OT: limit number of connections from browser to my server?

[Grant Edwards]

On 2016-05-16, Chris Angelico <rosuav at gmail.com> wrote:
> On Tue, May 17, 2016 at 2:06 AM, Grant Edwards> <grant.b.edwards at gmail.com> wrote:
>> So, when a browser wants to load a page that has the main html file, a
>> css file, a javascript library or two, and a few icons and background
>> bitmaps, they browser opens up a half-dozen SSL connections in
>> parallel.
>>
>> That's fine when the server is Facebook's server farm.
>>
>> But when it's a small embedded device running at 40MHz with a
>> single-threaded web server and software crypto, it turns a 2-second
>> page load time into a 15-second page load time.

[...]

> If your server is single-threaded, it ought to be processing only one
> connection at a time anyway. Are you sure parallel connections are the
> problem here?

It handles one HTTP request at a time, but it allows multiple
connections to be open simultaneously.  It's got a sort of "event
loop" where each time through the loop it accepts all new connections,
shuts down any closed connections, and then handles requests (one at a
time) on any open connections that are readable.

I can see from the devices logs and from Chrome's network monitor that
it has opened 5-6 parallel SSL connections by the time the page is
loaded.  I can also see that pending HTTP requests on already-opened
connections are being delayed by the SSL connection setup times of the
newer connections.

> The solution might actually be to move all your static files
> elsewhere. Slap 'em up onto github.io or something, and then the
> browser is free to make all the parallel connections it likes; your
> embedded device can just serve the stuff that actually varies
> (presumably the main HTML file). I know that isn't what you asked
> for, but it's something to consider :)

Our devices are often used on air-gapped industrial networks with no
connection to the interwebs.  We can't assume access to any other web
servers.

I've thought about trying to do as much as possible with server-side
includes for .js and .css files and embedding graphics elements in the
HTML pages for icons, background, etc. But, that makes development
more complicated and you give up the advanges of browser caching of
css, js, png, and gif files.

-- 
Grant Edwards               grant.b.edwards        Yow! Is it clean in other
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