Socket.IO dependency has been upgraded to 3.x.
If you are using clustering redis is now a requirement. Simply install and configure redis in your config.json block. If you were already using redis as your datastore or for sessions no changes are necessary.
The other change is for the
socket.io:origins property in config.json. If you were using this property to allow access to websockets from multiple domains you will have to convert it to an array.
"origins": "https://community.nodebb.org:*, https://nodebb.org:*"
"origins": ["https://community.nodebb.org:*", "https://nodebb.org:*"]
For a list of all available options see here
No changes are necessary if you weren't using this property.