No. Each worker in a Node.js cluster is a separate OS process with its own isolated memory space. Workers cannot share variables or in-memory state. Shared state must be managed using external tools like Redis, a database, or IPC messaging.
This is a fundamental limitation of the process-based clustering model. Unlike threads, OS processes have completely separate memory spaces. Any in-memory data — such as session stores, counters, or cached data — will be duplicated independently in each worker and not synchronized. This is a major architectural consideration when building clustered applications.
User sessions may not persist across requests if different workers handle them
In-memory caches are duplicated and can go out of sync between workers
Counters or rate-limiters stored in memory will be inaccurate across workers
WebSocket connections are tied to a specific worker and not portable to others
Redis — most common solution for sessions, caching, pub/sub, and rate limiting
Database (MongoDB, PostgreSQL) — for persistent shared state across workers
IPC Messaging — workers send state to master, which aggregates and rebroadcasts
Sticky Sessions — route same client to same worker (partial solution, not true sharing)
Memcached — in-memory distributed cache for high-speed shared data