Launching a B2B SaaS platform in Spain: what no architecture tutorial tells you

Architecture decisions that define the product

• 2026 stack for high-performance B2B SaaS: Next.js 14 (frontend + SSR), Node.js/Python (API), PostgreSQL with Row-Level Security (data), Redis (cache and queues), Vercel/AWS (infrastructure). This stack has enough talent available in Spain to scale the team without friction.
• The REST vs. GraphQL API decision must be made in month 1: GraphQL facilitates the complex B2B client dashboards but adds complexity. REST is better for integrations with external systems (ERP, CRM, client systems).
• Authentication and authorisation from the first sprint: JWT + RBAC (Role-Based Access Control) with roles at organisation (tenant), team, and individual user level. Adding this later is 3-5x more expensive.
• Observability from the start: structured logs, per-tenant usage metrics, and performance degradation alerts. Production problems you can't see are the ones that lose customers.

Multitenant by design: the mistake you cannot make in month 1

• The biggest technical mistake in B2B SaaS is not designing the multitenant architecture from the beginning: migrating from a monolithic database to multitenant after launch is a 2-4 month project that paralyses feature development.
• Three multitenant models and when to use each: shared database with row-level security (cheapest, valid for most B2B SaaS), schema per tenant (greater isolation, more complex), database per tenant (maximum isolation, only for enterprise with regulatory requirements).
• Every new feature must be designed thinking about which data belongs to the tenant (private) and which belongs to the platform (shared): this design discipline is the difference between a scalable SaaS and one that breaks when adding customer number 50.
• Implement tenant context in middleware from day one: all database queries must automatically include the tenant_id filter without depending on the developer to remember it in each operation.

From technical MVP to the first paying account

• A viable B2B SaaS MVP has exactly three things: the onboarding flow for a new client (registration, initial setup, first value delivered), the core functionality that solves the main problem, and a basic billing system (even if manual at first).
• The most common go-to-market mistake in Spanish B2B SaaS: building 6 months of features before putting the product in real customers' hands. Feedback from 3 customers paying €300/month each is worth more than 3 additional months of development.
• Initial pricing: start with annual pricing (improves cashflow and reduces churn), offer 20% discount for annual payment, and don't start with freemium (B2B clients who don't pay from the start rarely convert).
• The first 10 paying accounts in B2B SaaS come from direct sales, not SEO or ads: the founder or CEO must be the first salesperson for the first 6-12 months.

Dockia for B2B SaaS: from 0 to MVP in 8-12 weeks

• Dockia builds B2B SaaS MVPs with multitenant architecture from the first sprint: no need to refactor to scale because the design already accounts for it.
• Our 8-12 week process for B2B SaaS MVP: weeks 1-2 (architecture + data design), weeks 3-6 (authentication, multitenant, core functionality), weeks 7-10 (onboarding, billing, admin panel), weeks 11-12 (testing, optimisation, launch).
• The Enterprise plan (€2,000) covers the first complete sprint with validated architecture and first functionality in production. It is the right entry point before committing the full MVP budget.
• We deliver the MVP with complete documentation, client-owned repository, and knowledge transfer: when the internal team grows, they can continue without depending on Dockia.

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