Scaling NodeJS chat room - store connection status in Redis

Question

The chat room app are running on multiple servers and consists two services:
1. connection manager
Before joining the chat room, client ask for a chat service url from connection manager first
2. chat service
A typical socket.io based chat implementation.

I need to store each client's connection status in Redis, such as user connect to which room, how many users are in one room etc. So the connection manager can use the data to do load balancing.

I can use socket connection/disconnect event to maintain the current connection status in Redis, but in case of NodeJS server failure, how to make sure Node and Redis data are synchronized? What's the best way to do this?

Answer 1

I can use socket connection/disconnect event to maintain the current connection status in Redis, but in case of NodeJS server failure, how to make sure Node and Redis data are synchronized?

For example you can create a set in redis which would contain reference to keys that are managed by specific server node. If a node goes down or is restarted you can invalidate these keys.