If you need to allow IPs or FQDNs, below is the addresses Composer connects to.
Composer uses HTTP or HTTPS ports (80, 443) for communication with Cloud.
WebSockets will be used over above ports to allow direct client-to-server connection. These connections require support for Keep Alive HTTP connections.
Usually no change in network firewall or similar is necessary. Connections from Composer is outbound, so there are no need to open any inbound ports.
We do not recommend having Composer behind a proxy or similar network technology.
Contact support if you need more details.