Second... I guess I can reiterate. Riemann is not an HTTP server. It's an event-stream driven monitoring system. The protocol uses existing standards (e.g. protobufs), is simple to implement, and the community has written clients for many languages: http://riemann.io/clients.html.
As an aside, I do plan on adding an HTTP interface to Riemann, but HTTP processing (and using JSON for serialization) comes with certain unavoidable costs in bandwidth, memory and latency. It'll fill a complementary space to the existing TCP and UDP interfaces.
I completely agree that for specific uses Riemann is great. Your post was, though, about the performance/throughput, and so my comment was about the performance/throughput. Streaming messages/events over the network is an old problem, with well-known limitations, and this was what my comment was about.
And if a system designer wants to send a stream of "events" to another system to be acted upon, and if this designer cares about throughput (which is assumed here, given the title of the post), then this designer is likely to choose a faster messaging system, especially if it is more flexible, due to its ubiquity and universal support, protocol (e.g. HTTP) over a custom protocol.
If you are trying to make sense of Riemann in HTTP terms, sending an event to Riemann might look like POST /streams, with a body containing a single JSON object. There's no notion of GET, PUT, or DELETE though--the state inside Riemann streams has no name or external representation.
There are other components in Riemann which can be expressed as HTTP resources--the index, which is used for tracking the most recent event for a given host and service, and the pubsub system for example. Those have HTTP APIs for making a query (GET /index?q=service = "www" and state = "critical"), and a websocket variant which streams down updates for that query to you.
But as far as a general replacement, I'd say no, it doesn't make any sense. This is more akin to... a slow, insanely flexible, less complete version of Esper than an HTTP server.
Coincidentally, I was just working on a tracing system to dump data to Riemann while eating HTTP logs and/or handling live requests from browsers. It seems to be just what we need to aggregate, monitor and graph our trace data. Thanks!
BTW, you're not the first to wonder about streaming events directly to Riemann from client browsers. I... don't recommend it, just because I don't have the time to appropriately guarantee Riemann's performance and security characteristics as an internet-facing service (yet), but adding an HTTP POST path to (ws-server) is definitely on my list. Even if the HTTP+JSON interface is much slower than the TCP/UDP interfaces, I think it'll be plenty useful for many deployments, especially those making requests from JS.