Anecdotally, non-multicast setups are easier to scale in hardware (because you can push commodity farther) and most critically are easier for the normal type of engineer you'd find in the tech sector to reason about (because many aren't comfortable with networking equipment, so it's much easier moving that state out of the network and into layers they can easily debug).

At any rate, most cloud SDNs don't support IP multicast (unless you use an overlay like Weave), so it's sort of a nonstarter for them.

These days I might use Redis pub/sub along with a multi-level cache (e.g. LMDB + local Redis + remote Redis) if I need to distribute data to a large number of clients efficiently.

You can, of course, use Rendezvous without multicast.

And: does anyone still use it? The last exchange I worked with that did was migrating from it to JMS (which sort of gives lie to the idea that Rendezvous's multicast performance was that big a deal).

Now that 10Gb+ is commonplace and modern servers can service hundreds or thousands of message bus consumers with efficient kernel-managed event loops, yes, it's arguably less needed now. But nobody will claim it's efficient from a network perspective. :)

Is well regarded & open source

https://www.nasdaqtrader.com/content/technicalsupport/specif...

It is actually quite good.

FWIW when you talk about different requirements, I'm not sure you're correct. For traders, sure, oftentimes they can just dump old data if they fall behind because it's mostly irrelevant. However, stock exchanges have performance and reliability/availability as top requirements. They must record all transactions and can't crash or lock-up. Most use multicast internally and externally. They would never be able to scale and maintain a low response time with TCP.

In a dynamic environment where you'd be scaling continuously and adding components and servers and building new services, this becomes a non-starter. Multicast implementations doesn't fail gracefully -- there's very little warning before things come to a complete halt and need complete shutdown and reboot of entire network.