ENTRY 02 / 05FULL-STACK2026TYPE: INTERNAL BUILD

Atlas

A multi-tenant SaaS core — auth, billing, tenancy — built once, hardened, and reused on every product since.

STACK — Next.js · TypeScript · PostgreSQL · Prisma · Stripe · Redis

FIG. 02.0 — SYSTEM COMPOSITION, DRAWN IN CODE

SEC. 01BRIEF

THE PROBLEM, PLAINLY

Every SaaS project begins with the same six weeks: authentication, organizations, roles, billing, emails, background jobs. Atlas was built to make those six weeks a checkbox — a production-grade core we harden continuously and fork per product.

The discipline was to build it like it already had paying tenants: rate limits, row-level tenancy checks in one place, idempotent webhooks, and load numbers measured rather than assumed.

SEC. 02APPROACHDECISIONS, NOT FEATURES

Tenancy as a single choke point

Every query passes a tenant resolver — one module owns isolation, so a leak requires beating one review, not thirty. Postgres row-level security backs it up at the database.

Billing that survives retries

Stripe webhooks are idempotent and event-sourced: every billing state transition replays cleanly, and a dropped webhook heals on the next sync pass.

Server components by default

Pages render on the server; interactivity ships as islands. First Load JS stays under 100 kB on every route — measured in CI, failed if exceeded.

Load-tested before launch-tested

k6 smoke and soak runs are part of the pipeline. The p95 number on this page comes from the soak report, not from a quiet afternoon.

SEC. 03ARCHITECTURETHE DIAGRAM IS THE CONTRACT

FIG. — Edge cache in front of Next.js SSR, one API layer with a tenant resolver choke point, Postgres + Redis behind it, Stripe at arm’s length.

SEC. 04ARTIFACTSPROOF, NOT PROMISES

>_ BUILD + SOAK

$ next build
Route (app)                    Size     First Load JS
┌ ○ /                          4.1 kB   93 kB
├ ○ /dashboard                 8.7 kB   99 kB
├ ƒ /api/v1/*                  —        —
└ ○ /settings/billing          6.2 kB   97 kB
 
$ k6 run soak.js --vus 200 --duration 30m
http_req_duration  p50=61ms  p95=182ms  p99=290ms
http_req_failed    0.00%
checks             100.00%  (18,442 passed)

§ TENANCY MODES

Pooled: Shared schema, RLS-enforced — default for small tenants
Siloed schema: Per-tenant schema for regulated data
Read replica: Analytics traffic isolated from the primary
Session model: HttpOnly, rotating, device-scoped revocation

ENGINEERING NOTE

The core insight is negative space: Atlas is defined by what product teams never have to think about again. Every hour it absorbs is an hour a product bet gets back.

SEC. 05OUTCOMEMEASURED, NOT ESTIMATED

0ms

P95 UNDER 200-VUS SOAK

LIGHTHOUSE PERFORMANCE

0kB

FIRST-LOAD JS CEILING, ENFORCED IN CI

CROSS-TENANT READS IN AUDIT

NEXT ON THE LEDGER — ENTRY 03 / 05This Site →