DEV Community: Rahul Bhatt

⚡️ Building a Multi-Tenant Spring Boot Starter from Scratch — with Subdomain Routing, Dynamic Datasources & Ego Logs

Rahul Bhatt — Sat, 28 Jun 2025 17:55:15 +0000

🚀 Building a Multi-Tenant Spring Boot Starter from Scratch

Developer Preview v0.1.0-SNAPSHOT is live!

🧠 Why This Starter Exists

Spring Boot lacks a true plug-and-play solution for multi-tenant SaaS platforms. Most solutions are deeply coupled, opinionated, or too abstract.

But also — this project came from a personal place.

Right after I received a disappointing 0.5 LPA raise (yes, backwards momentum), I decided to convert that frustration into engineering fire. Inspired by Blue Lock, I wanted to log every technical decision like a striker chasing goals — enter the ego-logs/ folder.

🧱 Project Structure

├── starter/       → Core Spring Boot auto-config starter
├── demo/          → Sample app showing real usage
├── ego-logs/      → My engineering journal (yes, Blue Lock–style)
├── scripts/       → Placeholder for CI or future tools
├── daily/         → Temp debug + local artifacts

🧩 Features in Developer Preview

✅ Subdomain-based tenant resolution
✅ Header-based tenant resolution
✅ Tenant registry (in-memory)
✅ Per-DB isolation strategy
✅ @EnableTenantIsolation annotation
✅ Clean Spring Boot auto-configuration
⚙️ Extensible resolvers + datasource logic

📦 Add It via JitPack

Maven

<dependency>
  <groupId>com.github.rahul-s-bhatt</groupId>
  <artifactId>multi-tenant-springboot-starter</artifactId>
  <version>v0.1.0-SNAPSHOT</version>
</dependency>

Gradle

dependencies {
  implementation("com.github.rahul-s-bhatt:multi-tenant-springboot-starter:v0.1.0-SNAPSHOT")
}

💻 Usage Snapshot

Enable the starter via `application.yml`

multi-tenancy:
  default-tenant-id: acme
  registry:
    type: IN_MEMORY
    in-memory-tenants:
      - tenantId: acme
        datasourceUrl: jdbc:h2:mem:acme
        username: sa
      - tenantId: globex
        datasourceUrl: jdbc:h2:mem:globex
        username: sa
  isolation:
    type: TENANT_PER_DATABASE
  resolution:
    type: HTTP_HEADER

🧠 How It Works

flowchart TD
  A[Request] --> B[Filter: TenantResolver]
  B --> C[TenantContextHolder]
  C --> D[TenantRegistry]
  D --> E[RoutingDataSource]
  E --> F[DB A or DB B]

🔥 About `ego-logs/`

This is my commitment to daily logging of what I learned, attempted, failed at, or broke. No GitHub green dots — real dev logs.

Just like Blue Lock's Ego Jinpachi believes in personal records to dominate the game, these ego logs are my engineering training arcs.

🛣️ What's Coming

JWT-based tenant resolution
Schema-based isolation
Runtime tenant onboarding APIs
Liquibase / Flyway integration
Multi-tenant Spring Security support

🧑‍💻 Contribute or Fork

If you're working on a SaaS platform, this is for you.
Star 🌟 the repo, fork it, build your own isolation strategy.

GitHub → rahul-s-bhatt/multi-tenant-springboot-starter
JitPack → jitpack.io/#rahul-s-bhatt

🫡 Final Words

Dev discipline isn't just commits — it's clarity, context, and ego-fueled progress.

This is just the beginning.

If you enjoyed this drop, follow @rahul_s_bhatt for future dev logs, open-source updates, and architecture deep dives.

Day 3 : DX-First Thinking: Why I Added @EnableTenantIsolation to My Spring Boot Starter

Rahul Bhatt — Mon, 23 Jun 2025 18:14:58 +0000

DX-First Thinking: Why I Added `@EnableTenantIsolation` to My Spring Boot Starter

Day 3 of building multi-tenant-springboot-starter was less about code, more about mindset.

I wanted developers to switch between DATABASE, SCHEMA, and SHARED isolation strategies for tenants. The default Spring Boot way would be
application.yml:

tenant:
  strategy: DATABASE

That works, but I asked myself:

“What would it look like if Spring had built this?”

So I created:

@EnableTenantIsolation(strategy = TenantIsolationStrategy.SCHEMA)

💡 This annotation uses ImportBeanDefinitionRegistrar and EnvironmentAware to inject the tenant.strategy key into the Spring Environment — before anything binds.

What I learned:
Boot auto-config works great, but it doesn't understand your custom annotations — unless you bridge them using @import(...)

The BEAN_CONTAINER trick in JPA is mandatory when manually wiring multiple EntityManagerFactoryBeans — without it, entity scanning breaks

Key Takeaway:
Framework-level DX is about thinking like Spring, not just using it.

Tomorrow: schema-per-tenant Hibernate integration.

Repo: github.com/rahul-s-bhatt/multi-tenant-springboot-starter

Follow for more build-in-public logs ✨

Day 1 of My Spring Boot Multitenancy Starter: Contexts, Filters, and Auto-Config

Rahul Bhatt — Sun, 22 Jun 2025 10:25:14 +0000

Day 1 of My Spring Boot Multitenancy Starter: Contexts, Filters, and Auto-Config

After Day 0’s emotional ignition, Day 1 was about structure, clarity, and hands-on bootstrapping.

🎯 Goal

Scaffold the foundational skeleton of a plug-and-play Spring Boot multitenancy starter — just like how Spring Boot itself feels.

🧱 What I Built Today

🧠 Core Concepts Implemented

Thread-safe TenantContextHolder using ThreadLocal
Pluggable TenantResolver interface (subdomain strategy default)
TenantFilter to set/clear context per request
TenantDefinition (record) to hold metadata like tenantId, creds, etc.
TenantRegistry + InMemoryTenantRegistry to register and fetch tenants
TenantRoutingDataSource to delegate dynamically
DataSourceFactory to build isolated HikariDataSources per tenant
Custom YAML props via HikariTenantPoolProperties
Spring Boot AutoConfig:
- MultitenancyAutoConfiguration
- TenantRegistryAutoConfig
- TenantDataSourceAutoConfig
@EnableMultitenancy annotation to wire everything

🧪 Tests Added

✅ TenantContextTest — validate isolation
✅ TenantContextLeakTest — simulate misuse
✅ TenantContextConcurrencyTest — 100-thread stress test

🧠 What I Learned Today

🔹 Java Concurrency

Built a cheat-sheet on:

ThreadLocal
ExecutorService, CountDownLatch, AtomicBoolean

🔹 Maven Structuring

Local publish using mvn install
Clean starter module structure
IDE tricks for IntelliJ Maven + .iml

🔹 Spring Boot Internals

@ImportAutoConfiguration flow
AutoConfiguration.imports mechanism
Clean starter design, Spring-style

📁 Folder Structure

multi-tenant-springboot-starter/
├── pom.xml
├── starter/
│ ├── pom.xml
│ └── src/main/java/org/nirvikalpa/...
│ └── src/test/java/org/nirvikalpa/...
├── demo/ # coming tomorrow

🧭 Next Steps (Day 2 Plan)

Build a tenant onboarding workflow
Wire demo app to consume the starter
Expose /health per-tenant endpoint
Reflect in Ego Log #002

🔗 Repo: github link

Thanks for following my journey.

This is more than code — it's my architectural diary.

I Got a 0.5% Raise. So I’m Building a Multitenancy Starter for Spring Boot.

Rahul Bhatt — Sat, 21 Jun 2025 17:32:21 +0000

I Got a 0.5% Raise. So I’m Building a Multitenancy Starter for Spring Boot.

After spending weekends and late nights scaling a multi-tenant SaaS in FinTech, I received a 0.5% raise.

It said more than words ever could.

But instead of burning out or shutting down, I decided to build in public the very thing I wish existed:

A true Spring Boot Multitenancy Starter — built with clarity, built with pain, built with purpose.

🧱 What I'm Building

I don't want to make another wrapper or a copy-paste blog pattern.

I’m building:

🧠 A thread-safe TenantContextHolder
🔌 Database-per-tenant routing
⚙️ Pluggable resolver strategies
🧰 Runtime onboarding hooks
🩺 Tenant-aware health indicators & logs
✨ Auto-configured like Spring Boot itself

Think: spring-boot-starter-data-jpa — but for multitenancy.

🧠 Day 0: The Ego Kick

It didn’t start with a plan. It started with rage.

I opened ChatGPT and typed:

“If Spring Boot had to build multitenancy the right way — how would it design it?”

Then I fell down the rabbit hole of spring-boot-autoconfigure, conditionals, DataSourceBuilder, and bean registration logic.

I wasn’t looking for a tutorial. I was looking for intent. Design intent. Spring’s kind of intent.

And slowly, the fog started clearing.

🗂️ What I Scaffolded on Day 0

Here’s the first shape:

org.nirvikalpa.multitenancy
├── context/ # Holds TenantContextHolder (ThreadLocal)
├── resolver/ # JWT / Subdomain / Header strategies
├── datasource/ # RoutingDataSource logic
├── config/ # Auto-config magic
└── starter/ # What end users depend on

🔮 Why I’m Building in Public

🧭 It keeps me honest and aligned
💬 Feedback can shape design before it ossifies
🪞 You see not just the final code, but the internal war that built it

This isn’t just about multitenancy. It’s about building with intent instead of reaction.

🔗 GitHub (Day 0 State)

👉 github.com/rahulsb/spring-boot-starter-multitenancy

(still raw, still real — but it's up)

📅 What’s Next?

Finalize the pluggable TenantResolver interface
Decide if we default to JWT or subdomain
Log Ego Entry #002
Publish a Twitter/X launch thread

If you've ever struggled with multitenant systems in Java or wished for a true starter — follow this build. I’m designing in the open, thinking loud, and logging everything.

Thanks for reading my Day 0.

I built this out of fire. Hope it helps light someone else's path.

DEV Community: Rahul Bhatt

⚡️ Building a Multi-Tenant Spring Boot Starter from Scratch — with Subdomain Routing, Dynamic Datasources & Ego Logs

🚀 Building a Multi-Tenant Spring Boot Starter from Scratch

🧠 Why This Starter Exists

🧱 Project Structure

🧩 Features in Developer Preview

📦 Add It via JitPack

Maven

Gradle

💻 Usage Snapshot

Enable the starter via application.yml

🧠 How It Works

🔥 About ego-logs/

🛣️ What's Coming

🧑‍💻 Contribute or Fork

🫡 Final Words

Day 3 : DX-First Thinking: Why I Added @EnableTenantIsolation to My Spring Boot Starter

DX-First Thinking: Why I Added @EnableTenantIsolation to My Spring Boot Starter

Day 1 of My Spring Boot Multitenancy Starter: Contexts, Filters, and Auto-Config

Day 1 of My Spring Boot Multitenancy Starter: Contexts, Filters, and Auto-Config

🎯 Goal

🧱 What I Built Today

🧠 Core Concepts Implemented

🧪 Tests Added

🧠 What I Learned Today

🔹 Java Concurrency

🔹 Maven Structuring

🔹 Spring Boot Internals

📁 Folder Structure

🧭 Next Steps (Day 2 Plan)

I Got a 0.5% Raise. So I’m Building a Multitenancy Starter for Spring Boot.

I Got a 0.5% Raise. So I’m Building a Multitenancy Starter for Spring Boot.

🧱 What I'm Building

🧠 Day 0: The Ego Kick

🗂️ What I Scaffolded on Day 0

🔮 Why I’m Building in Public

🔗 GitHub (Day 0 State)

📅 What’s Next?

Enable the starter via `application.yml`

🔥 About `ego-logs/`

DX-First Thinking: Why I Added `@EnableTenantIsolation` to My Spring Boot Starter