We do have limitations in place in regards to the connectivity of a function. Only HTTP/HTTPS-based protocols are supported. The outgoing communication routes through a proxy, which enforces the whitelist and the rate limit.
Right now we offer a HTTPClient and a MTLSClient over our Toolbelt, that are configured to communicate with the proxy. If the request is trying to access a destination that was not whitelisted, the proxy will close the connection yielding a socket closed error.