NDAA passed: Internet and Online Streaming Services Emergency Alert Study

Sun Jan 3 21:35:35 UTC 2021

On 1/3/21 4:22 PM, Mark Delany wrote:
> Creating quiescent sockets has certainly been discussed in the context of RSS where you
> might want to server-notify a large number of long-held client connections very
> infrequently.
> 
> While a kernel could quiesce a TCP socket down to maybe 100 bytes or so (endpoint tuples,
> sequence numbers, window sizes and a few other odds and sods), a big residual cost is
> application state - in particular TLS state.
> 
> Even with a participating application, quiescing in-memory state to something less than,
> say, 1KB is probably hard but might be doable with a participating TLS library. If so, a
> million quiescent connections could conceivably be stashed in a coupla GB of memory. And
> of course if you're prepared to wear a disk read to recover quiescent state, your
> in-memory cost could be less than 100 bytes allowing many millions of quiescent
> connections per server.
> 
> Having said all that, as far as I understand it, none of the DNS-over-TCP systems imply
> centralization, that's just how a few applications have chosen to deploy. We deploy DOH to
> a private self-managed server pool which consume a measly 10-20 concurrent TCP sessions.

I was thinking more in the original context of this thread w.r.t. 
potential distribution of emergency alerts.  That could, if 
semi-centralized, easily result in 100s of million connections to juggle 
across a single service just for the USA.  While it presumably wouldn't 
be quite that centralized, it's a sizable problem to manage.

Obviously you could distribute it out ala the CDN model that the content 
providers use, but then you're potentially devoting a sizable chunk of 
hardware resources at something that really doesn't otherwise require it.

The nice thing is that such emergency alerts don't require 
confidentiality and can relatively easily bear in-band, 
application-level authentication (in fact, that seems preferable to only 
using session-level authentication).  That means you could easily carry 
them over plain HTTP or similar which removes the TLS overhead you mention.

Several GB of RAM is nothing for a modern server, of course.  It sounds 
like you'd probably run into other scaling issues before you hit memory 
limitations needed to juggle legitimate TCP connection state.
-- 
Brandon Martin