Is the limit_rate per tcp session or per HTTP request?

[Ruslan Ermilov]

On Mon, Dec 21, 2015 at 11:00:09AM +0100, Stefan Hellkvist wrote:
> Hi,
> 
> From reading the code and the docs I have gotten the impression that
> limit_rate (and limit_rate_after) is per ngx_connection which (I think)
> means that it is per HTTP request and not per socket. Am I right in this
> conclusion or is the limit actually per socket/TCP connection?

The docs at http://nginx.org/r/limit_rate says it clearly that the limit
is set per a request, and describes one of the possible cases how this
limit can be "avoided" by the client.

The limit is implemented on the ngx_connection_t level which is usually
mapped 1:1 to a physical connection.

> What we are observing is that the limit we configure does only kick in for
> requests to files that are larger than the limit_rate_after when the
> request is done in one GET request but not when the request is done in
> chunks using byte offset parameters (that is - using many GET requests for
> the file). So clients can easily avoid the limitations by downloading the
> file chunk by chunk rather than in one request.

Opening several connections, or using SPDY/HTTP2 is another way to jump
over the limit.

> If our conclusion are right - that the limit is per HTTP request and not
> per socket so that a chunked download would not be limited - does anyone
> have any suggestion how we would go about to introduce a limit also on
> socket level? I don't mind hacking away at the code, but perhaps someone
> out there has already looked into this?

I know that Valentin (CC:ed) was working on the limit_rate module that
improves things, including variables support and extening the limitation
beyond only "per request".  It should become possible to limit byte rate
per IP, for example.