Tom Blenko  wrote:
> Another issue. Apache does serve files, e.g., images, but most of the
> non-image content a user sees will come from one of many application
> servers (probably on the other side of an inner-tier firewall from
> Apache). Applications on these servers receive requests forwarded from
> Apache and return responses to those requests for Apache to return to
> the user's browser. Apache serves in a central role but it is largely a
> pass-through for much of the non-image web content.

Indeed, and these days many apps are themselves webservers.  The app's
interface happens to be HTML sent over a TCP socket, and central to the app
is the database that the content is based on (think about Gmail or Google
Docs as an example here).

There can be one or many instances of the app, depending on its complexity,
and the database can be internal or separate.  Traffic to this farm of apps
is directed by frontend server(s), that take care of things like load
balancing, failover and TLS.

Static files like PDFs, images and video are only URL entries in the database -
the URLs are embedded in the output HTML, and the browser fetches them from
a separate server, perhaps a CDN like Akamai, who will redirect that to a
server closest to the user.

At no point is a traditional webserver like Apache involved at all here -
the apps are their own thing written in Python or Node or Java or whatever,
the frontend server is a proxy like HAProxy, and the CDN is a blackbox
service.

It's entirely different from a 1990s Apache install, and that's why all this
discussion about webhosts adding advert headers to content doesn't make
sense.  The content lives in the DB - unless you're writing on a platform
like a blogging service (where the service turns your plain text into pages,
including ads), if you write the app you get to decide what HTML gets
generated and which Javascript callouts you include.  That JS can utterly
change what the user sees, which is why you should be careful what you
include.

Theo

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