FAQ¶

Networking¶

Why does Sen use multicast?

When you have n participants, multicast allows for much better scaling. When producers send messages to multiple consumers, multicast relies on the router hardware to do it fast and efficiently. The producer does not have to allocate n buffers and send n messages, and the network does not get loaded with n messages that contain the same information. It differs from broadcast in the sense that it also prevents unwanted traffic from reaching networks where there are no consumers. Multicast also serves as a way to isolate and segregate data flows that have to be logically or physically separated in some contexts.

Can I force the usage of TCP?

Yes. You can force bus communication to be done over TCP by configuring the ether component in your yaml file, or by setting the SEN_ETHER_DISABLE_BUS_MULTICAST environment variable to true. Remember to do so in all the involved Sen instances.

What if the infrastructure does not allow me to use Multicast?

Apart from forcing the usage of TCP for bus communication, you need to change the way in which Sen instances discover each other. You can do that by setting the discovery configuration field of the ether component to TcpDiscovery. This mechanism works by instantiating a "discovery hub" that Sen instances connect to in order to know about each other's existence. Have a look at the documentation of the ether component for more information and some examples.

Can messages be lost when using a non-confirmed quality of service?

In theory, yes. In practice, it is unlikely in most cases. UDP (multicast or unicast) does not offer any guarantee in terms of confirmation of reception and order of delivery. That said, when working in Local Area Networks (which is the typical case for Sen applications), it is very hard to lose a UDP datagram. You would need to have a very loaded network, a faulty firewall or some sort of infrastructural problem that would cause it.

Do I need a network to run my Sen-based application?

If you don't load the ether component, all the sessions and buses are local.

WSL2¶

Can I use Sen with WSL2?

Yes, with some networking limitations. Configure WSL2 to use mirrored networking, ensure the selected interface and firewalls allow multicast, and raise the open-file limit. Communication has been verified with remote Linux and Windows hosts, but not between WSL2 and the Windows host running it. See Networking with WSL2 and virtual machines for the complete setup and the TCP-only fallback.