Multi-tenancy patterns in Firebase - Commands & Configuration

Introduction

Multi-tenancy means sharing one app or database for many users or groups, called tenants. It helps save money and makes managing many users easier by keeping their data separate but using the same system.

When you build a SaaS app that serves many companies but wants to keep their data private.

When you want to save costs by using one Firebase project for multiple user groups.

When you want to manage user access and data isolation easily in one place.

When you want to scale your app without creating many separate Firebase projects.

When you want to customize features or data views for different user groups.

Config File - firestore.rules

firestore.rules

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    // Each tenant has its own collection
    match /tenants/{tenantId}/{document=**} {
      allow read, write: if request.auth != null && request.auth.token.tenantId == tenantId;
    }
  }
}

This Firestore security rule ensures data isolation by allowing users to access only their tenant's data. The tenantId in the path matches the tenant claim in the user's authentication token. This way, users from one tenant cannot read or write data from another tenant.

Commands

Deploys the Firestore security rules to enforce tenant data isolation.

Terminal

firebase deploy --only firestore:rules

Expected Output

=== Deploying to 'my-firebase-project'...



i  deploying firestore.rules

✔  firestore.rules: Rules deployed successfully



✔  Deploy complete!

→

--only firestore:rules - Deploy only Firestore security rules without affecting other services

Imports users with tenant information in their custom claims to Firebase Authentication.

Terminal

firebase auth:import users.json --hash-algo=SCRYPT --rounds=8 --mem-cost=14

Expected Output

✔ Imported 3 users successfully.

→

--hash-algo=SCRYPT - Specifies the password hashing algorithm used for imported users

Sets a configuration value for tenant ID to use in Firebase Functions for tenant-specific logic.

Terminal

firebase functions:config:set tenant.id="tenant123"

Expected Output

✔  Functions config updated.

Deploys Firebase Functions that can use tenant config and enforce tenant-specific behavior.

Terminal

firebase functions:deploy

Expected Output

=== Deploying to 'my-firebase-project'...



i  deploying functions

✔  functions: Finished running predeploy script.

✔  functions: functions deployed successfully



✔  Deploy complete!

Key Concept

If you remember nothing else from this pattern, remember: keep each tenant's data separate by using security rules that check tenant identity in user tokens.

Common Mistakes

Not setting tenant info in user authentication tokens.

Without tenant info, security rules cannot restrict data access properly, risking data leaks.

Always assign tenant IDs as custom claims in user tokens during authentication or user import.

Writing security rules that do not check tenant ID in the document path.

This allows users to access data from other tenants, breaking data isolation.

Structure your Firestore data with tenant IDs in the path and enforce tenant ID checks in rules.

Deploying functions or rules without testing tenant access.

Errors in rules or functions can cause unexpected access or failures.

Test tenant-specific access with different user accounts before deploying to production.

Summary

Use Firestore security rules to isolate tenant data by checking tenant IDs in user tokens.

Deploy rules and functions with tenant-aware logic to enforce data separation and custom behavior.

Import users with tenant info in authentication tokens to enable secure multi-tenancy.

Practice

1. What is the main purpose of multi-tenancy in Firebase applications?

easy

A. To allow multiple users to share the same app while keeping their data separate

B. To increase the speed of database queries

C. To reduce the cost of Firebase hosting

D. To enable offline data access for users

Solution

1. Step 1: Understand multi-tenancy concept

   Multi-tenancy means many users use one app but their data stays separate.

2. Step 2: Identify the purpose in Firebase context

   Firebase apps use multi-tenancy to keep user data isolated while sharing the app.

3. Final Answer:

   To allow multiple users to share the same app while keeping their data separate -> Option A

4. Quick Check:

   Multi-tenancy = separate data for shared app [OK]

Hint: Multi-tenancy means shared app, separate data [OK]

Common Mistakes:

• Confusing multi-tenancy with performance optimization
• Thinking multi-tenancy is about offline access
• Assuming multi-tenancy reduces hosting costs

2. Which Firestore data structure is best for separating tenant data in a multi-tenant Firebase app?

easy

A. A single collection with tenant ID as a field in each document

B. Separate collections for each tenant grouped by tenant ID

C. One document per tenant with all data nested inside

D. Storing all tenant data in one document without tenant ID

Solution

1. Step 1: Review Firestore data organization

   Firestore uses collections and documents to organize data.

2. Step 2: Choose best pattern for tenant separation

   Grouping data by tenant ID in separate collections keeps tenant data isolated and easier to secure.

3. Final Answer:

   Separate collections for each tenant grouped by tenant ID -> Option B

4. Quick Check:

   Tenant data separated by collections = Separate collections for each tenant grouped by tenant ID [OK]

Hint: Use collections grouped by tenant ID for clear separation [OK]

Common Mistakes:

• Putting all tenant data in one document
• Not using tenant ID to separate data
• Using a single collection without grouping

3. Given this Firestore security rule snippet for multi-tenancy:

match /tenants/{tenantId}/data/{docId} {
  allow read, write: if request.auth.token.tenant == tenantId;
}

What happens if a user with tenant ID 'tenantA' tries to read data from 'tenantB'?

medium

A. Access is granted because tenant IDs are ignored

B. Access is granted only for read but not write

C. Access is denied only if the document does not exist

D. Access is denied because tenant IDs do not match

Solution

1. Step 1: Understand the security rule condition

   The rule allows access only if the user's tenant ID matches the tenantId in the path.

2. Step 2: Apply the condition to the user and requested tenant

   User's tenant ID is 'tenantA' but tries to access 'tenantB' data, so condition fails.

3. Final Answer:

   Access is denied because tenant IDs do not match -> Option D

4. Quick Check:

   Tenant ID mismatch blocks access [OK]

Hint: Tenant ID in token must match path tenant ID [OK]

Common Mistakes:

• Assuming access is granted without tenant ID check
• Thinking read access is allowed but write is denied
• Ignoring tenant ID in security rules

4. You wrote this Firestore rule for multi-tenancy:

match /tenants/{tenantId}/data/{docId} {
  allow read, write: if request.auth.token.tenantId == tenantId;
}

But users report access errors. What is the likely problem?

medium

A. The token field name is incorrect; it should be 'tenant' not 'tenantId'

B. The path variable 'tenantId' is not defined in the rule

C. Firestore does not support tenant-based security rules

D. The rule allows access to all tenants without restriction

Solution

1. Step 1: Check token field name in the rule

   The rule uses 'request.auth.token.tenantId' but the token field is usually 'tenant'.

2. Step 2: Understand impact of wrong token field

   If the token field name is wrong, the condition always fails, causing access errors.

3. Final Answer:

   The token field name is incorrect; it should be 'tenant' not 'tenantId' -> Option A

4. Quick Check:

   Correct token field name fixes access [OK]

Hint: Match token field name exactly in rules [OK]

Common Mistakes:

• Using wrong token field name
• Assuming Firestore ignores token field names
• Not defining path variables correctly

5. You want to design a Firebase app supporting multiple tenants with isolated data and secure access. Which combination of patterns is best?

hard

A. Use a single Firestore collection for all tenants and filter data in the app code

B. Use Firebase Realtime Database instead of Firestore for multi-tenancy

C. Create separate Firestore collections per tenant and enforce tenant ID checks in security rules

D. Store all tenant data in one document and use client-side filtering for access control

Solution

1. Step 1: Evaluate data separation methods

   Separate collections per tenant keep data isolated and easier to manage.

2. Step 2: Apply security best practices

   Security rules must check tenant ID to prevent unauthorized access.

3. Step 3: Compare options

   Create separate Firestore collections per tenant and enforce tenant ID checks in security rules combines data separation and security rules, ensuring isolation and protection.

4. Final Answer:

   Create separate Firestore collections per tenant and enforce tenant ID checks in security rules -> Option C

5. Quick Check:

   Separate collections + security rules = best multi-tenancy [OK]

Hint: Combine data separation with security rules for best isolation [OK]

Common Mistakes:

• Relying on client-side filtering only
• Using single collection without security rules
• Choosing Realtime Database without need