional and SEO-friendly).
2. Path-based: your-saas.com/client-a (Easier to set up without DNS changes).
3. Header-based: Used primarily for mobile apps or headless APIs.

Implementation Tip: Middleware Identification

In CodeIgniter 4, use Filters to intercept the request and set the tenant context globally:

Step-by-Step Implementation Strategy

1. Master Database: Maintain one central database to store tenant credentials and their specific configuration (e.g., custom colors, database names).
2. Dynamic Connection Switching: If using separate databases, use the Config\Database::connect() method to switch connections on the fly based on the tenant identified in the filter.
3. Automated Migrations: Use a custom CLI command to loop through all tenant databases and run migrations simultaneously.
4. Scoped File Storage: Ensure file uploads are stored in tenant-specific folders: writable/uploads/tenant_1/.

Conclusion

Building a multi-tenant application with CodeIgniter is a powerful way to launch a SaaS product. Whether you choose a shared database for simplicity or separate databases for security, CodeIgniter provides the tools to manage tenant isolation effectively.