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Building a SaaS Application in Python — Complete Roadmap

From JOHNWICK

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1 — Vision & MVP Goal: ship a minimal, usable product that solves one real problem and can onboard paying users. MVP features (example):

  • User signup / login / email verification
  • Subscription & payments (Stripe)
  • Multi-tenant data separation (tenant per customer)
  • Core product functionality (e.g., dashboard + CRUD resources)
  • Billing page + plan management
  • Admin dashboard (users, billing, usage)
  • Basic monitoring & error tracking


2 — High-level architecture

  • Clients: Web SPA (React/Vue/Next) + optional mobile
  • API: Python backend (FastAPI or Django REST Framework)
  • DB: PostgreSQL (primary relational store)
  • Cache: Redis (session, rate limiting, background job queue with RQ/Celery)
  • Storage: S3-compatible object store for user files
  • Payments: Stripe (subscriptions + webhooks)
  • Auth: JWT or session cookies; use OAuth 2.0 flows if needed
  • Deployment: Docker images → Kubernetes or managed containers (ECS, Cloud Run)
  • CI/CD: GitHub Actions / GitLab CI to build, test, deploy
  • Observability: Sentry (errors), Prometheus + Grafana (metrics), logs to ELK / Cloud logging


3 — Recommended tech stack (production-ready)

  • Backend framework:
  • FastAPI — modern, async, excellent performance, auto OpenAPI docs.
  • or Django + Django REST Framework — batteries-included, admin UI, ORM features.
  • ORM: SQLAlchemy (FastAPI) or Django ORM
  • Auth & Users: fastapi-users or custom with passlib/bcrypt; social logins optional
  • Payments: Stripe SDK (webhooks)
  • Background jobs: Celery (with Redis or RabbitMQ) or RQ for simpler workloads
  • Database: PostgreSQL (use managed RDS / CloudSQL)
  • Cache / sessions: Redis
  • Object Storage: AWS S3 (or DigitalOcean Spaces)
  • Containerization: Docker
  • Kubernetes: k8s if you need autoscaling; otherwise use managed services (Cloud Run, ECS, Heroku)
  • CI/CD: GitHub Actions
  • Monitoring & Errors: Sentry (errors), Prometheus/Grafana or cloud metrics
  • Testing: pytest, factory-boy, pytest-cov
  • Linting & formatting: flake8/ruff, black, isort
  • Secrets management: Vault, AWS Secrets Manager, or env vars via a secret store


4 — Data model & tenancy strategies Tenancy options:

  • Shared schema (tenant_id on each row) — simplest; good for many SaaS apps.
  • Schema per tenant — more isolation; more complex migrations.
  • Database per tenant — best isolation but operationally heavy.

Start with: shared schema + tenant_id + row level security if needed (Postgres RLS). Core models: User, Organization (tenant), Subscription, Invoice, Resource (your domain model), AuditLog.


5 — Security essentials

  • Always store passwords hashed with bcrypt/argon2 (use libraries).
  • Use HTTPS everywhere (TLS).
  • Validate & sanitize input; use parameterized DB queries (ORM does this).
  • Protect against CSRF if using cookies.
  • Rate limit login endpoints; implement account lockout/throttling.
  • Secure webhooks (verify Stripe signature).
  • Secrets in secure store; never commit .env.
  • Use CSP, secure headers (Helmet-like middleware).
  • Use 2FA for admin accounts.


6 — Payments & billing

  • Use Stripe for subscriptions: products, prices, trials, coupons.

Implement Stripe webhooks: invoice.payment_succeede invoice.payment_failed, customer.subscription.updated.

  • Keep records of subscription status in your DB; reconcile via webhooks + periodic polling.
  • Offer free trial flows: mark status, set trial end behavior.
  • Handle failed payments: retries, email notifications, temporary read-only mode.


7 — Development milestones (agile sprint plan) Sprint 0 (planning)

  • Define product flows, wireframes, API contracts (OpenAPI), data model.
  • Create repo, CI pipeline scaffold, dev environment instructions.

Sprint 1 (Core Auth & Tenant)

  • User registration, login, email verification
  • Organization (tenant) creation and isolation
  • JWT or session auth implemented
  • Basic UI pages (login, signup, dashboard skeleton)

Sprint 2 (Core Product)

  • Implement main product CRUD & business logic
  • Add tests for core flow
  • Add role-based access (admin, user)

Sprint 3 (Billing + Subscription)

  • Integrate Stripe checkout or billing portal
  • Implement webhooks, subscription state, billing UI

Sprint 4 (Background Jobs & Storage)

  • Add file uploads to S3
  • Background tasks (email sending, heavy processing)

Sprint 5 (Admin + Monitoring)

  • Admin dashboard: manage users, billing, usage
  • Setup Sentry, metrics, logs

Sprint 6 (Scaling & Harden)

  • Load testing, caching, query optimization, DB indexing
  • Containerize, add k8s deployment & CI/CD production pipeline

Sprint 7 (Polish & Launch)

  • UX fixes, analytics, privacy & GDPR compliance, docs, Onboarding emails
  • Pilot with beta users


8 — CI/CD & testing strategy

  • Local: pre-commit hooks (black, isort, ruff), run unit tests, linters.
  • CI (on push / PR): run tests, static analysis, build Docker image, push to registry on main.
  • CD: Deploy to staging automatically; production on merge to release/main with manual approval.
  • Tests: unit, integrationDB), e2e (playwright or Cypress for UI), contract tests for webhooks/APIs.
  • Schema migrations: use Alembic (SQLAlchemy) or Django migrations; apply in deployment pipeline.


9 — Observability & reliability

  • Errors: Sentry with environment tags (staging/prod).
  • Metrics: expose Prometheus metrics from backend; dashboard in Grafana.
  • Logging: structured logs (JSON) shipped to ELK or cloud logging.
  • Health checks: /healthz, liveness/readiness for orchestration.
  • Backups: automated DB backups + test restore procedures.
  • SLA planning: define RTO/RPO goals.


10 — UX, onboarding & growth features

  • Easy signup + clear onboarding flows
  • Guided tour, sample data
  • Usage/tracking metrics visible in app
  • Invite teammates + roles
  • Trial-to-paid conversion emails and in-app prompts
  • Referral and promo code flows


11 — Costs & infrastructure sizing (early stages)

  • Start small with managed services:
  • PostgreSQL managed DB (small tier)
  • Single modest app instance (Cloud Run / Heroku or small k8s node)
  • S3 storage
  • Stripe fees apply (standard)
  • Scale resources as usage grows; implement autoscaling rules for workers.


12 — Deployment checklist (pre-production)

  • Environment configs (secrets, env vars)
  • Run migrations on deploy (zero-downtime if needed)
  • Test webhooks and external integrations in staging
  • Set up TLS (Let’s Encrypt or managed)
  • Set up domain, DNS, CORS
  • Configure monitoring, alerts, escalation
  • Add backups and disaster recovery plan


13 — Example API endpoints (MVP)

  • POST /auth/register — register user
  • POST /auth/login — login (returns JWT)
  • GET /me — current user
  • POST /organizations — create tenant (admin)
  • GET /resources — list tenant resources
  • POST /resources — create resource
  • POST /stripe/webhook — handle Stripe events
  • GET /billing — billing summary
  • POST /billing/subscribe — start subscription


14 — Security & compliance quick list

  • HTTPS mandatory
  • Password hashing (bcrypt/argon2)
  • Webhook signature verification
  • Least privilege for credential
  • Audit logging for sensitive actions
  • Privacy: data retention, deletion workflows
  • GDPR/CCPA readiness (export, delete)


15 — Suggested timeline (small team: 1–3 devs)

  • Planning & infra (1–2 weeks)
  • Auth, tenant & skeleton (2–3 weeks)
  • Core product + DB (3–6 weeks)
  • Billing & payments (1–2 weeks)
  • Background jobs, storage, tests (2–3 weeks)
  • CI/CD, monitoring & deployment (1–2 weeks)
  • Beta & polish (2–4 weeks)

Total: ~10–18 weeks to MVP depending on scope and dev velocity.


16 — Starter repo layout (suggestion) 

/project-root
├─ backend/
│  ├─ app/
│  ├─ tests/
│  ├─ Dockerfile
│  └─ alembic/ or migrations/
├─ frontend/ (React/Next)
├─ infra/
│  ├─ k8s/
│  └─ terraform/ (optional)
├─ .github/workflows/ (CI)
└─ docs/


17 — Next steps I can do for you Pick one and I’ll produce it:

  • Generate a detailed API spec (OpenAPI) for your SaaS MVP.
  • Create a starter FastAPI project with auth, tenant model, basic endpoints, Dockerfile, and GitHub Actions.
  • Build Stripe webhook handler + subscription flow example.
  • Provide a security checklist and hardened config for production.
  • Draft a content/feature roadmap for first 6 months

Read the full article here: https://elshad-karimov.medium.com/building-a-saas-application-in-python-complete-roadmap-2c3e323821c0

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