Why it is worth attention

It offers a complete, production-ready multi-tenancy solution for .NET 10, including tenant-aware JWT, three-layer cache, and per-tenant circuit breaker, with a documented design rationale and a verified end-to-end flow.

Who it is for

.NET developers building multi-tenant SaaS applications
Architects designing tenant isolation strategies
DevOps engineers managing per-tenant database deployments
Teams requiring plan-based feature toggles and usage quotas

Use cases

Building a multi-tenant SaaS backend with isolated databases per tenant
Dynamically resolving and caching tenant-specific database connections
Running tenant database migrations with per-tenant failure isolation
Implementing plan-based feature flags and rate limits

Strengths

Complete solution with a detailed design document (SDD.md)
Verified end-to-end flow with step-by-step instructions (cold start) and all tests passing (11 unit, 39 integration)
Includes per-tenant resilience with configurable timeout and circuit breaker patterns
Provides a migration tool that isolates failures per tenant and supports dry-run preview

Considerations

Containerized API cannot use the seeded demo tenants because DbHost is hardcoded to 'localhost' (only works when running on host with Docker's published ports)
Automatic testing of the circuit breaker and /health/tenants circuit state is not yet implemented
EF Core 10 does not wrap a tenant's full migration batch in a transaction, so partial-batch failures require manual schema inspection

README quick start

SaaS Multi-Tenant Isolation Engine

A Database-per-Tenant multi-tenancy building block for .NET 10: dynamic per-tenant connection resolution, JWT authentication with tenant-claim cross-checking, a three-layer tenant metadata cache, plan-based feature flags/quotas, per-tenant resilience (timeout + circuit breaker), and a migration tool with per-tenant failure isolation.

See docs/SDD.md for the full design rationale.

Solution layout

src/BuildingBlocks/BuildingBlocks.MultiTenancy/   Reusable multi-tenancy plumbing (no DB dependency)
src/Services/Catalog.Admin/                       Central catalog: Plan/Tenant/PlanFeature/PlanQuota + EF store
src/Services/SaaS.CoreEngine.Api/                 The tenant-facing API (billing domain demo: Customer/Product/Invoice)
src/Tools/Tools.DbMigrator/                        Sweeps active tenants and applies pending migrations
tests/BuildingBlocks.MultiTenancy.UnitTests/       Pure unit tests, no Docker required
tests/SaaS.CoreEngine.IntegrationTests/            Testcontainers-backed integration tests (require Docker)
docker/postgres-tenants/init/                      First-boot script creating the demo tenant databases
docker-compose.yml                                 Local dev stack: postgres-central, postgres-tenants, redis, api

Prerequisites

.NET SDK 10.0+
Docker Desktop (for docker compose and for the Testcontainers-backed integration tests)
dotnet-ef global tool (dotnet tool install --global dotnet-ef), matching the EF Core version pinned in Directory.Packages.props

Cold start (verified flow)

This is the exact sequence that was run and verified end-to-end for this repository. It runs the API and Tools.DbMigrator on the host via dotnet run, with Postgres and Redis provided by docker-compose — not the containerized api service (see "Known limitation" below).

# 1. Copy the environment template (edit if you need non-default ports/credentials)
Copy-Item .env.example .env

# 2. Start Postgres (catalog + tenants cluster) and Redis
docker compose up -d postgres-central postgres-tenants redis

# 3. Wait for all three to report healthy
docker compose ps

# 4. Apply the catalog migration
$env:DOTNET_CATALOG_CONNECTION = "Host=localhost;Port=5433;Database=saas_catalog;Username=postgres;Password=postgres"
dotnet ef database update --project src/Se

Description

Database-per-Tenant multi-tenancy engine for .NET 10 — dynamic per-tenant connection resolution, JWT auth with tenant-claim cross-checking, plan-based feature flags/quotas, per-tenant resilience (circuit breaker + bulkhead), and a zero-downtime migration tool.

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