Multi-Tenancy
Treat tenant identity as an authorization boundary, not a query convenience.
Choose an isolation model
- Database per tenant: strongest isolation and highest operational cost.
- Schema per tenant: strong logical isolation with shared infrastructure.
- Shared schema with
tenant_id: simplest operations, but every access path must enforce scope. - Document the selected model and prohibit repositories from bypassing it.
Resolve tenant identity
- Derive the tenant from a verified token claim, trusted host mapping, or authenticated API key.
- Reject missing, unknown, disabled, or conflicting tenant identifiers.
- Never trust a public
X-Tenant-Idheader by itself. - Clear servlet thread-local context in
finally; use ReactorContextfor reactive flows.
Enforce isolation
- Apply tenant selection before opening the persistence session or transaction.
- Include tenant identity in unique constraints, cache keys, idempotency keys, and object storage paths.
- Prevent cross-tenant joins and unrestricted administrative repositories.
- Authorize support impersonation explicitly and audit every use.
Operations
- Run migrations per database/schema with resumable progress and version reporting.
- Propagate tenant identity into scheduled jobs, messages, and async tasks explicitly.
- Limit noisy tenants with quotas and per-tenant observability using bounded identifiers.
- Test negative cross-tenant access, not only successful tenant queries.
Examples
- See
examples/good-tenant-filter.javaandexamples/bad-tenant-filter.java.
Gotchas
- Agent trusts a tenant header supplied by the caller - derive tenant from authenticated context.
- Agent forgets to clear a servlet
ThreadLocal- pooled threads can leak one tenant into another request. - Agent scopes database queries but not cache keys - cached data can cross tenants.
- Agent starts a transaction before selecting the tenant - routing may choose the wrong database.
- Agent runs background jobs without tenant context - make tenant an explicit job parameter.