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To keep one tenant from reading or changing another tenant’s rows, enforce tenant scope at the database boundary—not just in Go middleware. In a pooled PostgreSQL database, combine authenticated tenant selection, explicit propagation through the request, row-level security (RLS) policies, a restricted runtime role, and integration tests that exercise the real access path.
What must tenant isolation protect?
Every tenant-owned row needs an unambiguous tenant discriminator, such as a tenant_id. Every path that reads or writes those rows must preserve the boundary. A request context can carry the selected tenant, but it does not itself authorize access or prevent an unscoped query.
For application SQL, make tenant scope an explicit repository input and bind it as a query parameter; do not concatenate it into SQL. With pooled PostgreSQL tables, RLS adds a database-side enforcement point so a missed application predicate need not expose another tenant’s rows. The rule still depends on complete policy coverage and appropriately restricted credentials.
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Authenticate and authorize before creating tenant scope
First verify the user or session. Then determine which tenant that principal is allowed to act for. If a user may choose among several tenants, validate that selection before calling application services. A client-provided X-Tenant-ID header can express a selection, but it is not proof of membership.
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Carry the resolved scope explicitly
After authorization, attach the resolved tenant to the request context or pass it in a request-scoped service object. If using context.Value, use a private typed key rather than a plain string key, and fail closed when a required tenant is missing. Continue passing context.Context to I/O operations so cancellation and deadlines propagate as well. Go documents handlers and request contexts as mechanisms for composing request work and carrying values; neither is a database security boundary. See the Go net/http documentation and Go context documentation.
type tenantContextKey struct{}Conceptually, the HTTP chain should be: request, authentication, tenant membership or selection validation, tenant-scope creation, handler or service, then a tenant-scoped repository or RLS transaction. Keep tenant scope explicit for background jobs, command-line tasks, webhooks, tests, and internal service calls too; they may not pass through HTTP middleware.
How can PostgreSQL RLS enforce the row boundary?
Enable policies on tenant-bearing tables
Enable RLS on every table containing tenant data and define policies for the operations the application performs. PostgreSQL 18 explains that policies determine which rows ordinary queries can return or modify; with RLS enabled and no applicable policy, access defaults to deny. Its documentation states: “If no policy exists for the table, a default-deny policy is used, meaning that no rows are visible or can be modified.” Read the PostgreSQL 18 row security documentation for policy behavior and caveats.
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A policy can compare each row’s tenant discriminator with a PostgreSQL setting established for the current database operation. For a table whose tenant_id and runtime tenant setting are UUIDs, an illustrative policy is:
ALTER TABLE invoices ENABLE ROW LEVEL SECURITY;
CREATE POLICY invoice_tenant_scope ON invoices
USING (tenant_id = current_setting('app.tenant_id', true)::uuid)
WITH CHECK (tenant_id = current_setting('app.tenant_id', true)::uuid);Adapt the setting name and types to the schema. In this example, USING restricts which existing rows can be selected, updated, or deleted; WITH CHECK constrains proposed row values, including inserted rows and updated rows. When no setting exists, the comparison does not match a tenant row, so access is denied by the policy. A malformed value or incompatible type can instead cause an error, which should not be converted into an unscoped fallback.
Set tenant state on the same transaction as the query
Set the runtime tenant setting on the same connection and transaction that runs the protected SQL. A transaction-local setting, such as PostgreSQL’s set_config with its local flag enabled, avoids leaving tenant state on a pooled connection after the transaction ends. In Go, begin a transaction, set the tenant value through that transaction, run the repository queries through that same transaction, then commit or roll back. Do not set a session-level value and assume a pooled connection will be discarded after one request.
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Confirm the transaction-local configuration behavior with the documentation for the database driver and transaction path you actually use. The Go database API choice does not change the key rule: configuration and protected queries must share the correct transaction and connection. AWS also recommends runtime tenant context and RLS for pooled PostgreSQL; see its row-level security recommendations.
Keep the runtime database role out of the bypass paths
The application’s runtime role should not own tenant tables and should not have superuser or BYPASSRLS privileges. PostgreSQL documents that superusers and BYPASSRLS roles always bypass RLS, and table owners normally bypass it too. ALTER TABLE ... FORCE ROW LEVEL SECURITY makes the owner subject to policies, but it does not remove the bypass privileges of superusers or BYPASSRLS roles. Keep privileged maintenance in a separate, explicit path.
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RLS is not a rule for every database operation: PostgreSQL notes that whole-table operations such as TRUNCATE and REFERENCES are not subject to row security. Review those operations, as well as views, functions, joins, bulk work, migrations, and administrative access, as part of the isolation design.
How can an integration test demonstrate the boundary?
Run the test against PostgreSQL and use the same class of restricted role as the application, not a table owner, superuser, or role with BYPASSRLS. Seed known rows for tenants A and B, then exercise the production-shaped request-to-repository or transaction path. Check both what the caller can see and what it can change.
- Under tenant A scope, read A’s row successfully and confirm B’s row is unavailable.
- Try updating and deleting B’s row; verify that no unauthorized change occurs. Also verify an allowed change to A’s row.
- Try inserting a row with tenant B’s discriminator while scoped as A; it must be rejected or must not become a B-owned row.
- Try changing an A row’s tenant discriminator to B and verify that the policy prevents reassignment.
- Run an operation without tenant context and with a malformed or unauthorized tenant selection; confirm the application fails closed.
- Reuse pooled connections across A, B, and missing-context operations to check that tenant state does not leak between requests.
These checks demonstrate the behavior of the tested schema, policies, role, and code paths; they do not prove that every query in a larger application is covered. Add repository audits or broader endpoint tests when the scope requires them. PostgreSQL’s documentation shows why checking writes matters: RLS can filter visible rows and can also affect which rows an update modifies.
When is pooled row-level tenancy the right fit?
A shared table with a tenant column and RLS is one tenancy pattern, not a universal best choice. Other patterns include a schema per tenant or a database per tenant. Compare them against your isolation boundary and blast radius, operational work for provisioning and migrations, backup and tenant-lifecycle needs, resource allocation, administrative access, and the failure modes your team can manage.
Shared tables make policy completeness, privileged credentials, and connection-state handling central concerns. Separate schemas or databases change the boundary and operational burden, but no single model is best for every application. There is no defensible universal scale threshold or cost comparison established here; choose based on your requirements and validate the operational trade-offs for your system.
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