Series · 6 parts
Billing and tenant isolation for a solo Laravel + PostgreSQL SaaS: leak-proof scoping with Row Level Security, idempotent Stripe webhooks, plan-model invoice math, proration, dunning and per-tenant limits. Measured failures, not package tutorials.
Curriculum progress0 of 6 parts completed (0%)
Estimated remaining time: 55 minutes
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Laravel tenant scopes built on a tenantid global scope do not isolate tenants. In a lab with 200,000 invoice rows across 100 tenants, the scope leaked all 200,000 rows in 5 of 7 common query paths.
Key finding
A Laravel global scope on tenant_id leaked all 200,000 rows to tenant 7 in 5 of 7 query paths: raw queries, withoutGlobalScopes(), queued jobs and joins.
Stripe delivers each webhook at least once, so a Laravel handler that credits an account on every delivery credited 5x in my lab, once per retry. In a lab with 20 paid invoices and 5 deliveries of
For a solo Laravel SaaS where customers differ a lot in how much they use, a hybrid plan is the safest default: a base fee that includes some usage, then a metered rate above it. In a 1,000-customer
Laravel Cashier's default swap() and updateQuantity() calls do not charge a customer for an upgrade today. They send prorationbehavior=createprorations, so Stripe adds the charge to the next renewal
Laravel Cashier locks customers out on day 0 of Stripe's retry window. The first failed renewal moves a subscription to pastdue, and Cashier's valid() returns false from that moment. Stripe's
Laravel's RateLimited job middleware protected a small tenant from a noisy one, and it also failed 240 of the noisy tenant's 300 jobs. In my lab, a limit of 20 jobs per second kept the small tenant's
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Continuous dispatch
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6 parts · 60 min
System design for AI-powered SaaS at solo scale: LLM unit economics, multi-tenant isolation, usage billing, durable agent jobs, RAG storage and scaling drills. Measured numbers, not interview diagrams.
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