replit-known-pitfalls

# Replit Known Pitfalls ## Overview Real gotchas when building on Replit. Each pitfall includes what goes wrong, why, and the correct pattern. Based on common failures in Replit's ephemeral container model, Nix-based environment, and cloud hosting platform. ## Pitfall Reference ### 1. Writing to Local Filesystem for Persistence **What happens:** Data is lost when the container restarts, deploys, or sleeps. ```python # BAD — files disappear on container restart with open("user_data.json", "w") as f: json.dump(data, f) # GOOD — use Replit's persistent storage from replit import db db["user_data"] = data # For files, use Object Storage from replit.object_storage import Client storage = Client() storage.upload_from_text("user_data.json", json.dumps(data)) ``` **Rule:** Anything written to the filesystem is ephemeral. Use PostgreSQL, KV Database, or Object Storage for data that must survive restarts. --- ### 2. Hardcoding Secrets in Source Code **What happens:** Secrets are visible to anyone who views your Repl (public by default on free plans). Replit's Secret Scanner catches some cases but not all. ```python # BAD — exposed in public Repl API_KEY = "sk-live-abc123" DATABASE_URL = "postgresql://user:password@host/db" # GOOD — use Replit Secrets (lock icon in sidebar) import os API_KEY = os.environ["API_KEY"] DATABASE_URL = os.environ["DATABASE_URL"] ``` --- ### 3. Binding to localhost Instead of 0.0.0.0 **What happens:** App starts but Webview is blank. Replit's ...