How do you integrate Redis as a session store in a web application?

Using Redis for session storage means each user's session data (login state, cart contents, preferences) is stored as a Hash or JSON-serialized String under a key derived from a session ID, with a TTL matching the desired session lifetime — instead of relying on server-local in-memory session storage, which breaks as soon as requests are load-balanced across multiple application servers.

HSET session:abc123 user_id "1001" cart_items "3"
EXPIRE session:abc123 1800   # 30-minute session timeout

Most web frameworks (Express with connect-redis, Spring Session with its Redis integration, Django with django-redis, and others) provide a ready-made session store adapter, so the application typically doesn't hand-roll this logic — it configures the framework to use Redis as the session backend and gets automatic session read/write/expiry wired in. The key operational benefit over local in-memory sessions is that any application server instance can serve any request for a given session, since session state lives centrally in Redis rather than pinned to whichever server first created it, which is exactly what makes horizontal scaling and rolling deployments practical for a stateful-feeling web application.