Replit Architecture Variants

Overview

Application architectures on Replit at different scales. Replit's container model, built-in database, and Deployments feature support architectures from simple scripts to production web services.

Prerequisites

• Replit account (Free, Hacker, or Pro)
• Understanding of Replit's container lifecycle
• Awareness of plan-specific resource limits

Instructions

Step 1: Single-File Script (Prototype)

Best for: Scripts, bots, automation, learning.

# main.py - everything in one file
from flask import Flask
from replit import db

app = Flask(__name__)

@app.route('/')
def home():
    count = db.get("visits") or 0
    db["visits"] = count + 1
    return f"Visit #{count + 1}"

app.run(host='0.0.0.0', port=int(os.environ.get('PORT', 3000)))  # 3000: 3 seconds in ms

Limits: Sleeps after inactivity (free plan). 512MB RAM. Replit DB (50MB).

Step 2: Modular App with External DB (Production)

Best for: Web apps, APIs, 100-10K daily users.

Replit Deployment -> External PostgreSQL (Neon/Supabase)
                  -> External Redis (Upstash)
                  -> External Storage (S3/Replit Object Storage)

# Structured project layout
# main.py -> routes/ -> services/ -> models/
import os
from flask import Flask
from sqlalchemy import create_engine

app = Flask(__name__)
engine = create_engine(os.environ["DATABASE_URL"])  # External Postgres

# Use Replit Deployments for always-on
# Use external DB for persistence beyond container lifecycle

Step 3: Multi-Service with Replit Deployments (Scale)

Best for: Production services, microservices, 10K+ daily users.

CDN (Cloudflare) -> Replit Deployment (API)
                         |
                    External DB (Neon Postgres)
                    External Cache (Upstash Redis)
                    External Queue (Upstash Kafka)
                         |
                    Replit Deployment (Worker)

# API service (Replit Deployment 1)
# Worker service (Replit Deployment 2)
# Each in its own Repl with own Deployment
# Communicate via shared database/queue

Decision Matrix

Factor	Single-File	Modular + External DB	Multi-Service
Users	Prototype	100-10K/day	10K+/day
Database	Replit DB	External Postgres	External + cache
Persistence	Ephemeral	Durable	Durable
Cost	Free	$7-20/mo	$20+/mo
Always-on	No (free)	Yes (Deployment)	Yes

Error Handling

Issue	Cause	Solution
Data loss	Using filesystem/Replit DB	Migrate to external database
Container sleeping	Free plan limitations	Use Deployments or keep-alive
Memory limit	Large in-memory datasets	Stream data, use external storage

Resources

• Replit Deployments
• Replit Database Options

Output

• Configuration files or code changes applied to the project
• Validation report confirming correct implementation
• Summary of changes made and their rationale

Examples

Basic usage: Apply replit architecture variants to a standard project setup with default configuration options.

Advanced scenario: Customize replit architecture variants for production environments with multiple constraints and team-specific requirements.