Web Aplikacije & SaaS Sistemi: Kompletan Vodič za 2025

💡 Šta su Web Aplikacije i SaaS Sistemi?

Web aplikacije su dinamički programi koji se izvršavaju u browseru i komuniciraju sa serverom. SaaS (Software as a Service) su web aplikacije isporučene kao pretplatnički servis gde korisnici plaćaju mesečno/godišnje umesto da kupuju licencu.

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Poslovne aplikacije

CRM, ERP, Project Management, HR sistemi

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Klijentski portali

Self-service platforme, ticket sistemi, dashboards

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SaaS Platforme

Multi-tenant cloud aplikacije sa pretplatama

📊 Trend: SaaS industrija je vredna $195 milijardi u 2023. godini i raste po stopi od 18% godišnje. Očekuje se da dostigne $700+ milijardi do 2030.

🎯 Tipovi Web Aplikacija

Različiti biznis potrebe zahtevaju različite arhitekture i pristupe:

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Internal Business Apps

Aplikacije za internu upotrebu u kompaniji – timovi, procesi, workflow.

Single organization (single-tenant)
Integrisane sa AD/LDAP
Complex business logic
Custom reports & analytics

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Customer Portals

Self-service platforme gde klijenti upravljaju svojim nalozima, porudžbinama, ticketima.

Account management
Order history & tracking
Support tickets
Knowledge base

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Multi-Tenant SaaS

Cloud aplikacije gde stotine/hiljade kompanija dele istu infrastrukturu.

Shared infrastructure, isolated data
Subscription billing
Multi-organization support
Tiered pricing (Starter/Pro/Enterprise)

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Marketplace Platforms

Platforme koje povezuju kupce i prodavce – Airbnb, Uber, Upwork model.

Multi-sided marketplace
Vendor dashboards
Commission & payout logic
Rating & review sistem

🏗️ Moderna arhitektura Web aplikacija

Tipičan tech stack za SaaS aplikaciju:

Frontend – React/Vue/Angular + TypeScript za dinamički UI

Backend API – Node.js/Python/Java REST ili GraphQL API

Database – PostgreSQL/MySQL za relacijske, MongoDB za NoSQL potrebe

Cache Layer – Redis za session storage, rate limiting, caching

File Storage – AWS S3 / Azure Blob za dokumente, slike, uploads

Queue System – RabbitMQ/Redis Queue za async tasks (email, exports)

Monitoring – Sentry (errors), DataDog/New Relic (performance)

Microservices

Za enterprise scale

Razdvojena arhitektura za skalabilnost i resilience

Monolith

Za startup MVP

Jednostavnija deploy, debugging i development brzina

Serverless

Za optimizaciju troškova

AWS Lambda/Vercel Functions – plaćate samo usage

🔐 Autentifikacija i Autorizacija

Svaka ozbiljna web aplikacija mora imati robusnu authentication i authorization strategiju:

🔑 Ključni koncepti bezbednosti:

Authentication (AuthN) – Ko si ti? (login sa username/password, OAuth, SSO)

Authorization (AuthZ) – Šta smeš da radiš? (permissions, roles, RBAC)

JWT Tokens – Stateless auth sa access + refresh token strategijom

OAuth 2.0 / OpenID Connect – "Sign in with Google/Microsoft"

Multi-Factor Authentication (MFA) – SMS/Email/Authenticator app za dodatnu zaštitu

Session Management – Logout, expire old sessions, concurrent login handling

Password Security – Bcrypt/Argon2 hashing, password policies, reset flow

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Role-Based Access Control (RBAC)

Hijerarhija permisija po ulogama korisnika:

Super Admin – Puna kontrola nad svim organizacijama i korisnicima
Admin – Upravlja svojom organizacijom, dodaje/briše users, menja settings
Manager – Može da vidi sve projekte, dodeljuje taskove timu
Member – Pristup samo projektima gde je assignovan
Guest/Viewer – Read-only pristup, ne može da menja ništa

⚡ Best Practice:

Koristite Auth0, Supabase Auth, ili AWS Cognito umesto da sami implementirate auth od nule. Greške u security koštaju skupo – verujte proven rešenjima.

💰 Subscription Management & Billing

Za SaaS biznis, billing sistem je srce aplikacije. Mora biti pouzdan, skalabilan i fleksibilan:

Plan Selection

Korisnik bira plan (Starter/Pro/Enterprise) – pricing page sa feature comparison.

Onboarding

Payment Setup

Payment method capture (Stripe Checkout) – card details tokenizovani, spremljeni za recurring.

Checkout

Subscription Active

Aktiviran pristup svim features plana. User dobija pun access do app-a.

Live

Recurring Billing

Automatska naplata svakog meseca/godine. Invoice se šalje emailom.

Monthly

Upgrade/Downgrade

User može promeniti plan mid-cycle – prorated billing se primenjuje.

Anytime

Churn Management

Failed payment retry logic (dunning), grace period, cancelation flow sa retention offers.

Retention

💳 Stripe Billing

De-facto standard za SaaS billing. Subscription management, invoicing, tax calculation, customer portal – sve out of the box.

📊 Chargebee / Paddle

Alternative sa više business features – dunning campaigns, revenue recognition, advanced analytics.

🔗 API Integracije i Ekosistem

Moderne aplikacije retko postoje izolovano – integracije sa drugim servisima su ključne:

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Email Service

SendGrid, Mailgun, AWS SES – transakcijski i marketing emailovi

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Communication

Twilio (SMS), Slack API, Discord webhooks – notifikacije

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Analytics

Google Analytics, Mixpanel, Amplitude – user behavior tracking

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Payment

Stripe, PayPal, Square – online plaćanja i billing

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Cloud Storage

AWS S3, Cloudinary, Azure Blob – file uploads i media

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Search

Algolia, Elasticsearch – brza full-text pretraga

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Maps & Location

Google Maps API, Mapbox – geolocation i mape

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AI/ML Services

OpenAI API, Google Cloud AI – chatbots, predictions

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Document Gen

DocuSign, PDF.co – PDF generation, e-signatures

🔧 API Best Practices: Rate limiting (100 req/min per user), API versioning (v1, v2), pagination za liste, proper error messages (401, 403, 429), API documentation (Swagger/OpenAPI).

Klijentski portali – Ključne features

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Account Management

Self-service zona gde klijent upravlja svojim profilom i podacima.

Profile editing (ime, email, adresa, preferencije)
Password change & security settings
Subscription details & plan management
Payment method update & billing history

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Order & Usage Tracking

Pregled svih transakcija, porudžbina i history aktivnosti.

Order history sa filterima i searchom
Real-time status tracking (pending, shipped, delivered)
Download invoices i receipti u PDF-u
Usage dashboards (API calls, storage, bandwidth)

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Support & Ticketing

Integrisan sistem za customer support direktno u portalu.

Submit support tickets sa attachments
Real-time chat sa support agentima
Knowledge base i FAQ search
Ticket history i status updates

⚡ Performance & Skalabilnost

🚀 Caching Strategije

Redis za session data, aplikativni cache (hot data), rate limiting counters. CDN (Cloudflare/CloudFront) za static assets.

📊 Database Optimization

Indexing, query optimization, read replicas za read-heavy operations, connection pooling, periodic vacuum/analyze.

⚖️ Load Balancing

NGINX/HAProxy za distribuciju traffica na multiple server instances. Auto-scaling u cloud-u (AWS ECS, Kubernetes).

🔄 Async Processing

Background jobs za heavy tasks (email sending, file processing, reports). Queue systems – Celery, Bull, SQS.

< 200ms

API Response Time

Target za 95th percentile – optimizuj query-je

99.9%

Uptime SLA

Three nines standard – max 43 min downtime mesečno

10k+

Concurrent Users

Skalabilnost za rast – testiranje sa load testing tools

Security Best Practices

🛡️ Checklist za bezbednu aplikaciju:

HTTPS svuda – SSL/TLS certifikati (Let's Encrypt besplatno)

Input validation & sanitization – zaštita od XSS, SQL injection

CSRF tokens za sve POST/PUT/DELETE requests

Rate limiting – max 100 API req/min per user

Security headers – CSP, X-Frame-Options, HSTS

Regular dependency updates – npm audit fix, security patches

Audit logging – ko je šta radio i kada (compliance)

Data encryption at rest – sensitive podaci enkriptovani u bazi

Backup strategy – daily backups sa retention policy

🎯 Ključni zaključci

Web aplikacije i SaaS sistemi su budućnost software industrije

Investirajte u robusnu authentication/authorization od početka

Za SaaS, subscription billing mora biti pouzdan – koristite Stripe

RBAC je ključan za enterprise aplikacije – planirati role hijerarhiju

API integracije proširuju funkcionalnost bez razvoja od nule

Performance i security nisu opcije – built-in od dana 1

Klijentski portali smanjuju support load – self-service je kralj

Web Aplikacije & SaaS Sistemi: Kompletan Vodič za Razvoj