Overview
Building a SaaS platform is not the same as building a web application. A web application serves users. A SaaS platform serves organisations — each with their own users, their own data, their own configuration, their own subscription, and their own expectations of availability, security, and performance. The architectural decisions that are easy to defer in a single-tenant web application — multi-tenancy, subscription management, tenant isolation, usage metering, per-tenant configuration — cannot be deferred in a SaaS platform without paying for it later in expensive retrofits or, worse, in production incidents that expose one customer's data to another.
SaaS platforms are also businesses, not just software. The platform needs to onboard customers efficiently, collect payments reliably, enforce subscription limits, provide the self-service account management that reduces support overhead, and give the operator the visibility into the platform's health and revenue that running a subscription business requires. The business infrastructure is as important as the product itself — a technically excellent platform that cannot bill correctly, cannot onboard customers without manual intervention, or cannot give operators visibility into churn is not a viable SaaS business.
We build SaaS platforms that address both dimensions from the start — the product that delivers value to customers, and the business infrastructure that makes delivering that product commercially sustainable. Multi-tenancy, authentication, subscription management, usage metering, self-service onboarding, operator tooling, and the performance and security architecture that enterprise customers require are all designed in rather than retrofitted.
What a SaaS Platform Requires
Multi-Tenancy Every SaaS platform serves multiple customers from shared infrastructure. The design of tenant isolation — how one customer's data is separated from another's, how one customer's load is prevented from affecting another's performance, how per-customer configuration is stored and applied — is the foundational architectural decision of any SaaS platform.
We design tenancy models appropriate to the platform's requirements and customer profile. Shared-schema tenancy with row-level security for platforms where cost efficiency and operational simplicity matter most. Separate schemas per tenant for platforms where stronger isolation is required. Separate databases for enterprise customers with compliance requirements that mandate it. The tenancy model is designed so that it can evolve — platforms that start with shared-schema tenancy can migrate specific customers to dedicated infrastructure as they grow and their requirements change, without rebuilding the platform.
Tenant isolation is enforced at multiple layers. At the application layer, tenant context established at authentication propagates through every request and is applied to every data operation. At the database layer, row-level security policies provide a defence-in-depth layer independent of application code. At the API layer, every resource access is validated against tenant ownership before data is returned or modified.
Authentication and Identity SaaS platforms serve diverse customer organisations with diverse identity requirements. Consumer-facing platforms need social login — Google, Apple, email magic link. Business platforms need username and password with MFA. Enterprise customers need SSO integration with their corporate identity provider via SAML or OIDC. The authentication architecture needs to support all of these without requiring separate implementations for each.
We implement authentication using Auth0 as the identity layer for most SaaS platforms — handling the full range of authentication methods, providing per-tenant SSO configuration for enterprise customers, and managing the token lifecycle that keeps users authenticated across sessions without requiring re-login on every visit. For Web3-enabled platforms, Privy provides the authentication infrastructure that bridges social identity with wallet-based on-chain identity.
Subscription and Billing A SaaS platform that cannot bill reliably is not a business. Subscription management — plan tiers, trial periods, upgrades and downgrades, usage-based billing components, failed payment handling, invoice generation, and the webhook processing that keeps subscription state in sync — is core infrastructure, not a feature to add later.
We integrate Stripe as the billing layer for SaaS platforms, handling the full subscription lifecycle from trial creation through payment collection through cancellation and churn. Plan configuration maps to feature access in the platform — a customer on a starter plan gets starter features, a customer who upgrades immediately gets access to the plan they have paid for, a customer whose payment fails has their access restricted automatically without manual intervention. Usage metering for consumption-based billing components tracks usage per tenant and reports it to Stripe for inclusion in monthly invoices.
Self-Service Onboarding SaaS businesses that require manual intervention to onboard each new customer do not scale. Every new customer should be able to sign up, configure their account, invite their team, connect their integrations, and start using the platform without a sales or operations team member doing anything. Automated onboarding that provisions the tenant's infrastructure, creates their initial admin user, initialises their subscription, and sends them everything they need to get started is the standard — not a premium feature.
We build onboarding flows that are fully automated and transactional — if any step fails, the partial onboarding rolls back cleanly rather than leaving a half-provisioned customer in a broken state. Onboarding instrumentation tracks where customers drop off in the onboarding flow so that friction points can be identified and addressed.
Usage Metering SaaS platforms with consumption-based billing components — API calls, active users, data storage, processed records, connected integrations — need usage metering infrastructure that accurately tracks consumption per tenant, aggregates it for billing periods, and feeds it into the billing system for invoice generation. Usage data is also surfaced to customers in their account dashboard so they can see their consumption against their plan limits before they hit them.
We build usage metering as a first-class infrastructure component — not bolted on as an afterthought after the product is built. Metering events are emitted from the application layer, aggregated server-side, stored with the accuracy and retention that billing requires, and reconciled against billing records to catch discrepancies before they become billing disputes.
The Product Layer
The product at the centre of the SaaS platform — the capability that customers pay for — is built on the same professional stack we use for all production software:
React and Next.js for the customer-facing frontend — the application the customer uses, their account management interface, onboarding flows, and the self-service configuration that lets customers set up and manage their account without support intervention.
Rust / Axum for performance-critical backend services — API endpoints that need to handle high concurrency, real-time data delivery, processing pipelines, and any component where the performance characteristics of Rust's async runtime provide meaningful advantages over managed-runtime alternatives.
C# / ASP.NET Core for complex backend services — business logic heavy components, enterprise system integrations, and services where the .NET ecosystem's breadth of integration libraries and mature tooling is the right fit.
PostgreSQL as the primary data store for most SaaS platforms — with the analytical query capabilities, row-level security, and operational maturity that production SaaS platforms require.
Redis for session management, per-tenant caching, rate limit state, job queues, and the real-time pub/sub infrastructure that live features depend on.
Platform Administration
Running a SaaS platform requires operational visibility and control that is distinct from the product the customers use. The platform operator needs tooling to manage the customer base, understand platform health, and intervene when customers need support.
Customer management. A complete view of every customer on the platform — their subscription status, their usage metrics, their active users, their configuration, their support history. The ability to impersonate a customer session for support purposes, with full audit logging of every impersonation event. Bulk operations for plan changes, feature flag adjustments, and configuration updates that need to be applied across a set of customers.
Revenue and business metrics. Monthly recurring revenue, annual recurring revenue, new customer count, churn rate, average revenue per account, and the cohort-level metrics that tell the story of the business's growth trajectory. Trial-to-paid conversion rates and time-to-conversion. Usage metrics across the customer base that surface which features drive engagement and retention.
Platform health monitoring. Per-tenant error rates, API latency, and the signals that indicate a customer is experiencing problems — surfaced to the operator before the customer raises a support ticket. Queue depths, background job performance, and infrastructure health metrics that surface operational issues before they affect customer experience.
Feature flag management. The ability to enable and disable features per customer, per plan tier, or platform-wide — for gradual rollouts, beta access programs, A/B testing, and the management of feature access as part of plan differentiation — from an administrative interface rather than requiring code deployments.
Security for SaaS
SaaS platforms are a high-value target. They hold data for many customers in a single system, they are accessible from the internet, and a single security failure can affect all customers simultaneously. Security is not optional and it is not a feature to add after launch.
Data isolation at depth. Tenant isolation enforced at application, database, and API layers as described above. No single layer of isolation is trusted to be sufficient — the system is designed so that a failure at one layer does not result in cross-tenant data exposure.
Encryption at rest and in transit. Customer data encrypted at rest using database-level and storage-level encryption. All data in transit encrypted via TLS with current cipher suites. Encryption key management appropriate to the sensitivity of the data and the compliance requirements of the customer base.
Secret and credential management. API keys, integration credentials, and other secrets stored in encrypted configuration stores — never in code, never in unencrypted database columns, never in log output. Per-tenant credentials isolated from each other with access controls that prevent cross-tenant credential access.
Rate limiting and abuse prevention. Per-tenant and per-user rate limits at the API layer that prevent any single customer or user from consuming disproportionate resources or conducting credential stuffing and enumeration attacks. Anomaly detection on authentication patterns that surfaces unusual access behaviour.
Audit logging. A complete, tamper-evident log of every significant action taken on the platform — authentication events, data access, configuration changes, administrative actions, billing events. Audit logs are retained for the period required by compliance obligations and are accessible to customers for their own account's events through the account management interface.
Scalability Architecture
A SaaS platform that works for a hundred customers needs to still work — and work well — for ten thousand. The architectural decisions that determine scalability are made at the beginning.
Stateless application services. Application servers hold no state between requests. Session state is held in Redis, not in process memory. This means any application instance can serve any request, and scaling is a matter of adding instances rather than re-architecting the state management.
Database read replicas. Analytical queries, reporting, and read-heavy operations are routed to read replicas rather than the primary database. The write path remains uncongested as read traffic grows.
Background job queues. Work that does not need to happen synchronously with a user request — sending emails, processing webhooks, generating reports, running scheduled jobs — is queued and processed by background workers that scale independently of the API layer.
Per-tenant rate limiting. No single tenant can generate enough load to degrade the platform for other tenants. Rate limits are enforced per tenant at the API gateway and tracked in Redis for distributed enforcement across application instances.
Horizontal scaling. The platform scales horizontally — adding application instances behind a load balancer — rather than requiring increasingly large single instances. This keeps scaling incremental, avoids single points of failure, and allows the platform to handle traffic spikes without pre-provisioning capacity for peak load permanently.
Technologies Used
- React / Next.js — customer-facing product frontend, account management, onboarding flows
- TypeScript — type-safe frontend and backend code throughout
- Rust / Axum — high-performance API services, real-time data delivery, processing-intensive backend components
- C# / ASP.NET Core — complex backend services, enterprise integrations, business logic-heavy components
- PostgreSQL — primary multi-tenant data store, row-level security, analytical query capability
- Redis — session management, per-tenant caching, rate limit state, job queues, pub/sub
- Auth0 — authentication, social login, MFA, per-tenant enterprise SSO
- OAuth2 / OIDC — enterprise identity provider integration for SSO customers
- Privy — Web3 authentication and embedded wallet infrastructure for onchain SaaS platforms
- Stripe — subscription management, usage metering, billing, invoice generation
- AWS EC2 / S3 / SQS — cloud infrastructure for scalable platform deployment
- Systemd / Linux — reliable service management for platform backend components
When to Build SaaS Architecture From the Start
The temptation with SaaS platforms is to start simple — build the product for the first customer, add multi-tenancy when there is a second customer, add billing when someone is ready to pay. This approach is understandable and sometimes appropriate, but it has a cost that is easy to underestimate: the retrofit of multi-tenancy, billing, and security architecture onto a system built without them is expensive, disruptive, and carries the risk of introducing the data isolation failures that would be most damaging to a SaaS business's reputation.
For platforms that will serve multiple customers — even if they start with one — building the SaaS architecture from the start is lower total cost than building it twice. The incremental cost of multi-tenancy, billing integration, and security architecture at the beginning of the project is a fraction of the cost of adding them to a system designed without them.
Build Your SaaS Platform
Whether you are launching a new SaaS product, converting an existing single-tenant application into a multi-tenant platform, or rebuilding a platform that has outgrown its original architecture — we have the experience to design and deliver it correctly.