Multi-Tenant Architecture

🏢 Multi-Tenant Architecture: The Apartment Building of Cloud Computing

Imagine you’re building the world’s biggest apartment complex. Hundreds of families will live there, each with their own space, their own keys, and their own privacy. But they all share the same building, the same elevators, and the same water pipes.

That’s exactly what Multi-Tenant Architecture is!

🎯 What You’ll Learn

• How applications are built in three layers (like a three-layer cake!)
• What multi-tenancy means (sharing smartly)
• How to keep everyone’s stuff separate and safe
• When to share vs when to give someone their own space

🍰 Three-Tier Architecture: The Three-Layer Cake

Think of building an app like baking a cake with three layers. Each layer has a special job!

Layer 1: Presentation Tier (The Frosting)

What the user sees and touches.

This is the pretty part! The buttons you click, the pictures you see, the forms you fill out.

🎨 Example: When you open Netflix, the screen showing all those movie posters? That’s the presentation tier!

Layer 2: Application Tier (The Cake)

Where the thinking happens.

This is the brain! It takes your requests, figures out what to do, and makes decisions.

🧠 Example: When you search “funny cat videos,” this layer finds all matching videos and sorts them for you.

Layer 3: Data Tier (The Plate)

Where everything is stored.

This is the memory! All your saved information, your watchlist, your preferences.

💾 Example: Your Netflix password, your viewing history, your profile picture — all stored here!

graph TD
    A["👤 You Click a Button"] --> B["🎨 Presentation Tier"]
    B --> C["🧠 Application Tier"]
    C --> D["💾 Data Tier"]
    D --> C
    C --> B
    B --> A

Why Three Layers?

🏠 Multi-Tenancy: Sharing an Apartment Building

Tenant = A customer using your app (like a family in an apartment)

Multi-Tenancy = Many customers sharing one system (many families, one building)

The Apartment Building Analogy

Imagine you own an apartment building. You could:

Option A: Build a separate house for each family

• Very expensive! 🏗️
• Each house needs its own plumber, electrician, gardener
• Lots of wasted space

Option B: Build one big apartment building

• Everyone shares the building! 🏢
• One plumber, one electrician, one gardener for all
• Much cheaper and efficient!

Multi-tenancy is Option B!

Real Example

Think about Gmail:

• Millions of people use Gmail
• Google doesn’t build a separate email system for each person
• Everyone shares ONE Gmail system
• But you only see YOUR emails!

graph TD
    A["📧 Gmail System"] --> B["👤 Alice's Inbox]
    A --> C[👤 Bob's Inbox"]
    A --> D[👤 Carol's Inbox]
    A --> E["👤 Thousands More..."]

Why Companies Love Multi-Tenancy

🔒 Tenant Isolation: Keeping Everyone’s Stuff Safe

Here’s the tricky part: How do we share a building but keep everyone’s apartment private?

This is Tenant Isolation — making sure Tenant A can NEVER see Tenant B’s data!

The Key and Lock System

Remember apartment buildings have:

• One main entrance (shared)
• Individual apartment doors (private)
• Different keys for each apartment (isolation)

Cloud systems work the same way!

Three Ways to Isolate Tenants

Method 1: Separate Databases 🗄️🗄️🗄️

Each tenant gets their own filing cabinet.

Tenant A → Database A
Tenant B → Database B
Tenant C → Database C

✅ Most Secure — Complete separation ❌ Most Expensive — Many databases to manage

Method 2: Shared Database, Separate Tables 📊

One filing cabinet, but different drawers.

Shared Database
├── Table: TenantA_Users
├── Table: TenantA_Orders
├── Table: TenantB_Users
├── Table: TenantB_Orders

✅ Good Balance — Easier to manage ⚠️ Medium Risk — Must be careful with access

Method 3: Shared Everything with Tenant ID 🏷️

One drawer, but everything has name tags.

Users Table:
| id | tenant_id | name    |
|----|-----------|---------|
| 1  | A         | Alice   |
| 2  | B         | Bob     |
| 3  | A         | Alex    |

✅ Cheapest — Maximum sharing ⚠️ Careful Coding Needed — Always filter by tenant_id!

graph TD
    A["Tenant Isolation Methods"]
    A --> B["🗄️ Separate Databases"]
    A --> C["📊 Shared DB, Separate Tables"]
    A --> D["🏷️ Shared Tables with ID"]
    B --> E["Most Secure & Expensive"]
    C --> F["Balanced Approach"]
    D --> G["Most Efficient & Cheapest"]

⚖️ Shared vs Dedicated Resources

The big question every cloud architect asks:

“Should we SHARE this resource or give each tenant their OWN?”

The Pool Analogy 🏊

Imagine you run a resort:

What Gets Shared vs Dedicated?

Usually SHARED ✅

• Servers (the computers running everything)
• Network (the internet pipes)
• Basic Features (login, menus, buttons)
• Updates (everyone gets new features together)

Often DEDICATED 🔐

• Data Storage (for security)
• Processing Power (for big customers)
• Special Features (for premium tiers)
• Compliance Needs (banks, hospitals)

Real World Example: Spotify

When to Use Each?

graph TD
    A["Need to Decide: Share or Dedicate?"]
    A --> B{Is it sensitive data?}
    B -->|Yes| C["🔐 Dedicate It"]
    B -->|No| D{Does tenant need it?}
    D -->|High Performance| C
    D -->|Standard| E["✅ Share It"]

The Cost vs Security Balance

🎉 Putting It All Together

Let’s see how everything connects with a real example:

Shopify: A Multi-Tenant Masterpiece

Shopify hosts millions of online stores. Here’s how they use these concepts:

Three-Tier Architecture:

• 🎨 Presentation: Each store’s beautiful website
• 🧠 Application: Cart, checkout, inventory logic
• 💾 Data: Products, orders, customer info

Multi-Tenancy:

• One Shopify system runs ALL stores
• Store owners share the platform
• Each store has unique domain and design

Tenant Isolation:

• Your store’s orders are ONLY visible to you
• Customer data separated per store
• No store can peek at another’s sales

Shared vs Dedicated:

• ✅ SHARED: Shopify’s code, servers, CDN
• 🔐 DEDICATED: Each store’s data, themes, settings

🧠 Quick Summary

💡 Key Takeaway

Multi-tenant architecture is like running the world’s smartest apartment building:

• Build once, rent to many (efficient!)
• Give everyone their own key (secure!)
• Share the pool, private bedrooms (balanced!)

You now understand how Netflix, Gmail, Shopify, and thousands of other apps serve millions of users from one shared system! 🚀