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System Design Masterclass · Cloud Infrastructure
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In 2005, if you wanted email for your company, you bought a server, installed Microsoft Exchange, hired someone to maintain it, managed backups, handled security patches, and dealt with outages. For email.
In 2026, you sign up for Google Workspace or Microsoft 365. Done. Email, calendar, documents, video calls, running in seconds. No servers. No installation. No maintenance. The provider handles everything. You just use the software.
That's SaaS. Software as a Service. You don't manage infrastructure (that's IaaS). You don't manage platforms (that's PaaS). You don't even manage the application. It's fully built, fully hosted, and fully managed. You just log in and use it.
SaaS represents the highest level of abstraction in cloud computing. As a system design engineer, you'll both use SaaS products (Datadog for monitoring, PagerDuty for alerting, Stripe for payments) and potentially build SaaS products for others.
| Model | You Manage | Provider Manages |
|---|---|---|
| IaaS | OS, runtime, app, data | Hardware, network, hypervisor |
| PaaS | App code, data | OS, runtime, scaling, infra |
| SaaS | Data (sometimes config) | Everything else |
SaaS characteristics:
SaaS in system design: You don't build everything from scratch. A well-architected system uses SaaS for undifferentiated work:
| Need | Build It? | SaaS Alternative |
|---|---|---|
| Payment processing | No | Stripe, Razorpay |
| Email delivery | No | SendGrid, Postmark |
| Monitoring | Maybe | Datadog, New Relic |
| Authentication | Maybe | Auth0, Clerk |
| Search | Maybe | Algolia, Cloud |
| Analytics | No | Mixpanel, Amplitude |