Let's take an usual express setup; we have app for che express app, io for the session.io, and we have to know where is the redis server. So,
require('redis-io-session')(app, io, {
REDIS_HOST: 127.0.0.1,
REDIS_PORT: 6379,
SESSION_SECRET: 'kitty'
});
After that, you can reach the session data from the socket:
socket.handshake.session